We present in this paper the actual status of the LUCIA project, a high average power diode-pumped solid-state laser chain capable to deliver 100 J in nanosecond regime at 10 Hz. In a first step, we deal with the choice of the amplifier medium and the pump and extraction architecture. We present after the thermal management and the cooling architecture. Then, we investigate the damage threshold required. We present last the performances already obtained and the improvements we are working out.

Diode Pumped Solid State Lasers (DPSSL) are gaining increasing interest for high power industrial application, given the continuous improvement in high power diode laser technology reliability and affordability. These sources open new windows in the parameter space for traditional applications such as cutting , welding, marking and engraving for high reflectance metallic materials. Other interesting applications for this kind of sources include high speed thermal printing, precision drilling, selective soldering and thin film etching. In this paper we examine the most important DPSS laser source types for industrial applications and we describe in details the performances of some slab laser configurations investigated at our facilities. The different architectures' advantages and draw-backs are briefly compared in terms of performances, system complexity and ease of scalability to the multi-kW level.

The simultaneous Q-Switching and Mode Locking (QML) regime provides the generation of relatively high peak power picosecond pulses train with energies of a few μJ each in a simple resonator. The critical review of QML methods and results including our investigations is given in the first part of presentation. The application of several types of saturable crystalline absorbers (Cr⁴⁺:YAG, V³⁺:YAG, LiF, GaAs) leads to chaotic, partial QML effect, with less than 100% modulation depth in principle. The fully modulated efficient QML laser was demonstrated in the next part. The acousto-optic cell playing a double role of Q-switch and Mode Locker was located near flat output coupler. The two folding mirrors were mounted on the translation stages for matching the resonance frequency of the cavity to the radio frequency of acousto-optic modulator. The QML pulses with envelope durations of 100-150 ns and 100% modulation depth were observed for wide range of pump powers and repetition rates. In the preliminary experiments up to 3 W of output average power, 100μJ of the envelope energy, having approximately 5-8 mode locked pulses were achieved.

We investigate the performance of a modern hollow-core optical fibre coupled to a GaAs-based quantum cascade laser (QCL) emitting at a wavelength of 10.7 μm. The QCL is operated in pulsed operation with current pulses of 100 ns width at a repetition rate of 10 kHz at a heat sink temperature of 258 K. The emitted light is collected by a f/1.6 ellipsoidal mirror and focused onto the hollow-core optical fibre. The investigated fibre is 2 m long and is designed for a transmission wavelength of 10.6 μm. After the transmission through fibre, the light is collected by a ZnSe-aspheric lens. We investigate the transmission efficiency of the hollow-core optical fibre and its influence on the intensity noise properties by measuring the transmitted optical peak power in relation to the emitted optical peak power. We find a total transmission loss of 6.25 dB. We then analyze the influence of this hollow-core optical fibre on the intensity noise properties of the QCL in terms of the relative intensity noise (RIN). We find that for the same detected optical peak powers the RIN of the optical power transmitted through the fibre is about 4 dB/Hz lower than the RIN of the emitted optical power. We attribute this reduction of the RIN level to a random selection process of photons due to the losses of the fibre which alters the intensity noise towards the standard quantum limit.

Thin disc lasers represent a new class of welding lasers in that they combine the beneficial characteristics of CO₂- and Nd:YAG-lasers. Their good focusability--values of M² around 20 are typical for devices in the multi kW power range--can be utilized in several ways to improve the welding performance: compared to lamp-pumped Nd:YAG-lasers, the laser power required at the threshold to the deep penetration regime can be reduced, the welding depth can be increased and far higher values of traverse speed are applicable at prescribed welding depths. Alternatively, the high beam quality allows the use of focusing optics with large focal lengths, hence enabling the realization of "remote welding" concepts. At the same time, a wavelength of 1.03 μm (Yb:YAG) provides, in comparison to CO₂-lasers, a high absorptivity at metallic workpieces and a low sensitivity against plasma production; both effects contribute to the efficiency, stability and achievable quality of the welding process. Further, beam delivery via flexible glass fibers with core diameters of 100 μm to 150 μm is possible. With these features and an overall (plug) efficiency of more than 20 %, this laser offers a large potential for many applications.

The paper presents a part of the results of EUREKA E!2542 RENOVA LASER project "Laser renovation of monuments and works of art", realized in the years 2001-2004, aimed to the application of laser technique to the conservation of artworks and historic objects in architectural scale. Laser technology has been blended into the full program of conservation and restoration of Sigismund's Chapel at Wawel Castle in Cracow, Poland, including more than 800 m² of decorative, XVI century sculptor's surfaces.

We have developed the photonic sensor of electromagnetic field. The electrooptical phase modulator inserted in one laser cavity performs frequency modulation of the laser due to voltage induced in the antenna probe. The heterodyne detection allows to move the spectrum of modulated optical frequencies into the RF or microwave ranges. The issue of our solution is inserting of both lasers (signal and reference) in the common construction in order to minimize fluctuation of offset frequency. The pumping of the microchip lasers and transmission of the signal are guided via optical fibers. The setup can be all dielectric (apart of antenna). The sensitivity of laser tuning with an electrooptical modulator i.e. the value of frequency deviation due to driven voltage is linearly proportional to the free spectral range of the laser and inversely proportional to the "half-wavelength" voltage of an used modulator. In our case this sensitivity is about 10 MHz/V, with the free spectral range ν_q congruent to 28 GHz. The sensitivity is quite high, even when the offset frequency fluctuation, caused mainly by thermal drift, are taken in account. Apart from the heterodyne technique of optical FM detection we have introduce here detection with the external Fabry-Perot cavity

Electron paramagnetic resonance (EPR) measurements of LiNbO₃: Yb, Pr (0.8wt.%, 0.1 wt.%) single crystals were analyzed for lattice sites of Yb in the crystal and also for the Yb³⁺ pairs arising. Parameters of the spin Hamiltonian were calculated using EPRNMR program. From the angular variations of the EPR spectra it results Yb³⁺ ions of C₁ symmetry arise in the crystal. Pr³⁺ ions change parameters of spin hamiltonian for Yb³⁺ ion. Some results of the absorption measurements were also analyzed for UV-VIS and IR giving evidence, together with EPR results, on Yb³⁺ location at Li⁺ sites and Pr³⁺ location at Nb⁵⁺ sites. For comparison absorption spectra of the LiNbO₃ doped with 0.5 wt. % Pr³⁺, 0.8 wt. % Yb³⁺ were analyzed. Low temperature absorption measurements have shown the presence of low energy phonons responsible for the intensity of the main Yb³⁺ absorption line in IR as a function of the temperature. Raman spectra confirmed the observation.

A colliding enhance resonator (CER) was used in a passively Q-switched Nd:YAG laser. Cr⁴⁺:YAG crystal and color centered LiF:F₂^- crystal were selected as Q-switched elements. A high energy and high stability single Q-switched pulse was obtained. Energy stability is as high as 99% which is comparable to an actively Q-switched laser. Output energy has increased 40~60% compared to a conventional resonator (CR) Q-switched laser at the same condition. Numerical calculation has shown the excellent agreement with experimental result.

Designing strategy to enhance mode selectivity of higher-output vertical-cavity surface-emitting diode lasers (VCSELs) is presented using the oxide-confined GaAs-based (GaIn)(NAs)/GaAs quantum-well VCSEL with two oxide apertures on both sides of its central active region as a typical example. A general strategy is to shift one aperture to the node position of the resonator standing wave where it is working as the electrical aperture only. Then diameters of both the apertures may be changed independently giving an additional degree of freedom for VCSEL designing. The comprehensive optical-electrical-thermal-gain self-consistent approach is used to simulate anticipated performance characteristics of the modified VCSEL. The single fundamental mode operation has been predicted in a large-size device with the 10-μm-diameter active region even for 80 K active-region temperature increase over the room ambient temperature. A similar radial waveguiding may be also produced in VCSELs with the aid of photonic crystals which have been found to create a very efficient discrimination mechanism for higher-order transverse modes. Therefore photonic-crystal confined VCSELs seem to be very promising structures in their future applications.

We present preliminary results on low-threshold compact edge-emitting laser structures incorporating high-reflectivity 1D photonic crystal mirrors. In addition we present 2-D FDTD simulation results of the mirror reflectivity and application of selective oxidation for the purpose of current confinement, hence reduction of threshold current. 84um cavity length 1D PC lasers are demonstrated to have a threshold current of approximately 5mA, reduced to 1.7mA upon application of oxide confined current aperture.

The coupling phenomena dependence with the lateral separation between the laser stripes in laterally coupled diode lasers is of major importance for the design of these devices as a solution to overcome the intrinsic bandwidth limitation of semiconductor lasers. In this work an experimental study of the coupling dependence with the separation between laser stripes is presented. For that purpose a comparison of the spectrally resolved near and far fields and of the frequency responses obtained with the laterally coupled diode lasers for devices with different separation between the ridges is made.

