This PDF file contains the front matter associated with SPIE Proceedings Volume 9266, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Applying the self-diffraction process to clean ultrashort laser pulses temporally is a recently developed effective way to temporal contrast enhancement. In this paper, we attempt to clean ultrashort laser pulses temporally by the self-diffraction process. Experiments were carried out to study the temporal contrast improvement in the front-end system of an ultraintense and ultrashort laser facility, i.e. the super intense laser for experiment on the extremes (SILEX-I). The results show that the maximum conversion efficiency of the first-order self-diffraction (SD1) pulse is 11%. The temporal contrast of the SD1 signal is improved by two orders of magnitude, i.e. to 103, for a 2.4-ns prepulse with initial contrast of ~10. For a 5.5 -ns prepulse with initial contrast of 2×103, the temporal contrast of the SD1 signal is improved by more than three orders of magnitude.

We experimentally show a method for pulse-width measurement. Pulse widths at different partial positions of an ultrashort-pulsed beam are measured, results show that pulse widths in the center of the beam are less than that of in the edge because of the existence of residual chirp. We also investigate the temporal evolution at a strongest spatial modulation position of the beam during small-scale self-focusing, it finds that its pulse width decreases as power increases due to a spatiotemporal coupling effect. We find that this method not only can be used to accurately measure the pulse width at any one spatial position of the beam, but also be useful for real-time monitoring of spatial-temporal evolution.

In extremely intense laser system used for plasma physics experiments, temporal contrast is an important property of the ultra-short pulse. In this paper, we theoretically study the temporal contrast degradation due to wave front deviation in large aperture ultra-short pulse focusing system. Two-step focusing fast Fourier transform (FFT) algorithm with the coordinate transform based on Fresnel approximation in space domain and Fourier integral transform method in time domain were used to simulate the focusing process spatially and temporally, in which the spatial distribution of ultra-short pulse temporal contrast characteristics at the focal spot is related to the wave front in large aperture off-axis parabolic mirror focusing optical system. Firstly, temporal contrast degradation due to wave front noise with higher spatial frequency is analyzed and appropriate evaluation parameter for large aperture ultra-short pulse focusing system is put forward from the perspective of temporal contrast. Secondly, the influence of wave front distortion with lower spatial frequency on temporal contrast is revealed comparing different degradation characteristics of various aberrations. At last, a method by controlling and optimizing the wave front to prevent temporal contrast degradation in large aperture ultra-short laser system is proposed, which is of great significance for high temporal contrast petawatt laser facilities.

SG-III laser facility is now the largest under-construction laser driver for inertial confinement fusion (ICF) research in China, whose 48 beams will deliver 180kJ/3ns/3ω energy to target in one shot. Till the summer of 2014, 4 bundle of lasers have finished their engineering installation and testing, and the A1 laser testing is undergoing. A round of physics experiment is planned in Oct. 2014 with 5 bundle of lasers, which means the facility must be prepared for a near-full-capability operation before the last quarter of 2014. This paper will briefly introduce the latest progress of the engineering and research progress of SG-III laser facility.

Laser-induced static surface shape changes of deformable mirrors will cause difficulties for beam control of the laser system. The overall peak and valley (PV) value of the deformable mirror (DM) will reach the scale of micrometer when irradiated by high power lasers. We have investigated changes in the static surface shape of a 37-element DM caused by laser-induced thermoelastic deformation. It is found that the laser-induced profile change of the mirror shows a high-order characteristic. In this paper the finite element method is used to analyze the surface shape of the DM when it is irradiated by high power lasers. The surface shape is fitted using the Zernike polynomials and the influence functions to see the characteristic of it and the DM’s ability to compensate it. The fitting results show that the lower-order aberrations can be corrected by the DM itself with the cost of a reduced ability of aberration correction, as the available amount of stroke will decrease. In addition, changes of the influence functions are simulated and the modified influence functions are calculated. Furthermore, the performances of the DM in three different situations are simulated to reveal the impact of thermoelastic deformation on the DM’s aberration correcting ability.