In the paper a new concept of digital holographic tomograph (DHT) based on interferometric tomography and digital off-line holography is presented. Capability of registration of microobjects located at different distances from hologram is the basic characteristics of DHT. This feature is used in order to register an object in several views. This is performed by a multiple pass arrangements. However such multipass configuration brings a lot of new issues to be considered including the proper identification of information from sequential pass through object, analysis of the influence of diffraction and others on the object reconstruction. Therefore the extended simulations of reconstruction of amplitude and phase microobjects by means of digital holographic interferometry are performed. The pros and cons for using multipass DHI as the source of data for tomographic reconstruction of amplitude-phase microelements are discussed.

Two-beam interferometry enables information coding in the shape/orientation and contrast/intensity modulation of the fringes. There exists an abundant literature on decoding the interferogram phase whereas there are only a few studies dealing with the second type carrier decoding. This paper is focused on the two-beam interferogram intensity modulation analysis using temporal phase shifting. The influences of most important experimental errors are studied using computer simulations and laboratory works. Null and finite-fringe detection modes are compared. Phase-shift histograms and their lattice-site representations are investigated to aid the experimental error identification.

The study of digital holographic system with partially spatially coherent illumination is presented. The analysis concerns digital lensless Fresnel holography with stationary object illumination. We propose a criterion for selection of optimal partially coherent beam to get maximum noise reduction while maintaining full system resolution. The theoretical results are applied to 3D simulation and a laboratory experiment.

Micro-Electro-Mechanical Systems are nowadays frequently used in many fields of industry. The number of their applications increase and their functions became more complex and demanding. Therefore precise knowledge about their static (shape, deformations, stresses) and dynamic (resonance frequencies, amplitude and phase of vibration) properties is necessary. Two beam laser interferometry is one of the most popular testing methods of micromechanical elements as a non-contact, high-accurate method allowing full-field measurement. First part of the paper present microbeam actuators designed for MEMS/MOEMS applications. The proposed structures are the straight silicon microbeams formed by KOH etching of Si wafer. Aluminium nitride (AlN) thin films are promising materials for many acoustic and optic applications in MEMS field. In the proposed architecture the actuation layer is sandwiched between two metal electrodes on the top of beam. In the second part we describe the methodology of the actuator characterization. These methods applied are: stroboscopic interferometry and active interferometry (LCOS SLM is used as a reference surface in Twyman-Green interferometer). Moreover some results of FEM analysis of the sample are shown and compared with experimental results. Dynamic measurements validate the design and simulations, and provide information for optimization of the actuator manufacturing process.

We present an optical conveyor belt that provides trapping and subsequent precise delivery of several sub-micron particles over a distance of tens of micrometers. This tool is based on a standing wave (SW) created from two counter-propagating evanescent beams where the phase of one of the beams can be changed. Therefore, the whole structure of SW nodes and antinodes moves and deliver confined microobjects to specific regions. Based on the theoretical calculations we confirm experimentally that certain sizes of polymer particles can be more easily delivered but other sizes do not feel the SW motion at all.

Recent growth of micro and nano technology offers large variety of micro scale devices, which gradually replace bulk appliances of everyday use. MEMS devices are being used in medical, science research, military and industrial applications. Since their technology is not fully mastered yet, they require special measurement treatment from stage of production to stage of utilization. Most of nowadays used bulk measurement instrumentation require special preparation of MEMS element to test (putting elements on special stages or combining MEMS devices with cheap and simple instrumentation (fiber sensors)). Since MEMS technology is meant to be inexpensive a trend of building MEMS measurement instrumentation for nano and micro elements testing appeared. In this paper we present the concept of novel multifunctional waveguide interferometer for three components of displacement vector measurement of elements with optical or rough surfaces. The measurement system combines the various techniques: conventional Twyman-Green (TGI), grating (moire) interferometry (GI), ESPI and digital holographic interferometry (DHI). It consists of several modules such as light source and detector integrated module, passive interferometric module, waveguide interferometer head and MEMS based active beam manipulators. The proposed design of modules decrease significantly their sensitivity to vibration, so that they can work in instable environment.

This article presents the usage of coupled dipole method for calculation of optical binding between two dielectric spheres placed in two counter-propagating Gaussian laser beams that do not interfere. The results show that there exist combinations of the refractive indices of the particle and the surrounding medium where two stable distances between spheres exist.

An efficient double-clad erbium-ytterbium co-doped fiber laser pumped by two high-power diode-stacks at 975nm is reported. Using a simple external cavity configuration at one end of the fiber and the 3.6% Fresnel reflection from a cleaved fiber end facet at the opposite end of the fiber to provide the necessary feedback for lasing, we obtained a maximum output power of 159W at 1565nm in a beam with beam quality factor (M²) ~1.9 for 466W of launched pump power. The corresponding slope efficiency with respect to launched pump power was 34%. The maximum output power was limited by the available pump power. A strategy for increasing the output power and improving the beam quality based on the use of a double-clad fiber design with a helical-core trajectory is considered.

Up-conversion fiber lasers based on Pr³⁺/Yb³⁺ doped fluoride fibers and pumped at 835 nm can operate on emission lines in the red, orange, green, and blue spectral region. Up to now only Fabry-Perot configurations with two mirrors butt-coupled to the fiber ends were investigated. In this paper we present the first visible Pr³⁺/Yb³⁺ fiber lasers in a ring configuration. In contrast to the usual Fabry-Perot configuration, the basic ring resonator setup contains no free-space optics and no parts which need to be adjusted. The main challenge for such a setup is the connection between the fluoride laser fiber and the remaining part of the ring resonator, which is made from silica fibers. Due to the very different melting temperatures of both glasses usual fusion splices are impossible. We use a special technique to couple the fibers with glue.

We demonstrate laser emission in polymer-based microrings doped with a near infrared emitting dye, 2-(6-(4-Dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-methyl-benzothiazolium perchlorat. We fabricate our poly(1-vinyl-2-pyrrolidone)-based microrings containing 0.5 wt % of the dye. They exhibit lasing at around 840 nm under transverse nanosecond photoexcitation at 532 nm. Optical feedback is provided by total internal reflection. The threshold for lasing is found to be 311 μJ/cm². The cavity has a Q-factor larger than 2000, which is limited by the resolution of our detection system.

We present an erbium-doped fiber laser mode-locked using a reverse-biased InGaAsP multiple quantum-well saturable absorber. We have examined the performance of a p-type-intrinsic-n-type (PIN) structured semiconductor absorber mirror both in starting the pulse operation and in pulse shaping. We have also found that applying a reverse bias is a useful means to suppress the Q-switching instability. By varying the reverse bias voltage applied to the absorber mirror, we could change the recovery time of the device owing to the electric-field-induced carrier sweep-out. Through the sweep-out process we were able to control the mode-locking start-up capability and the pulse duration of the fiber laser. In the experiment the mode-locked pulse duration could be reduced from 50 to 20 ps by application of an 80 kV/cm sweep-out field in the intrinsic region of the PIN absorber. The equivalent spectral broadening by a factor of 2.5 was observed as well.

There is a necessity of development a stable and calibrated laser sources for modern WDM telecommunication systems. Additionally simultaneous oscillations of many wavelength are required for testing and diagnostic of such systems. This regime of operation is possible in Frequency Shifted Feedback Lasers (FSFL). The multiwavelength erbium doped fiber laser is presented in this paper. The acoustooptical Bragg frequency shifter (AOFS) in the laser cavity ensures stable and multi-frequency operation by preventing steady-state regime. The wavelengths forced by Fabry-Perot filter cover part of third window (1550 nm).

In this work we present a new mode-locked device that can be used for millimeter-wave photonic applications. Such device presents for certain bias conditions a dual-mode behavior we have investigated for millimeter wave generation. Through the small signal analysis of the device, we have identified a resonance at the frequency separation of the longitudinal modes that has allowed us to demonstrate signal transmission at 40 GHz. The millimeter wave signal generated in detection is studied in terms of phase noise and the noise intrinsic to the emitter.

Broad area lasers can provide an optical beam with high power, but at the expense of low beam quality. One of the ways to improve their brightness is to operate broad area lasers in an external cavity scheme, using free-space optics to provide spatial and spectral filtering. Bent waveguide lasers have been proposed to eliminate undesirable resonances caused by the antireflection coated facet of the laser, which would impair the proper operation of the external cavity. In this paper, the influence of the bend radius, waveguide width and refractive index contrast on the properties of the bent waveguide cavities has been investigated. For the purpose of the analysis, the wide-angle finite difference beam propagation method was used.

We demonstrate the applicability of imaging thermography for investigations of mechanisms associated with gradual degradation in diode lasers. The introduction of two spectral channels provides the means for separate observation of deep level luminescence and thermal radiation emitted according to Planck's law. In the near IR region we found the signal detected by the camera to be mainly affected by mid-gap deep-level luminescence. An intensity increase of the luminescence signal for an aged diode laser compared to an unaged device is noticed. It can be explained by an increase of deep level defect concentration during the aging. In the mid IR, we mainly encounter thermal radiation, which can be used for the analysis of the thermal properties of devices. In present work the thermal behavior of the device subjected to an aging of 3000 hours is analyzed. A significant increase of device temperature is noticed.

A uniform Bragg grating as dispersive device of InGaAsP/InP integrated chirped pulse compressors are studied. Results of numerical analysis for the propagation of chirped ultrafast pulses are presented. The compression factor and the length of the device have been designed looking for an optimum behaviour for a monolithic implementation in a 40 GHz mode-locked diode laser.

Up until recently the successful growth of nitride optoelectronic devices had been demonstrated only with Metal Organic Vapor Phase Epitaxy (MOVPE) due to the possibility of growth of GaN at temperatures which exceed 1000C. Molecular Beam Epitaxy (MBE) seemed to be less adapted for this purpose. It was believed that MBE can give good results only if the growth conditions are close to these used in MOVPE reacotors. Indeed, the first successful growth of laser diode (LDs) was obtained using ammonia MBE at temperatures as high as 950^oC. The new perspective has been opened recently by successful growth of LD structures on nearly dislocation free GaN bulk substrates using Plasma Assisted MBE at much lower temperatures of 590-710^oC. The laser structures are deposited on the high-pressure-grown low dislocation bulk GaN substrates taking full advantage of the so called adlayer enhanced lateral diffusion channel for adatoms below the dynamic metallic cover. Devices grown by PAMBE on bulk substrates compare very favorably to the early laser diodes fabricated using the MOVPE technique, providing evidence that the relatively low growth temperatures used in this process pose no intrinsic limitations on the quality of the optoelectronic components. This opened up a number of new possibilities to the low temperature PAMBE including high power blue LDs, green and UV LDs, and quantum cascade lasers.

An integrable device for pulse compression based in a directional coupler is presented. InGaAsP/ InP materials have been used in order to design an integrable structure. The length of the device is calculated in vertical and lateral guides. Each of the supermodes in the total structure presents a giant Group Velocity Dispersion (GVD) which make possible to obtain total pulse chirp compensation if the pulse propagates enought distance into the guides. In case of vertical structures, two guides of InGaAsp have been used to obtain GVD's of 10⁵ ps²/Km wich allow high compression rates. Secondly we have designed a directional coupler using lateral coupled guides calculated with Efective Index Method (EIM) and values arround 4 10⁴ ps²/Km have been achieved. Both designs are compared between then taking into account several important parameters as device length and fabrication issues.

The present trends in the development work on X-ray lasers are shown and discussed on a background of a brief history of the collisionally pumped X-ray lasers. The presentation is focused on two variants of the transient inversion pump method succesfully applied in the experiments - slab target geometry and single profiled laser pulse. Recently, another scheme referred to as GRIP (GRazing Incidence Pumping) has been proposed and demonstrated. This pump geometry opens the new real possibility to construct a repetitive X-ray laser. Some aspects of the pump scheme implementation are discussed in detail. Finally, a specific injector-amplifier system giving a new perspective on the future of X-ray lasers is dicussed briefly as well.

The XeCl excimer laser Hercules at ENEA Frascati, thanks to its peculiar features, is a unique laser-facility for many irradiation experiments. Among these applications, most machine-time is devoted to drive a laser-plasma source. This laser-plasma source is used for high-resolution atomic spectroscopy, in vivo contact microscopy of biological samples, induced DNA damage, micro-radiography, generation of sub-micron luminescent pattern on Lithium Fluoride films for miniaturized active optical devices. Recently, we equipped the Hercules-driven laser plasma source with a novel Debris Mitigation System to drastically reduce the amount of hot debris emitted by the solid target (potentially dangerous for optics, filters and detectors put near the plasma). Here we will discuss the challenging attempt of stopping debris emitted by our solid-target laser plasma, in order to achieve a clean and efficient EUV source.

Organic polymers (PMMA, PTFE, PET, and PI) are considered as the important materials in microengineering, especially for biological and medical applications. Micromachining of such materials is possible with the use of different techniques that involve electromagnetic radiation or charged particle beams. Another possibility of high aspect ratio micromachining of PTFE is direct photo-etching using synchrotron radiation. X-ray and ultraviolet radiation from other sources, for micromachining of materials by direct photo-etching can be also applied. In this paper we present the results of investigation of a wide band soft X-ray source and its application for direct photo-etching of organic polymers. X-ray radiation in the wavelength range from about 3 nm to 20 nm was produced as a result of irradiation of a double-stream gas puff target with laser pulses of energy 0.8 J and time duration of about 3 ns. The spectra, plasma size and absolute energies of soft X-ray pulses for different gas puff targets were measured. Photo-etching process of polymers irradiated with the use of the soft X-ray radiation was analyzed and investigated. Samples of organic polymers were placed inside a vacuum chamber of the x-ray source, close to the gas puff target at the distance of about 2 cm from plasmas created by focused laser pulses. A fine metal grid placed in front of the samples was used as a mask to form structures by x-ray ablation. The results of photo-etching process for several minutes exposition with l0Hz repetition rate were presented. High ablation efficiency was obtained with the use of the gas puff target containing xenon surrounded by helium.

Advantageous features of Chemical Oxygen-Iodine Laser (COIL) for laser technologies have increased considerably activities of international COIL communities during past ten years. They have been focused on the advanced concepts of hardware designs of the COIL subsystems, and testing and scaling-up of existing laser facilities. Prospective special applications of COIL technology, both civil and military, have received a significant attention and gained concrete aims. The paper is introduced by a brief description of the COIL operation mechanism and key device subsystems. It deals then with presentation of some investigated advanced concepts of singlet oxygen generators, alternative methods for atomic iodine generation, a mixing and ejector nozzle design to downsize a pressure recovery system, and optical resonators for high power COIL systems. The advanced diagnostics and computational modeling are also mentioned as very useful tools for critical insight into the laser kinetics and fluid dynamics, supporting thus the COIL research. The recent progress in the COIL development moves this laser closer to the application projects that are also briefly presented.

The laser with power tens of kilowatt would be essential for dismantlement of obsolete nuclear-power reactors, laser-hardening the surfaces of railway rails and etc. The production of high power, high efficiency, high specific energy and high optical beam quality can be obtained in the experimental systems of a quasi-cw electroionization CO laser with cooling a CO mixture by its expansion in the nozzles. The way of transfer to industrial high-power CO lasers is proposed through the continuous formation of a CO laser mixture during laser operation. CO laser mixture is formed by using air as a buffer gas (about 90%). CO molecules are generated in oxidation reaction of oxygen-containing molecules with carbon. The carbon arises from a decomposition of hydrocarbon fuel on the catalyst surface. CO mixture is excited by radio-frequency (RF) electric discharge in a supersonic gas flow without an electron gun. The given conception was used on a small-scale model system to demonstrate that the laser radiation was possible in a CO mixture with combustion products and air, which are excited by RF discharge in a supersonic flow. The industrial CO laser with tens of kilowatt power is offer with open working cycle without ejecting toxic CO into the atmosphere by converting CO molecules to C0₂ ones. The estimated cost of a laser is several hundred thousand and the small sizes of laser give possibility to install its on manipulator without fiber-optic delivery.

The influence of the buffer gases on the discharge homogeneity of F₂doped excimer laser gas mixtures is investigated in a small x-ray preionised high-pressure discharge chamber. The spatial and temporal development of discharges in He/F₂ and Ne/F₂ gas mixtures is monitored via its fluorescence using an intensified CCD camera with a gating time of 300 ps. The formation and development of discharge filaments in He/F₂ gas mixtures is completely different from that in Ne/F₂. Under the same start up conditions, discharges in Ne/F₂ are dominated by cathode hotspots where as no hot spots are visible in discharges in He/F₂ gas mixtures. However, the discharges in Ne/F₂ gas mixtures appear to be more uniform even though the discharge width decreases in time and hotspots are persistent on the cathode surface.

A technique for obtaining a pulse-periodic operating mode of high-power wide-aperture lasers (GDL, HF/DF, COIL) was put forward theoretically and experimentally realized for the case of GDL. The possibility of realizing a pulse-periodic mode in high-power wide-aperture lasers without a sacrifice in average output power was experimentally demonstrated and applicability of the realized approach for lightcraft technology further development is pointed out. Regime of light supported detonation wave and effect of shock waves joining for this particular application were investigated.