Laser-induced damage (LID) to optical glass has become a growing problem in high-power laser systems. It is well known that the main reason of glass being damaged is due to defects and impurities in the material. Damage caused by subsurface defects (SSDs) is especially common in actual system running. Accordingly, in the presence of SSDs, a simple and alternative calculation method is developed to evaluate the enhancement of light field around the incident and exit surface. This ray tracing approach, based on the classical optics theory, is very direct and clear to show the optical phenomena of light intensity enhancement. Some basic SSD shapes have been studied and investigated here, which reveals the importance and boundary condition of controlling the size and density of SSDs in grinding and polishing process. Finally, to achieve optimal breadth depth ratio, the least etching amounts by hydrofluoric (HF) acid is investigated. The theoretical analysis and simulation results provide an appropriate range of removal amounts, which is very important in the HF etching process.

In high power laser systems, nonlinear effect, one of the key factors of beam wavefront aberration and even irreversible damage to system, has always been one of the top considerations of researchers for decades. A hybrid ray-tracing method for both linear media and nonlinear media based on geometric optics is presented in this paper and realized by programming. In a simple optic system with KDP crystal, an obvious decline of beam quality is observed in high laser power density conditions and a method taking component intervals as compensation of beam quality is proved feasible. Considering the complexity of traditional modeling method based on surfaces, a modeling method based on components is established. Hopefully, the conclusions and flaws of this paper can shed light on relevant work and further research.

High-power laser systems are getting more and more widely used in industry and military affairs. It is necessary to develop a high-power laser system which can operate over long periods of time without appreciable degradation in performance. When a high-energy laser beam transmits through a laser window, it is possible that the permanent damage is caused to the window because of the energy absorption by window materials. So, when we design a high-power laser system, a suitable laser window material must be selected and the laser damage threshold of the window must be known. In this paper, a thermal analysis model of high-power laser window is established, and the relationship between the laser intensity and the thermal-stress field distribution is studied by deducing the formulas through utilizing the integral-transform method. The influence of window radius, thickness and laser intensity on the temperature and stress field distributions is analyzed. Then, the performance of K9 glass and the fused silica glass is compared, and the laser-induced damage mechanism is analyzed. Finally, the damage thresholds of laser windows are calculated. The results show that compared with K9 glass, the fused silica glass has a higher damage threshold due to its good thermodynamic properties. The presented theoretical analysis and simulation results are helpful for the design and selection of high-power laser windows.

The uniformity measurement, transmittance and reflectance of the optics in other words, is one of the essential specifications for those large optics of high power laser facilities. Both high reproducibility for large-size and precision with wide dynamic range make such testing a real challenge to take. In this paper, a transmittance and reflectance measurement system with large aperture is demonstrated. With a laser source at 1053nm, three kinds of large aperture optics are tested by conventional direct detection. The results show that this system can realize high measuring precision (0.05% and 0.01% for transmittance and reflectance respectively) when tested parameter is small in value. In addition, the measurements precision with 532nm and 351nm laser sources are also tested compared, and the factors of measurement uncertainty with shorter wavelength are analyzed. To further promote accuracy and signal-noise ratio, coherent heterodyne detection and optical demodulation technique is proposed especially for high transmittance measurement. A demonstrative experiment of transmittance detection by balanced heterodyne and optical demodulation is performed, and a SD=0.052%, which is more than two order precision is achieved. It results that it is valid compared with conventional direct detection, and gives a promising method for higher precision during further practical applications.

S-band fiber lasers, one type of ytterbium doped fiber lasers(YDFLs) which emitting in the spectral region of 1010 nm ~ 1050 nm, have drawn more and more attention especially after the proposition of tandem pump fiber lasers. The S-band laser plays an important role as the pump in a tandem pumping scheme. However, high power S-band laser output is quite difficult because of severe re-absorption. Therefore, the optical properties of S-band fiber lasers are studied and methods to achieve high power S-band laser output are presented. An S-band laser emission model based on gain comparison is built for analyzing the mechanism of laser oscillation and amplification. The model is composed of rate equations and gain comparison of several wavelengths in ASE spectrum. The gain differential between laser wavelength and ASE peak wavelength is compared to the additional gain imposed by cavity mirrors in an oscillator or the seed in an amplifier. The comparison results help in concluding the feasibility of S-band laser emission. Based on the model, the influences of fiber properties (including core doping level, core -clad ratio, and fiber length), pump power and laser power on the operation of S-band fiber lasers or amplifiers are researched. The analysis shows that fibers with lower doping level, larger core-clad ratio and shorter length, seed with higher power, are more helpful in realizing high power S-band laser output. Also, the profile of oscillator is found more suitable in building high power S-band lasers than that of amplifier.

Strong water absorption at 2 μm generated recent interest in lasers at this wavelength for soft tissue surgery. A fiber Bragg grating-based, all-fiber, continuous-wave, cladding pumped, thulium-doped fiber laser at 1.95 μm is configured. The thulium-doped active fiber with octagonal-shaped inner cladding is pumped at 808 nm (total power of 17 W) with six laser diodes through a combiner. The laser power of 3.3 W (after elimination of unabsorbed pump power through a passive fiber) with slope efficiency of 23% (against launched pump power) is achieved. The linear variation of laser power with pump offers scope of further power scaling.

In high power fiber laser, the limiting factor of narrow linewidth output is analyzed. The influence of Stimulated Brillouin scattering effect and sinusoidal phase modulation suppressing method are studied. The linewidth of a single frequency laser is broadened from 1MHz to 2.9 GHz by sinusoidal phase modulation technology. The output power of single frequency laser is 50mW. And through three stage fiber amplified, the central wavelength of 1064.34nm, linewidth of 2.9 GHz and power of 780W are achieved respectively. The optical-optical efficiency is 79%. And the beam quality is [see manuscript] and [see manuscript]. The distributing characteristic of longitudinal mode, under every modulating coefficient, is measured. And the result is the same as theoretical result. The increasing of longitudinal mode number, controlling of longitudinal mode spacing and reducing power spectrum density by sinusoidal phase modulation are proved to be viable. Then Stimulated Brillouin Scattering threshold is increased. Finally, the output power is increased a lot. The output power of this laser is only limited by pump power. If the pump power is increased, the higher power of narrow linewidth fiber laser will be achieved.

We present novel and powerful pump schemes for fiber laser sources operating near 2 μm, which employing high power Raman fiber lasers (RFLs) to provide sufficient pump light. Firstly, we demonstrate a Tm-doped fiber laser (TDFL) pumped by two RFLs at 1173 nm. The output power of the TDFL reached 96 W with slope efficiency of 0.42, and the central wavelength located at 1943.3 nm. This is the first TDFL with 100 W-level output power pumped by RFLs around Tm³⁺ ions’ ~1200 nm absorption band. Secondly, we demonstrate a Ho-doped fiber laser (HDFL) employing a 1150 nm RFL as pump source. The 1150 nm RFL provided 110 W pump power and the output power of the HDFL reached 42 W with slope efficiency of 0.37. The lasing wavelength covered from 2046.8 nm to 2049.5 nm with optical signal-to-noise ratio more than 30 dB. This is the first HDFL pumped by a 1150 nm RFL and the highest output power achieved at this pump band. In the last, we present a high power Ho-doped fiber (HDF) superfluorescent source (SS) pumped by a 1150 nm RFL. The SS’s output power reached 1.5 W, and the full width at half maximum was about 30 nm. This is the highest output power achieved in HDF as far as we know. The results above indicate promising and powerful pump schemes to achieve higher power output in fiber lasers near 2 μm, which also can be further improved by optimizing the parameters of the sources.

We report on the construction of a pulse-pumped fiber laser using highly doped gain fiber within a ring-shaped all-fiber resonator. The pump laser is pulse modulated and coupled into a segment of highly doped Erbium doped fiber. The ring cavity is close-looped in an all-fiber manner. The pulsed-lasing in kHz repetition rate down to single-shot operation are tunable by pulsed-modulation of the pump laser and tuning of an intracavity variable optical coupler. The lasing power increases for a higher pump pulse energy and repetition rate which sets the limit of the output pulse energy. We measure the time-domain characteristics of the lasing pulses and analyze the dynamical property of the pulsed-pumping process theoretically based on time-dependent rate equation.