In this work, after construction of a copper chloride laser, the effect of using different buffer gases on the output power has been examined. The voltage, current, laser pulses and the far field pattern of laser intensity were measured at the optimum buffer gas pressure. At these favorable conditions, the effect of using diaphragms in different diameters on the specific output power has been studied. By finding the desirable diaphragm size which creates the best temperature gradient in the laser tube the specific output record power of 123 (Watt/Lit) was obtained.

An advanced nozzle, also known as ejector nozzle, suitable for a 500 W class COIL employing an active medium flow of nearly 12 gm/s has been developed and used instead of conventional slit nozzle. The nozzle has been tested in both cold as well as hot run conditions of COIL achieving a typical cavity pressure of nearly 10 torr, pitot pressure of ~ 85 torr and a cavity Mach number of ~2.5. The present study details the gas dynamic aspects and detailed numerical studies of this ejector nozzle and highlights its potential as a COIL pressure recovery device. This nozzle in conjunction with a diffuser is capable of achieving pressure recovery of ~ 60 torr, equivalent to the much cumbersome first stage of the pressure recovery system used in case of conventional slit nozzle based system. . Thus use of this nozzle in place of conventional slit nozzle can achieve the atmospheric discharge using single stage ejector system thereby making the pressure recovery system quite compact.

Merging modes of optical pulsed discharge generating shock waves conditions are determined for the different parameters of gas pressure, energy and repetition rate of laser pulses. Quasi-stationary wave formation characteristics due to moving as well as stationary optical pulsating discharge for the cases of single reflector and matrix of reflectors will be discussed. Advantages of quasi-stationary wave mode for Lightcraft engine applications will be demonstrated.

Results of the investigations on an RF pulsed excited CO₂ laser plasma are given in the paper. A slab-waveguide configuration of the laser is used. An unstable positive branch resonator structure is applied to ensure a single-mode operation of the laser. The configuration of the laser system guaranties a spectral purity of the laser output radiation, and makes the investigations clear. As known, a pulse excitation introduces dramatic perturbations of the laser plasma pressure, and temperature. The density of the laser gas mixture, or in other words, the refractive index is changed during the input pulse developing, as a consequence. The laser radiation frequency is changed in time of the laser pulse duration. Sometimes it is a parasitic effect, when a single-frequency laser operation is required. The aim of the work is to give a clear picture of the laser plasma behavior caused by a pulse excitation of the laser medium. The results obtained gives a possibility to elaborate the method of a laser frequency control in a pulsed regime.

A review on the results achieved by our group in the development of novel solid-state lasers for Lidar applications at 2 μm is presented. These lasers, based on fluoride crystals (YLF₄, BaY₂F₈, and KYF₄) doped with Tm and Ho ions, are characterized by high-efficiency and wide wavelength tunability around 2 μm. Single crystals of LiYF₄, BaY₂F₈, and KYF₄ codoped with the same Tm³⁺ and Ho³⁺ concentrations were successfully grown by the Czochralski method. The full spectroscopic characterization of the different laser crystals and the comparison between the laser performance are presented. Continuous wave operation was efficiently demonstrated by means of a CW diode-pumping. These oscillators find interesting applications in the field of remote sensing (Lidar and Dial systems) as well as in high-resolution molecular spectroscopy, frequency metrology, and biomedical applications.

Sensitive heterodyne detection with lasers applied .to radar and satellite communication is seriously hampered by the large electronic bandwidth due to random Doppler shift and frequency instability. These drawbacks can be circumvented by dual signal heterodyne detection. The system consists of mixing the local oscillator with two signal beams and the lock-in amplification at the beat frequency of the two intermediate frequencies. The signal modulation is demodulated by the lock-in amplification. A detailed analysis of the accompanying noise is given. The derived NEP is much smaller than that of a conventional heterodyne system. As examples, the system is applied to radar and space communication.

The threat of hostile surveillance and weapon systems require military aircraft to fly under extreme conditions such as low altitude, high speed, poor visibility and incomplete terrain information. The probability of collision with natural and man-made obstacles during such contour missions is high if detection capability is restricted to conventional vision aids. Forward-looking scanning laser radars which are build by the EADS company and presently being flight tested and evaluated at German proving grounds, provide a possible solution, having a large field of view, high angular and range resolution, a high pulse repetition rate, and sufficient pulse energy to register returns from objects at distances of military relevance with a high hit-and-detect probability. The development of advanced 3d-scene analysis algorithms had increased the recognition probability and reduced the false alarm rate by using more readily recognizable objects such as terrain, poles, pylons, trees, etc. to generate a parametric description of the terrain surface as well as the class, position, orientation, size and shape of all objects in the scene. The sensor system and the implemented algorithms can be used for other applications such as terrain following, autonomous obstacle avoidance, and automatic target recognition. This paper describes different 3D-imaging ladar sensors with unique system architecture but different components matched for different military application. Emphasis is laid on an obstacle warning system with a high probability of detection of thin wires, the real time processing of the measured range image data, obstacle classification und visualization.

We describe a new development of differential absorption DIAL spectrometric system based on the mid-infrared tunable Optical Parametric Oscillator (OPO), pumped by compact Q-switched lasers. Mobile LIDAR was assembled in the truck and is devoted for selective pollutant analysis in the distance range extending from hundred of meters to a few kilometers. A reliable cascade mid-IR generation scheme was developed. Pulse energies up to milijoule in mid-IR (λ=8-12 μm) have been already obtained using nonlinear AgGaSe₂ crystal. The collinear optical scheme with 25cm (10inch) gold mirror telescope, MCT thermoelectrically cooled detector with control electronics was tested at 250m optical length and currently is under further development.

We analyze two different physical mechanisms that can stabilize optical vortices in self-focusing nonlinear media which are known to be unstable due to the azimuthal modulational instability. First, we show that vortices become stable in self-focusing nonlinear media with nonlocal nonlinearity. Second, we study optical vortices created by self-trapping of partially incoherent light with a phase dislocation and show that such partially incoherent optical vortices are stabilized when the spatial incoherence of light exceeds a certain threshold value.

We show theoretically how charge distribution in low-dimensional semiconductor heterostructures is manipulated and controlled by means of linearly polarized, strongly asymmetric electromagnetic pulses. In particular we point out the possibility of generating a charge polarization and charge currents in mesoscopic rings and how these non-equilibrium phenomena can be utilized as a source for electromagnetic radiation and for the generation of magnetic states in the rings. Possible relaxation and decoherence pathways are investigated by means of the density matrix formalism and typical time scales for the survival of the generated non-equilibrium charge distributions are estimated.

Twisted light, or light with orbital angular momentum (OAM), plays an emerging role in both classical and quantum science, with important applications in areas as diverse as biophotonics, micromachines, spintronics, or quantum information. It offers fascinating opportunities for exploring new fundamental ideas in physics, as well as for being used as a tool for practical applications. One important point is to determine how to generate single photons, and two-photon states, with an appropriate OAM content. Here we describe the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric down-conversion (SPDC) in different non-collinear geometries. These geometries introduce a variety of new features. In particular, we find the OAM of entangled pairs generated in purely transverse-emitting configurations, where the entangled photons counter-propagate perpendicularly to the direction of propagation of the pump beam. The spatial walk-off of all interacting waves in the parametric process also determines the OAM content of the down-converted photons, and here its influence is also revealed.

The optical vortex interferometer (OVI) is new optical instrument based on the regular net of optical vortices. Such net is generated by interference of three plane waves. In this paper the phase shifting method named internal scanning method, which enhances the OVI possibilities is discussed. The possible applications of this new method are also presented in brief.

Method of direct oscillation at radially or azimuthally polarized transverse modes in an optical resonator is presented. The optical resonator consists of a w-axicon, a polarization controlling feedback axicon mirror, and a flat output coupler. The central axicon of the w-axicon is made to slide forward and backward relative to the outer axicon, that leads to the selection of the arbitrary order of the LG₀^±l Laguerre-Gaussian modes. By selectively suppressing the p-polarization or s-polarization of the axicon reflector, the oscillation modes are forced to the radially or azimuthally polarized. A preliminary experiment proves such a resonator is viable and numerical simulation predicts the oscillation characteristics of the proposed resonator.

Two kinds of experiments were performed to observe the ablation characteristics with a pulsed intense UV laser beam. The former was ArF laser ablation experiment to gather data, which were useful for the near future design of the nuclear fusion reactor chambers. The latter was the same laser ablation experiment to get various materials, which were useful in the material sciences including the bio and industrial engineering. Our interests for the uses of this laser beam arise from the modeling of the similar ablation processes for the future applications.

The article describes the modification of fluoropolymers by UV-irradiation with wavelengths below 200 nm in a reactive or inert atmosphere. Light sources employed are excimer lamps, excimer-lasers or F₂-lasers. Special emphasis is put on adhesion phenomena of fluids, biological cells and metal coatings at the modified surfaces.

Worldwide manufacturers have already recognized the advantages of using laser welding for a number of applications. Although laser welding is usually performed autogenously, the use of wire filler allows a broader range of welding applications. In this paper a finite element model for key-hole laser welding sources based on experimental observations is presented. The shape for the heat source can be easily changed so to simulate both autogeneous and wire filler laser welding. In the thermal and mechanical calculations the material properties were considered with full temperature dependence. Austenitic stainless and aluminum alloy welds were chosen to validate the model. Simulations of out-of-plane welds were computed using a local coordinates system. A personal computer was used for the calculations. For different plate thicknesses and weld geometries, the calculated fused zones were found in very good agreement with the experimental ones, which proved that the thermal history was computed correctly. When materials with thermal induced microstructure changes are welded, the microstructure in every point of the heat affected zones can be determined as a function of the local temperature cycle.

Applying of laser technologies offer many new possibilities for achieving conducting materials with modified properties. Laser processes also allow microfabrication of elements of dimension in micrometer scale. The modified materials and elements were obtained by special using of such a laser technologies as rapid remelting, microalloying, removing of material. For some cases, the required energetic parameters of the laser beam have been established and especially developed technological ideas have been presented. Microstructure evolution and phase identification of treated materials was investigated by means of optical and scanning microscopy and X-ray microanalysis. It has been shown that in these technological processes it was possible to achieve conducting materials with changed properties, among other things with modified electrical resistivity. In selected cases it was also possible 3_D shaping of modified elements. The results of investigations were applied for laser welding of joints in power devices, laser microsoldering of IC on PC-board, producing some contact materials.

Ultrafast structural changes in the subpicosecond time domain were studied by using X-rays produced by a femtosecond laser. An upgraded 1 kHz table-top laser was used for optical pump X-ray probe experiments on germanium crystals. The number of laser generated Ti Kα and Cu Kα photons are either 5×10¹⁰ or 1.2×10¹⁰ per second. In this study, the Ti Kα rays were Bragg reflected on the 311 net planes of a toroidal silicon crystal. The germanium sample crystal was placed in the focus of the Ti Kα radiation and reflected it from the 111 plane to be detected by a CCD camera. An ultrafast optical pulse caused by the same kHz laser generates reversible strain pulses in the germanium crystal. By using different time delays between pump and probe pulses time-resolved rocking curves were obtained. The thermoelastic model of Thomsen, used in rocking curve simulations satisfactorily, explains the main features of strain evolution in Ge. Explanation of the remaining deviations between experimental and simulated curves needs a consideration of band gap deformation potential to be included in the simulation.

The efficient cw Mode Locking (cw-ML) regime was demonstrated in Nd:YVO₄ laser by means of saturable absorber mirror (SAM). The 0.3-at.% Nd³⁺ doped 10-mm-long YVO₄ crystal end pumped by 20 W diode module with beam shaper was applied as a gain medium located in the close vicinity to the rear flat mirror of first arm of Z-type resonator of 316 cm total length with two curved mirrors of 100-cm curvature radii. The SAM of 2%-saturable absorptance and saturation fluence of 0.050 μJ/cm² was mounted at the opposite end of resonator. The developed "dynamically stable" cavity design mitigates detrimental role of thermal aberration in gain medium, enforcing clean perfect mode locking even for highest pump densities. The cw-ML pulses with 47.5 MHz repetition rate and pulse durations in the range of 15-30 ps were observed for wide range of pump powers and output coupler losses. In the best case for 32% of output coupler transmission, up to 6.2 W of average power with near 35% slope efficiency were achieved. The thresholds for Q-switched ML, cw-ML regimes were 2.67 W and 6.13 W of pump power, respectively. For the maximum pump power of 20 W we obtained 133 nJ of pulse energy with 16-ps pulse duration, resulting in peak power higher than 8 kW. The threshold energy density at SAM giving the QML regime was estimated to be about 0.030 μJ/cm², threshold of cw-ML regime was 0.220 μJ/cm².

Review of thermo-optic effects in gain media of diode end pumped lasers is presented. Degradation in beam quality due to these effects is analyzed theoretically and verified in experiments. The slit scan method was implemented for registration of intensity profiles along the caustics of laser beam. The M² parameter, coherence degree, and thermal lens power of gain medium in dependence on pumping rate, were determined using Wigner transform and ABCD methods. Investigations of neodymium lasers (Nd:YVO₄, Nd:YAP) operating in free running or Q-switching regimes were carried out. Detrimental role of up-conversion processes for Nd:YAP laser was shown.

The efficient, eye-safe, high repetition rate, intracavity optical parametric oscillator (IOPO) inside acousto-optic Q-switched Nd:YVO₄ laser end pumped by 15-W fiber coupled diode was demonstrated. The pumping Q-switched laser gives 3-W average output power at 1064-nm wavelength and 40-kHz repetition rate. The additional separating mirror, 'x-cut' KTP crystal and the output coupler, highly reflective at 1064-nm and partially transparent at 1572-nm wavelength, form flat-flat IOPO resonator of 35-mm length. We have achieved 3-ns duration pulses for 20-mm long KTP and 4-ns duration pulses for 30-mm KTP length, respectively. Above 10-kW peak power pulses with the average power of 1.5 W at the signal wavelength for 40 kHz repetition rate were demonstrated. Due to intracavity gain guiding effect, diffraction limited signal beam was achieved. Conversion efficiency of 50% with respect to Q-switched output at 1064-nm wavelength and 11% with respect to diode pump power were achieved.

The main features of passively Q-switched microchip lasers development are considered. The active medium of laser is an epitaxial structure combining an epitaxial layer of saturable absorber Cr⁴+:Y₃Al₅O₁₂ (Cr:YAG) grown on substrate of generating crystal Nd:YAG by liquid phase epitaxy. The modulator layer has an initial optical absorption of 36 cm^-1 at wavelength of lasing (1064 nm). The epitaxial layer grown on unworking side was mechanically removed and this substrate side was optically polished. The other one was processed precisely to needed thickness. The cavity's mirrors were deposited by electron beam technique directly on each side of the structure to form a rugged, monolithic resonator. Diode laser Model ATC-C4000 with lasing wavelength 808 nm provided the CW end pumping. The output pulses parameters were investigated by means of test bench consisting of photoelectric transducer FEK-15 and Digital Phosphor Oscilloscope TDS 5052B. The obtained laser parameter are as follows: pulse width (FWHM) about 1.3 ns, repetition rate 5.5 kHz, average output power about 10 mW, pulse energy 1.0 μJ, pick power 1.2 kW. The possible solutions for laser parameter improving and optimization are discussed.

Electron paramagnetic resonance (EPR) measurements of CaF₂:Yb (5 mol. %) single crystals were performed for lattice sites substituted by Yb ions and also for the possibility of Yb³⁺ pairs arising. Among eight lines observed in the EPR spectrum, with g = 4.293, 4.1, 3.965, 3.665, 3.433, 3.13, 3.054, 2.894 we think mainly the lines coming from different isotopes of Yb³⁺ isolated ions of cubic symmetry one can distinguish: ¹⁷⁰Yb³⁺ I=0, ¹⁷¹Yb³⁺ I=1/2 and ¹⁷³Yb³⁺ I=5/2, but one can not exclude the lines coming from Yb³⁺ pairs. All of the lines have got an axial symmetry along the crystallographic axis, since the lines do not move with angular variation in the planes parallel and perpendicular to the axis. One can observe also the extra line in magnetic field orientation in every plane at 45°, with the B₀≈191 mT. The unidentified line corresponds to non-axial Yb³⁺ center or unknown impurity. The components of A and g tensors of the spin Hamiltonian for cubic symmetry were calculated. Temperature dependence of EPR lines shows agreement with the Curie law for most of the lines. Peak-to-peak linewidth changes continuously within 20 mT range for "as-grown" crystals, while shows distinct increase above 25 K for γ-irradiated ones. It suggests strong ferromagnetic coupling between neighbours Yb³⁺ and Yb²⁺ ions the latter being created due to Compton electron capture. So, Yb³⁺ co-exists with Yb²⁺ after the Yb³⁺-Yb²⁺ conversion under influence of γ-irradiation and/or annealing in hydrogen. It seems the Yb²⁺ centers arising in CaF₂:Yb (5 mol. %) single crystal after γ-irradiation are related to Yb³⁺, as an effect of recharging one of Yb³⁺ ion from a pair. Absorption measurements of CaF₂ highly doped with Yb³⁺ (0.5 mol. %, 5 mol. % and 30 mol. %) reveal the shifting of the IR maxima of 921 and 980 nm characteristic for 0.5 mol. % doping of Yb³⁺ towards the centrum of IR band (927 and 976 for 30 mol. % of Yb³⁺). Raman spectrum shows localized phonon centered at about 64 cm^-1 being confirmation of the Yb³⁺ pairs presence in the 5 mol. % of Yb³⁺ doped CaF₂ crystal.