Study on random laser is an interesting topic in physics. In this paper we pay much attention to the high power random laser achievement in optical fiber. Two kinds of optical gains are used for light amplification. One is Raman gain and the other is Yb-doped fiber gain. The random signal is provided by distributed feedback came from Rayleigh scattering and amplified by those gain. We obtain the highest random laser output power results and different laser emitting characters are also reported.

We report a generation of 10.6% conversion efficiency near 1053 nm first order Stokes pulse in stimulated Raman scattering pumped using 800 nm Ti:sapphire based femtosecond pulses that are stretched to 460 ps, obtained by use of a single pass ethonal Raman shifter. The Stokes pulse almost maintains the bandwidth of the pump and is compressed to ~10 ps using a mismatched grating-pair. The spectral characteristic of the Raman pulse is calculated and the results explain the observed transient features.

The combination of volumetric heating of the laser material by the absorbed pump radiation and surface cooling required for heat extraction leads to a no uniform temperature distribution in the rod. With the coactions of pump field and coolant, the temperature gradient is formed within laser working medium, and then the thermal effects including thermal lens, thermal stress birefringence, etc. They all seriously restrict the output characteristics of laser. The uniform temperature field distribution in laser working medium weakens the influences of thermal effects in laser. The thermal effect of Tm:YAG laser generated by laser-diode pumping the Tm:YAG crystal is analyzed. After considering the quasi three-level structure of the crystal and the distribution of transmission power in the cavity, a more actual temperature field in the crystal is obtained by revamping the heat conversion coefficient. The thermal effects mechanics were analyzed at first, and then the physical and mathematical thermal analysis models were established based on the theoretical knowledge of thermal effects in LD pumped Tm:YAG laser. The method can be applied to the laser thermal effect research of quasi three-level. The analysis and the result can be referred to the thermal effect research of the solid state laser end-pumped by the LD and the optimal design of resonant cavity.

High power single-mode ridge waveguide 1060-nm semiconductor lasers are reported. The lasers consist of compressively strained double InGaAs/GaAs quantum wells and a GaAs/AlGaAs separate confinement vertical structure. A super large vertical optical cavity is employed to have a low internal loss, large optical spot size and low vertical optical divergence angle. The material composition and thickness of waveguide layers and claddings layer are optimized systematically. The active layer is detuned from center of the waveguide and thickness of cladding layers is optimized to guaranty single mode lasing of the large optical cavity. The large vertical cavity laser structure with thickness of 4 μm allows the lasers have a low internal loss of less than 0.6 /cm, a large optical spot size about 1μm and a vertical divergence angle about 20 degree. For lateral optical confinement, a double trench ridge waveguide is employed to maintain single-lateral-mode operation. Based on the optimization, 1.5 W continue wave optical power is achieved for broad area lasers with 1mm longitude cavity length. Narrow stripe ridge waveguide lasers of 1mm cavity length with single mode current and optical power of 700 mA and 340 mW is obtained. Suggestions for further improvements in terms of single mode power and applications of the high power semiconductors are discussed.

A diode-pumped alkali lasers (DPAL) is a new type of laser source which can offer laser radiation with high efficiency and tiny thermally-induced effects in the near-infrared wavelength region. By constructing a theoretical algorithm through uniting the kinetic, heat transfer, and fluid dynamic procedures together, the thermal features and output characteristics of a DPAL are systematically evaluated for both the static and flowing-gas statuses. The corresponding temperature distributions are calculated for different powers of a pump beam. The results are thought to be useful for realization of a high-powered DPAL in the future.

A compact, high power and high beam quality laser diode stacks partially end-pumped quasi-continuous wave slab laser with hybrid resonator is demonstrated. Using this configuration, with Nd:YVO₄ as the slab gain media, 101 W output power is obtained when the pumping power is 216.5W with the repetition of 1kHz, the optical-to-optical efficiency and slope efficiency are 46.7% and 51.14%, respectively. The beam quality M² factors in the unstable direction and the stable direction are 1.36 and 1.56 respectively at the output power of 101 W.

In the Tm³⁺ doped YAG crystal, the Tm³⁺ ions are excited into the ³H₄ state from ³H₆ state by absorbing pump radiation at ~ 785 nm, and the ions then relax down to the upper lasing level ³F₄. The laser radiation takes place between the lower Stark level of ³F₄ and the higher Stark level of ³H₆. The considerable phonon broadening and high multiplicity of the Stark levels of the 4f electron provides tunability from 1.87 to 2.16 μm. We presented an analysis for the performance of side pumped quasi-three-level laser oscillators. Taking into account reabsorption loss, we present a theoretical model studies of quasi-three-level laser with particular attention given to the Tm:YAG laser. Equation for Tm:YAG quasi three-level laser system is founded, and a formula of the threshold pump power of the laser is described. The threshold pump power with different emission wavelengths versus the transmission of the output coupler is discussed, and we also analysis the influence on the threshold pump power with different emission wavelengths affected by the crystal length. With the same pump power, a lower transmission of the output coupler would result in a higher intracavity intensity. As a result, the lower laser sub-level within ³H₆ ground state manifold has higher reabsorption loss and therefore, the higher Stark sub-level within ³H₆ ground state manifold has a lower laser threshold and longer laser wavelength.

With ultrashort pulse durations and ultrahigh power densities, femtosecond laser presents unique advantages of high precision and high quality fabrication of microchannels in transparent materials. In our study, by shaping femtosecond laser pulse energy distribution in temporal or spatial domains, localized transient electrons dynamics and the subsequent processes, such as phase changes, can be controlled, leading to the dramatic increases in the capability of femtosecond laser microchannels fabrication. The temporally shaped femtosecond laser pulse trains can significantly enhance the material removal rate in both water-assisted femtosecond laser drilling and femtosecond laser irradiation followed by chemical etching. Besides, high-aspect-ratio and small-diameter microchannels are drilled by spatially shaped femtosecond laser pulses.

This paper provides an investigation of the ablation behavior of single crystal 4H-SiC and 6H-SiC wafer to improve the manufacturability and high-temperature performance of SiC using laser applications. 266nm pulsed laser micromachining of SiC was investigated. The purpose is to establish suitable laser parametric regime for the fabrication of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications. Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms, such as thermal vaporization, phase explosion, and photomechanical fragmentation, were correlated with the effects of pulse energy. The ablation threshold is obtained with ultraviolet pulsed laser ablation. The results suggested ultraviolet pulsed laser’s potential for rapid manufacturing. Excellent quality of machined features with little collateral thermal damage was obtained in the lower pulse energy range. The leading material removal mechanisms under these conditions were discussed.

The Integration Test Bed (ITB) is a large-aperture single-beam Nd:glass laser system, built to demonstrate the key technology and performance of the laser drivers. It uses two multipass slab amplifiers. There are four passes through the main amplifier and three passes through the booster amplifier. The output beam size is 360mm by 360mm, at the level of 1% of the top fluence. The designed output energy of ITB at 1053nm is 15kJ in a 5ns flat-in-time (FIT) pulse, the third harmonic conversion efficiency is higher than 70%. The first phase of the ITB has been completed in July 2013. A series of experiments demonstrated that laser performance meets or exceeds original design requirements. It has achieved maximum energies at 1053nm of 19.6kJ at 5ns and 21.5kJ at 10ns. Based on a pair of split third harmonic generation KDP crystals, the third harmonic conversion efficiency of about 70% and 3ω mean fluences as high as 8.4 J/cm² have been obtained with 5ns FIT pulse.

Combustion-driven continuous wave (CW) DF/HF chemical lasers cannot be inflamed successfully sometimes because the spark-plug-igniter is intolerant of ablation especially after long-time operation which deeply affected the reliability of the lasers. In this paper, a pre-igniter is designed as a new igniter system to produce F₂ to solve the problem. Based on the engineering practices and the principle that high-intensity spontaneous combustion will happen when mixing F₂ and H₂. The results of NF₃ and H₂ reacting with different mole ratios were calculated by CEA software. The operation reliability of the pre-igniter, the mole concentration of F₂ in the mixing gas, and the equilibrium temperature were validated by a series of experiments. The experimental results were consistent with the calculated data: with the mole ratio of NF₃ to H₂ increasing, the equilibrium temperature decreased gradually and finally leveled off; the mole concentration of F₂ in the mixing gas first increased and then decreased, achieving the maximum of about 40% when the mole ratio of NF₃ to H₂ was about 3.2. Experimental results outlined that the pre-igniter performed reliability and could produce high output of F₂. The ignition system with a pre-igniter and a spark plug could provide a new alternative for combustion-driven CW DF/HF chemical lasers.