Cobalt doped La₃Ga_5.5Ta_0.5O₁₄ single crystal (0.5 mol.% in the melt with respect to Ga) grown by the Czochralski method has been investigated using electron paramagnetic resonance and optical absorption measurements. X- band EPR spectra observed at 8 K under rotation around c crystal axis consists of two asymmetric lines: a narrow line at ~150 mT magnetic field and a second wider line at ~350 mT. These lines could be ascribed to the high spin S=3/2 Co²⁺ ions located at two different crystallographic positions. The low field signal arises from cobalt occupying Ga positions with C₃ symmetry (octaheder), whereas dominating in spectrum, more complicated signal at higher fields arises from cobalt located at Ga positions (tetraheder) with C₂ point symmetry. The whole spectrum repeats every 60° as is expected for trigonal crystal symmetry. Optical measurements have confirmed the conclusion especially for γ-irradiated crystals which reveal additional Co³⁺ content after the treatment. Co³⁺ ions are also seen in "as-grown" (not irradiated) crystals as ⁵T₂-⁵E transition giving absorption bands in the range 700-1100 nm. So in the "as-grown" crystals there arise Co²⁺ ions at octahedral or tetrahedral Ga sites and Co³⁺ ions at octahedral Ga sites.

Electron paramagnetic resonance spectra of La₃Ga_5.5Ta_0.5O₁₄:Ho single crystal for the presence of Yb³⁺ magnetic nonequivalent centers are analyzed. Centers of different symmetries we found two of which being cubic symmetry sites. The existence of the cubic symmetry centers of the Yb³⁺ ions in LGT host crystal confirm that Yb³⁺ ions occupies eightfold coordinated La³⁺ ions. The values of the g-factor for these centers are estimated as: g = 2.059 ± 0.004 (I centre) and g = 2.840 ± 0.015 (II centre). Some results of optical measurements are also presented. They indicate sharp but a weak Yb³⁺ absorption centered at about 978 nm in the IR part of the absorption spectrum, and, equally weak Ho³⁺ absorption in the UV-VIS part of the spectrum (fundamental absorption edge being equal to 250 nm). We think Ho and Yb ions compete in substituting of lattice sites in the crystal. Photoluminescence measurements have shown a very strong signal in the green (533 - 555 nm), slightly less in red (637 - 671 nm) and near-IR (735 - 769 nm) spectral ranges. Co-activation of the Yb-doped crystals with holmium ions leads to appearance of visible luminescence, which is explained by the Yb³⁺-Ho³⁺ stepwise up-conversion mechanism. Additional absorption measurements performed after γ-irradiation with a dose of 10⁵ Gy show wide band originating at 250 nm and extending up to 500 nm (probably due to recharged cation and oxygen vacancies) for both LGT pure and LGT:Yb, Ho single crystals, the lowering of the amount of Yb³⁺ and Ho³⁺ ions (due to Compton electrons capture) and additional absorption band centered at about 600 nm (charge compensating defects) for LGT:Yb, Ho single crystals. Thermoluminescence measurements (TL), does not reveal the presence of any traps in the TL glow curve.

The characteristics of a Q-switched neodymium-doped double-clad fiber laser were presented. Based on the proposed differential equations with suitable boundary and initial conditions, a numerical model was developed to simulate this fiber laser. All the calculations were based on wave-travelling approach. Using this model, pulse duration and the energy of generated pulses can be predicted. In the experiment, pulses with the energy of 0.36mJ (84ns) and 154μJ (48ns) at the repetition rate of 500Hz were achieved for 5 and 3-m long fiber, respectively. The extractable energy was limited due to low energy storage and the fiber-end facet damage. The results obtained numerically agree well with the experimental results.

Growing application of solid state lasers brings the requirements of new wavelengths generation together with a compact simple construction of laser system. We have demonstrated compact, diode pumped Nd:YVO₄/LiF:F₂- nanosecond laser source operating simultaneously at 1064 and 1143 nm wavelengths. The laser based on Nd:YVO₄ crystal gives an efficient output and offers various options for wavelength conversion. The LiF:F₂- crystal inserted inside the resonator plays dual role of passive Q-switch for Nd:YVO₄ laser, and gain medium of color center oscillator. The 52 mm long cavity consisted of 0.25% Nd³⁺ doped YVO₄ and LiF:F₂- crystal of 40% initial transmission. The resonator output coupler with curvature radius of 150 mm has 5% and 15% transmission at 1064 and 1150 nm wavelengths, respectively. The rear mirror was HR for both wavelengths and AR for 810 nm diode pumping (20 W diode bar with beam shaper). The linear polarized at both wavelengths output pulses with the energy 6 and 2 μJ at 1064 nm and 1143 nm, respectively, were detected. The corresponding pulse length (FWHM) was 6.5 ns and 4.5 ns. The pulse frequency at each wavelength was about 75 kHz. The 15 nm width of spectrum centered at 1143 nm wavelength was measured. The multimode output with divergence angles of 5.2×3.5 mrad was evidenced. The pump threshold was about 6 W and maximum mean power was 0.145 W for 18 W pump power with duty factor of 25%. This laser could be used for spectroscopic and other applications.

In this paper we report on a record 1.4 MW peak power, actively Q-switched Er:YAG laser operating at 2.94 μm. As a result of our experiment, at 3 Hz repetition rate, we achieved 91 ns pulses with 137 mJ energy. At higher repetition rate (10 Hz) the laser generated 100 ns pulses with 35 mJ energy. These results, according to our knowledge, are the best that have been ever achieved.

Most of the work on passively Q-switched microchip lasers emitting at 1064 nm has been done with neodymium-doped YAG crystals as gain material and Cr⁴⁺:YAG as saturable absorber. The bulk Cr⁴⁺:GGG Czochralski grown passive Q-switches were also investigated. We have used a technique of liquid phase epitaxy (LPE) to grow Cr⁴⁺:YAG, Cr⁴⁺:GGG and Co²⁺:YAG thin films of saturable absorber. X-ray diffraction analysis, optical transmission spectra measurements and passive Q-switching experiments were performed to characterize the obtained layers. Absorption saturation measurements of Cr⁴⁺:YAG, Cr⁴⁺:GGG and Co²⁺:YAG layers were carried out at 1.06 μm and 1.54 μm, respectively.

The paper presents application of laser radiation for cleaning of monuments and art works, using Q -switched Nd:YAG laser generating high power series of pulses in so called "burst mode". The time width of pulse train is 200 ÷ 300 μs. The oscilloscope traces of pulse repetition frequency and the results of energy measurements are shown. Numerical model of interaction of high power laser pulse with graphite layer of aluminium substrate on the base of equations in one-dimensional hydrodynamic approximation is presented. The results of calculations of graphite removal process for single pulse and train of laser pulses are in qualitative agreement with the results of measurements.

We present the fabrication of waveguides by laser ablation of metal targets on pyrex glasses. An horizontal position of the sample and the plate was found suitable to improve the effect of the plume in the sample with respect to the alternative vertical arrangement. We have analysed the longitudinal and transversal profiles, using a profilometer and have compared the results for the different configurations, speeds and metal targets. We show pictures of the surfaces, obtained by electron microscopy and confocal microscopy. We have studied the characteristics of the structures taking account the optical and thermal properties of the metal foils.

We report about theoretical results and experiments, which led to the demonstration of optical bistability on the specially modified laser diode (LD) created on the double heterostructure Ga_1-x Al_xAl/GaAs with saturable absorption section. To prove the bistability, the time method for bistability impulse verification (BIV) by bistable laser diode (BLD) was proposed. With the use of the BIV method, basic parameters of the hysterisis loop of the W-A characteristic samples of realized BLD were determined. Also the mathematic model of the W-A characteristic was derived, used for the simulation of the characteristic for the realized BLD. Element values of the electrical equivalent circuit of the BLD for small changes of signal were calculated for selected operating points of the simulated W-A characteristics. The dependency of bistability on the temperature is monitored by measuring the BLD W-A characteristic.

External cavity lasers (ECLs) have been around for many years and are recognised as useful tunable narrow line light sources. In this communication we present space resolved spectral characteristics of the ECLs with a standard glass grating and ridge-waveguide broad-contact optical amplifiers (SOAs). The gain of the SOAs was centered in the range of 960 to 980 nm. The spectral characteristics have been measured with an optical spectrum analyzer. The results are compared with the ones obtained after the glass grating was substituted by a grating made from silicon. Application of such silicon gratings can be considered as a first step towards ECLs made fully in a MEMS configuration.