A comprehensive design optimization of 1.55-μm high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency (IQE) while maintaing a low internal loss of the device as well. The P-doping profile and separate confinement heterostructure (SCH) layer band gap are optimized respectively with commercial software Crosslight. Analysis of lasers with different p-doping profiles shows that, although heavy doping in P-cladding layer increases the internal loss of the device, it ensures a high IQE because higher energy barrier at the SCH/P-cladding interface as a result of heavy doping helps reduce the carrier leakage from the waveguide to the InP-cladding layer. The band gap of the SCH layer are also optimized for high slope efficiency. Smaller band gap helps reduce the vertical carrier leakage from the waveguide to the P-cladding layer, but the corresponding higher carrier concentration in SCH layer will cause some radiative recombination, thus influencing the IQE. And as the injection current increases, the carrier concentration increases faster with smaller band gap, therefore, the output power saturates sooner. An optimized band gap in SCH layer of approximately 1.127eV and heavy doping up to 1e18/cm3 at the SCH/P-cladding interface are identified for our high power laser design, and we achieved a high IQE of 94% and internal loss of 2.99/cm for our design.

Broadband output from 1060nm to 1700nm and cascaded four-wave mixing generated red light pulsing is observed in a fiber amplifier set up consisting of a 5.5m double clad, double D shaped Ytterbium doped fiber, a single clad passive fiber for excess pump absorption and a splitter, both with and without a CW seed. Self-pulsing occurs from ASE due to passive Q-switching by saturable absorption effect of the active fiber and also depends on splice loss. The pulses generate broadband output by multiple four-wave mixing process with maximum broadening efficiency near 1300nm which is the zero dispersion wavelength for silica fiber. Pulses traveling both in forward and backward direction have enough peak power and energy to damage splice points and fiber components. When seeded the self-pulsing and broadband generation is often suppressed but again generate at increased pump powers.

Based on the optical path model for nonlinear imaging, we systematically investigated the propagation of flat-topped Gaussian beam which is modulated by two parallel phase-typed wirelike scatterers through computer simulation. It is found that, under certain conditions, there is no intense second-order hot image fringe in the predicated plane half-distance from the medium to the scatterer, but there are other two intense fringes whose in-beam positions are some distance deviated from those of the scatterers. These intense fringes are called second-order-hot-image-like fringes in this paper. When compared with the corresponding single scatterer case, the intensity level of the fringes is close to that of second-order hot image fringe. Besides, there are also hot images, but their intensities are much lower. The influence of the phase modulation depth of the scatterers on the propagation for both double and single scatterer cases is also investigated. First, as the phase modulation depth increases, the fringe intensity changes same as second-order hot image fringe does and their intensities keep very close to each other. Second, the fringe intensity increases at first and then decreases in a certain value range of phase modulation depth, but the hot image intensity changes inversely. Third, in the Kerr medium, the maximum intensity of the beam in the double scatterer case is higher than that in the single scatterer case except for the phase modulation value section around three rad.

Ultrasonic field in layered structure excited by a nanosecond pulsed laser irradiation is numerically simulated by finite element method. Typical calculation is executed for a configuration of a zirconium nitride (ZrN) thin film with different thickness on a steel substrate. The waveforms of surface acoustic wave are presented and the dispersion properties of surface waves in two-layered structure are analyzed by the method of phase spectral analysis, and the results show that the surface wave is anomalous dispersive with the higher frequencies propagating fast than the lower frequencies, and that with the decrease of film thickness, the dispersion of surface wave becomes more serious.

In this paper, the finite element method is used to simulate the laser generated interfacial wave on the transparent solid/solid interface in the thermoelastic region. Typical calculation is performed for the configuration of fused quartz bond to tungsten. Transient waveforms of laser-generated interfacial waves are presented. The results show that with the decrease of film thickness, the amplitude of interfacial waves becomes higher. And the surface waves all have appeared anomalous dispersion with films of different thickness. The simulations can provide theoretical guideline for the understanding of interfacial wave propagation.

In order to broaden the spectrum of laser pulse and reduce the gain narrowing effect in Nd:glass regenerative amplifier to realize the ambition of inhibiting amplitude and frequency modulation, proper quartz birefringence crystal plate is inserted into the cavity. The influence factors of central wavelength, depth of modulation and range of modulation are obtained theoretically. The width of the spectrum is broadened by controlling all the factors. Two kinds of thickness, 5mm and 6mm, are inserted into the regenerative amplifier cavity. The results of theoretical calculation and experiment both show that the effect of spectrum widening is evident, which reduces the gain narrowing effect to some extent. The amplitude and frequency modulation resulted from gain narrowing effect is inhibited when the central wavelength deflects. The simulated results show that inhibited effect of amplitude and frequency modulation is remarkable. And the method is a potential effective technique for amplitude and frequency modulation inhibition.

Aiming to the rectangle beam shape in most high power laser, the influences of the several kinds of geometrical aberrations in slit spatial filtering system have been simulated based on the diffraction theory of aberration. The aberration tolerances of all kinds of geometrical aberrations in the lenses and incident beam are obtained.

A new approach to obtain glow discharge in working mixtures of non-chain HF laser has been brought forward. The most advantage of the approach is without pre-ionization, so the contamination of pre-ionization will not happen and the laser equipment is compact and simple. It is found, if the cathode surface is equally rough, we can obtain uniform volume-discharge in SF₆ mixtures without any pre-ionization, and dispense with uniform electric field electrode profile. The form of Self-Sustained Volume Discharge (SSVD) is a Self-Initiated Volume Discharge (SIVD). We show here the possibility of obtaining SIVD with a uniform energy deposition in a system of electrodes with non-uniform electric field. Experiments show that, with rough cathode and even anode, a volume discharge is forming in non-uniform electric-field without pre-ionization in SF₆ and C₂H₆ mixtures. At the beginning of the discharge, many diffuse channels attached to bright circular cathode spots, then, diverge towards the anode, with the channels overlapping, form a spatially uniform glow discharge. SIVD has been performed at a total mixture pressure up to 8kPa and energy deposition up to 200J/l. We also report measurements of the V-I characteristics of SIVD with SF₆ and C₂H₆ mixtures at pressure up to about 8kPa. The experimental results indicate that SSVD in SF₆ and C₂H₆ mixtures develops in the form of SIVD is promising for creation of high energy and pulse-periodic HF laser.

The laser cutting of the low-carbon and stainless steel with fiber and CO₂ lasers was compared by a similar technique. The dependence of the cut surface roughness on cutting parameters was analyzed for stainless steel sheets of 3 and 5 mm and mild steel sheets of 5, 10, 16 mm. The speed at which the roughness is minimal was found. For the cutting of stainless steel with nitrogen, the minimal achieved roughness is approximately similar for two types of lasers, whereas the speed correlating with the minimal roughness was higher in the fiber-laser case. When cutting the mild steel with oxygen, the СО₂ laser enables to reach lower roughness at higher cutting speed. For the oxygen-assisted laser cutting, the empirical relations were found which connect the cutting speed and laser power associated with the minimal roughness, with the cut sheet thickness, for the cutting processes by the fiber and СО₂-laser.

Laser is widely applied in military and medicine fields because of its excellent capability. In order to effectively defend excess damage by laser, the thermal processing theory of skin tissue generated by laser should be carried out. The heating rate and thermal damage area should be studied. The mathematics model of bio-tissue heat transfer that is irradiated by laser is analyzed. And boundary conditions of bio-tissue are discussed. Three layer FEM grid model of bio-tissue is established. The temperature rising inducing by pulse laser in the tissue is modeled numerically by adopting ANSYS software. The changing trend of temperature in the tissue is imitated and studied under the conditions of different exposure dose pulse laser. The results show that temperature rising in the tissue depends on the parameters of pulse laser largely. In the same conditions, the pulse width of laser is smaller and its instant power is higher. And temperature rising effect in the tissue is very clear. On the contrary, temperature rising effect in the tissue is lower. The cooling time inducing by temperature rising effect in the tissue is longer along with pulse separation of laser is bigger. And the temperature difference is bigger in the pulse period.