We report on novel evaluation methodology of high-power diode lasers that potentially will increase the reliability level of these devices. The study is carried out for wide-stripe, 808 nm diode lasers with low fast-axis beam divergence that base on a double-barrier single quantum well separate confinement heterostructure. The diodes are assembled in standard packages with base diameter &slasho; = 9 mm. Degradation of diode lasers is a result of the interaction between internal and external factors. Thus, insight into degradation mechanisms is only possible with a complex characterization of the devices. In our analysis we involved standard measurements such as current-voltage, light-current characterizations, as well as advanced methods such as high-resolution thermography. The latter one allows for investigations of thermal properties of diode lasers including fast temperature profiling and defect recognition. We discuss the usefulness of above techniques for screening purposes. Finally we present results of reliability tests of the diode lasers. A correlation between initial tests and lifetest results is shown.

This present work concerns the growth and the characterization of Co₂MnSi thin films deposited onto GaAs substrates. Two PLD configurations have been explored, the conventional 1-Beam-PLD and the 2-Crossed-Beams-PLD one. We demonstrated that, with 1B-PLD conditions, we got Co₂MnSi polycrystalline structure with unwanted droplets. The 2CB-PLD allowed us to get droplet-free, single crystalline thin films at substrate temperature as low as 353 K.

Refractive index knowledge is one of important parameter when physical properties of materials are investigated. It is also known that temperature variation and wavelength are also effect on the measurement results when materials are characterized. Therefore fast and accurate measurements are needed to measure especially refractive index properties of material. In order to cover this poverty we established we established a computer controlled an optical facility in National Metrology Institute of Turkey, based on laser beam displacement technique. Basic components of established facility are laser sources, sample holder, knife-edges and detectors. In order to compensate fluctuations arising from laser instability we used electro optic modulator that kept the intensity of lasers stable at around 10^-5. A temperature controlled sample holder was used to measure temperature dependence of materials. The displacement of laser beam was determined using knife-edge, which moved using a computer controlled servomotor. The refractive index than was found from displaced laser peak signal using designed trap detectors based on three single-element silicon photodiodes.

When a probe confined in a single focused laser beam approaches the surface, it is getting more influenced by the retroreflected beam. This beam interferes with the incident one and a weak standing wave (SW) is created, which slightly modulates the incident beam. We studied experimentally how this phenomena influences the optical trap properties if SW is created using surfaces of two different reflectivities. We used polystyrene probes of diameters 690 nm and 820 nm, tracked their positions with quadrant photodiode (QPD) and analysed their thermal motion to get the axial trap stiffness along optical axis.

In order to measure small diffusion coefficients of miscible fluids, in this paper we propose an improved version of digital projection moiré. The system uses a simple and flexible fringe generator realized by means of a video projector with a modification of projection optic. The fringe patterns are projected on the bottom of a ground glass plate. The phase object (diffusion cell) is placed in front of the ground glass (in other words, in front of the fringe pattern), which is imaged by a digital video camera. Grating patterns, during the evolution of diffusion phenomena, are captured by a CCD camera and stored in a computer at different times. With the aid of signal demodulating techniques, the images are processed to obtain the diffusion coefficients. The theoretical aspects of the method are presented and the relationship between the fringe shift and the diffusion coefficient is derived. Furthermore, we report some experiments conducted for demonstrating the usefulness of the system.

Ultrasonic motors have seen application in areas needing compact, efficient, and intermittent motion. Such applications include: camera auto focus lenses, watch motors, compact paper handling, microrobots, medicine and etc.. They are characterized by high torque at low rotational speed, simple mechanical design and good controllability. Compared with electromagnetic actuators, there is no danger of interference due to electromagnetic induction because no magnetic field is used and ultrasonic motors are more quiet since speed-reduction gears are not required. A polarization vector of the piezoceramic element and location of excitation electrodes on its surface determine the resonance modes of the high frequency vibration exciter. In its turn the modes of vibration play a key role in the functionality of ultrasonic motor. There are analyzed two different regimes of operation--when the contact zone of the resonator performs elliptic and unidirectional motions. Though the mechanical characteristics of the ultrasonic motor in both cases are comparable, detailed analysis of the contact surface shows very different wears. Laser holography is used to identify and control the regimes of motion of actuator. Experimental results are compared with computer simulations. Contact surfaces are analyzed by atomic force microscope (AFM) before experiment, after 10 minutes and after 50 minutes of operation.

In this paper, a novel measurement of FM-noise is shown. We present both experimental and simulation results by considering the external RF phase modulation, with good agreement. The results show for the first time, the influence of the phase modulation index, modulation frequency, in the conversion of FM-noise to intensity noise in an optical link by considering all effects on RF modulated light emitted by a 1550 nm DFB laser.

In this work we focus on an analysis and a comparison of different, both multi-photon and multi-ion excitation mechanisms which can be used for pumping of a short wavelength neodymium doped ZBLAN fiber laser. Spectroscopic properties of Nd:ZBLAN examined under various excitation conditions enabled identification of the involved processes. Rate equation based models have been developed and employed to compare the efficiency of main excitation schemes, giving a good starting point for further optimization and development of Nd:ZBLAN up-conversion fiber laser.

High power widely tunable lasers are extremely desirable for telecom applications as a replacement for distributed feedback (DFB) lasers in wavelength division multiplexing (WDM) systems, due to their dynamic provision properties. They are also sought after for many other applications, such as phased radar systems, optical switching and routing. This paper introduces novel design ideas and approaches on how to achieve ultra high power in the design of an InGaAsP-InP based widely tunable laser gain section. The inventive ideas are basically composed of two parts. Firstly, to increase the facet optical output power by the inclusion of an InP spacer layer below the ridge and above the multiple quantum wells (MQWs) stack, in order to have extra freedom in the control of widening the single mode ridge width. Secondly, to reduce the free-carrier absorption loss by the inclusion of a bulk balance layer structure below the MQWs stack and above the buffer layer, so as to largely shift the optical mode distribution to the intrinsic and n-doped side of the epilayer structure where the free-carrier absorption loss is lower than that of the p-doped side. Simulation results show that the proposed epilayer designs of the ultra high power gain sections would greatly increase the facet optical output power of a tunable laser, by up to about 80%. It should be noted that these novel epilayer design ideas and approaches developed for the gain section are applicable to the designs of ultra high power DFB lasers and other InGaAsP-InP based lasers.

In this work we present our theoretical investigations on optimization of double doped up-conversion fiber laser, operating in the visible part of spectrum. The developed mathematical model, based on measured spectroscopic parameters, enables analysis of influences of the active fiber and resonator parameters on the threshold and above-threshold laser characteristics. In particular, we discuss the behavior of output power versus the pumping power and mirror reflectances for the basic optical transitions in praseodymium ion, corresponding to the lasing in red, green and blue range.

The results of the spectral and spatial measurements of a laser-produced (LPP) plasma source of extreme ultraviolet (EUV) for 13.5 nm are presented. The double stream Xe/He gas puff target in the source was utilizing. The source was equipped with a Nd: YAG laser system (E = 0.55 J, t = 3.9 ns, f = 10 Hz, M² = 2.5) and was dedicated to EUV metrology purposes. An advantage of this approach of the laser-plasma source is a debris free EUV emission. For the spectral research a transmission grating spectrograph (TGS) and a grazing incidence spectrograph (GIS) were utilized. For spatial measurements a pinhole camera was employed. The influence on EUV emission of the laser focal spot position in relation to the gas puff target and the time delays between opening valves and the laser pulse were investigated.

Effects of process parameters on pulsed laser deposition of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) were studied. Process parameters like laser energy and ambient atmosphere influence both the expansion dynamics of a laser ablated plasma plume and topography of deposited layers. The plume created using 193 nm, 20 ns pulses from ArF laser was analysed by means of space and time resolved optical emission spectroscopy. The velocity of the plasma plume at several distances from the target in different ambient conditions was determined. The deposited hydroxyapatite layers were analyzed by means of atomic force microscopy and X-ray diffractometry in order to determine the film topography, its structure and mechanical and physical properties. The results show that the plume expansion velocity as well as the topography of deposited films depend on the sort of ambient gas and its pressure.

Significant progress observed in last years in structure and technology of ion laser discharge tubes created new possibilities of the continuous generation of the ultraviolet radiation. Segmented metal-ceramic laser discharge tube was used in our experiments. CW generation of 3 new UV lines in double ionized argon and krypton was observed. Generation of two of these lines (Ar III, λ=350.4 nm and Kr III, λ=330.4 nm) was unknown up today even in high current pulse operation. The shortest (λ=324.8 nm) Kr III line, well known in pulse mode but unknown in CW operation is particularly important. Relatively low threshold current and comparable with known Kr III (337 nm) output power level makes easy its application. Laser UV operation on the mixture of two most important, active gases Ar and Kr were studied. Simultaneous generation of the all laser lines of Ar III and Kr III was achieved. For the optimal mixture composition relatively high power generation of 10 laser lines in a wide spectral range 324 - 363 nm were obtained. Preliminary experiments on determining the influence of high ionization potential inert gases (Ne, He) on the UV generation in the argon were carried out. Advantageous influence of Ne results on the distinct increasing of the laser power and similar distinct lowering the threshold current of the generation was observed.

The luminescent method was used to measure the spectrum of turbulent pulsations of gas density in fast- axial flow CO₂ laser with radio-frequency discharge input. It is shown that gas density pulsations increase through gas discharge along gas flow axes. In continuous-wave fast-axial flow (FAF) CO₂ laser there is subsidiary deterioration of quality of active medium due to intrinsic turbulence intensified by gas discharge energy input.

Recent experimental results on new all gas-phase chemical generation of atomic iodine via atomic fluorine for a Chemical Oxygen-Iodine Laser (COIL) are presented. Advantages of this method are emphasized in comparison with the conventional use of molecular iodine as a precursor of atomic iodine for lasing. Fluorine atoms are produced by fast reaction of molecular fluorine with nitrogen oxide and then react with hydrogen iodide to atomic iodine. Reaction conditions and the most convenient experimental arrangements were searched for their application in the supersonic COIL. An inevitable instrument used in this investigation was the optical Iodine Scan Diagnostics (ISD) of generated atomic iodine, based on the tunable diode probe laser. Concentration of atomic iodine was mapped by this method in the reactor at different experimental configurations, pressure and concentration of reactants. This research supported by mathematical modeling revealed that, the best arrangement would be generating atomic iodine in a separate reactor and injecting it into the singlet oxygen flow in the COIL.

Argon and krypton ion lasers work typically in CW (continuous wave) mode. In many of applications, the continuous operation of ion lasers is not required. Presented in this article laser power supply makes possible to operate in two regimes: continuous and quasi-continuous (multi-pulse). In multi-pulse operation the most of output power limits for continuous regime was overcame. This allowed increasing the laser output power considerably. Particularly excellent results were obtained for laser tube filled with Ar-Kr mixture and operating in UV range. The main phenomenon deciding on output laser power increasing in pulse and multi-pulse operation is minimization of harmful effects of gas pumping. Possibility of multi-pulse operation creates new advantages of ion lasers and extends range of its applications.

We describe a general way how to calculate optical forces and torque acting on colloids placed into laser interference field. In this paper we focus on a configuration with three interfering beams laying in one plane and we present a comprehensive analysis of trap properties and particle behaviour. We found that this arrangement can be used for sorting of particles according to their size or refractive index.

At the present time the methods of the gas assisted laser cutting (GALC) of the different steels (alloyed and non-alloyed) and also of non-ferrous metals, such as Al and Ti, using one of the inert gases (nitrogen, argon, helium) or the active gas (oxygen) or air as assist gas are widely spread. However these cutting methods have the series of essential shortcomings. Heaving performed the theoretical and practical investigations of the mentioned methods we concluded that the great interest is the use of mixtures containing inert gases and oxygen with controlled concentration. The application of such assist gas mixtures permits the laser cutting velocity to be increased as against the use of pure inert gas. The chose of optimal oxygen concentration leads to reduction of expensive gases consumption and makes the cutting process cheaper.

For the laser drilling of aluminum nitride (AlN) ceramic the influence of the laser parameters and material properties on the drilling rate, quality of the holes and the effects related to plasma formation are investigated. The ablation is performed by pulsed irradiation of Nd:YAG laser at wavelengths of 1064, 532 and 355 nm, at pulse duration of 6 ns (FWHM) in air. The SEM scans of the processed surface reveal regular, cylindrically shaped holes of diameter of about 100 μm obtained under conditions of constant fluence at all wavelengths applied. Holes are surrounded by circular zones which are colored different than the non-processed surface, and of a much larger diameter. Comparison of the original material composition with that of the processed one made by EDX shows a decrease of the N concentration in the affected area. The zones are identified as heat-affected due to the high thermal conductivity of the ceramic material and change of the photon distribution due to multiple reflections into the material. In the LIBS spectra recorded in order to obtain the composition of the ablated material the presence of ions and neutrals depends on the laser intensity applied. At intensity values close to the ablation threshold the ejected material consists mainly of neutrals and doubling the intensity results in appearance of single-ionized Al species. The ionized species dominate over neutrals under conditions of higher drilling rate (15 GW/cm² at 532 nm). Their existence in the plasma plume together with clusters is confirmed by the TOF-MS spectra. It also corresponds to the characteristic spatial structure of the plume. The investigation of the decomposition reactions of AlN in dependence on the applied laser intensity is based on numerical solving of the three dimensional heat-transfer equation. A solution consistent with the experimental observation indicates that at threshold the ceramic decomposes into gaseous nitrogen and solid Al particulates, while at higher fluences the Al vaporizes and influences the drilling quality.

Semiconductor lasers, which can be surely characterize by many of their advantages, have been used for measurements of concentration of gases for many years. Doing measurements in industrial conditions, because of its several difficulties, needs using special technology of measurements. In this article using modified, correlated absorption spectroscopy, in order to measure CO concentration, has been shown.

The increasing demands for miniaturization and better functionality of electronic components and devices have a significant effect on the requirements facing the Printed Circuit Board (PCB) industry. PCB manufactures are driving for producing high density interconnect (HDI) boards at significantly reduced cost and reduced implementation time. The interconnection complexity of the PCB is still growing and today calls for 50/50 μm or 25/25 μm technology are real. Imaging of HDI boards poses a rapid increasing challenge on PCB manufactures due to line width and space getting smaller and mainly to tighter registration requirements. Existing technologies are unable to offer the acceptable solution. Nowadays the Laser Direct Imaging (LDI) technology is considered as an answer for these challenges. LDI is a process of imaging circuitry pattern directly on the PCB without the use of a phototool. The exposure of the photo-sensitive resist is carried out using a laser beam that is scanned across photoresist surface and switched on and off by means of a computer control system according to the electrical circuit pattern. Usually the laser used in the LDI generates the UV line, which is suitable for the commonly available photoresists. In this paper we present an introduction to LDI technology as well as an experiment consisted in an attempt to use a UV Nd:YAG laser (λ=355 nm) for direct imaging of conductive pattern on the PCB covered by photosensitive resist.

Techniques of laser emission spectroscopy such as LIPS and LIF are applied to identify pastels and pigments composition for the use in conservation of historical documents. The question of data reliable for pigment identification by these techniques is considered. For model samples made of the cotton paper of chemical composition corresponding to the historical ones, and coated with pastels of different colors the LIPS and LIF spectra are recorded. Samples are excited by the pulsed Nd:YAG laser operating at 355 or 266 nm. The reference Raman spectra are collected, too. Bands characteristic for the blue pigments: PB15, PB29; violet one PV16, and yellow PY 184 are identified exclusively by LIPS in agreement with literature. Also additives such as the barium white found in the Scarlet pastel, and ultramarine (Na_8-10[Al₆Si₆O₂₄]S_2-4) with titanium white (TiO₂) in the Phthalo Blue are identified, and confirmed by the Raman technique as well. The pigments anthraquinone (PR 168), isoindolinone (PY 110) and monoazo (PY 74) are not revealed. In the LIF spectra only a broad band centered at 612 nm and corresponding to anthraquinone (red pastel) can be clearly assigned.

For the Gotlandic sandstone samples extracted from historical monuments and covered with model encrustation the effect of pulsed, ablative laser cleaning at 1064 nm on the surface discoloration was investigated for the irradiation in ambient air and in the N₂ flow at various velocities. The colorimetric data of a sufficiently large sample population were measured. A slightly stronger decrease in the surface lightness for the artificially coated and also pure substrate samples irradiated in nitrogen compared to the ambient air case were observed. This difference was ascribed to material oxidation and partial combustion of surface remnants due to presence of O₂ contributing to the final effect of laser cleaning.

Laser glass marking is currently used in several glass materials for different purposes, such as bar codes for product tracking, brand logos or just decoration. Systems with a variety of different laser sources, with inherent power ranges, wavelengths and pulse regimes have been used, namely CO₂, Nd:YAG, Excimer, Ti-Sapphire lasers. CO₂ Lasers systems, although being a reliable tool for materials processing, and very compact in the case of sealed low power lasers, are usually associated with a localized thermal loading on the material, causing brittle materials like glass to crack around the irradiated area. In this experimental study a pulsed CO₂ laser was used to direct marking the glass surface. The temporal characteristics of the laser pulse--pulse length, period and duty cycle were varied, and glass materials with different thermal properties were used in order to correlate the marking process--cracking or softening with or without material removal with the laser and material characteristics. Glass materials with major industrial application, such as soda-lima, borosilicate (PYREX) glasses and crystal have been investigated. Laser marked areas have been characterized in terms of surface optical properties, like diffuse and direct reflectance and transmittance for white light, directly related with marked surface quality.