While much research has been developed to achieve very large mode areas (LMA) fibers, many difficulties arise, such as bending losses, mode deformation, and high order modes suppression. The main obstacle which remains difficult to confront in LMA fibers is bending distortion. When a conventional LMA fiber is coiled, it will generally suffer large bending distortion, and the mode area will contract accordingly, which would significantly affect laser or amplifier performances for some LMA fibers. In this report, we proposed a simple and efficient way for bending compensation in LMA fiber. A periodically etching structure is proposed to compensate the deformation, bending loss, and mode-coupling effects in large mode area fibers. The numerical simulation results showed that the design not only efficiently improves the effective area, but also the fundamental mode bending loss is resistant. Without the structure, the bending losses are very low at large bending radius. When the bending radius reduces, there is a rapid increase of losses. In particular, for smaller bending radius (less than 20 cm), the fundamental mode deforms severely, and cannot normally transmit in the core. The numerical simulation results showed that the design not only efficiently improves the effective mode area, but also the fundamental mode bending loss is resistant. Even at bending radius as small as 5cm, the fundamental mode can transmit normally in the fiber with an increased mode area scaling. Furthermore, the LMA fiber with the structure can be flexibly manufactured by conventional fiber manufacturing approaches and recent etching technologies.

We have demonstrated a 1018 nm continuous wave fiber oscillator pumped by LDs operating at 976 nm. Three kinds of Ytterbium-doped dual-clad fibers, 15/130 μm fiber, 25/250 μm fiber and 30/250 μm fiber, are employed separately in the experiments. We achieve 67 W total output power with the 15/130 μm fiber for 100 W of pump power with a slope efficiency of 67%. And with the 25/250 μm fiber, 276 W total output power is generated for 372 W of pump power with a slope efficiency of 74%. In the end, 300 W output power with the slope efficiency of 81% is successfully achieved with the 30/250 μm fiber for 372 W of pump power. To the best of our knowledge, this is the highest output ever reached by a dual-clad fiber oscillator at this wavelength that ever reported in open detail.

To develop 1.55μm high power lasers with compactness, narrow spectral line-width and high wavelength stability suitable for practical applications, EY-DCFLs built in all-fiber configuration are investigated. The experimental setups are composed of Er³⁺/Yb³⁺ co-doped double-clad gain fiber, multimode 976nm pump laser diode, double-clad fiber Bragg gratings (FBGs) and (1+1)x1 side pump couplers. FBGs with different reflectivity are applied as output reflectors, and forward-pump scheme and backward-pump scheme are performed respectively. As the efficiency and the spectral stability are considered simultaneously, EY-DCFL with low reflective FBG mirror and in backward-pump manner is more desirable. In the optimized all-fiber EY-DCFL, the maximum output power with an optical-optical efficiency of more than 17% is up to 1.5 W, and the wavelength is defined at 1550.8nm with a line-width about 0.03nm.

A high-power high efficiency picosecond (ps) 355 nm ultraviolet (UV) laser was reported based on the nonlinear optical crystal of type-I phase-matching La2CaB10O19 (LCB) which possesses the characteristic of non-hygroscopicity. The high-power third harmonic generation was successfully achieved from a 1064 nm ps fundamental laser. The maximum output power of 7.81 W of 355 nm UV laser was obtained from 35.2 W 1064 nm ps laser (80 MHz repetition rate, 10 ps pulse width) with optical conversion efficiency of 22.2%. The experimental results show that the LCB crystal has a promising prospect in generating high-power high efficiency UV laser.

The coupling efficiency of the pump coupler determines the pump light injection capacity of a laser system. We have designed a pump coupler in a series connection, of which two or more pump couplers are spliced together through signal fibers to form a new pump coupler with high coupling efficiency and high output power. In the experiment, 3×1 end-pumping couplers and (2+1)×1 side-pumping couplers were made respectively and the two couplers were spliced to form a series connection. Six LDs with output power of about 200 W respectively were spliced with the six pumping arms of the new pump coupler. A total output power of this series connection pump coupler was about 1160 W, corresponding to a coupling efficiency as high as 98%. The loss of signal light was less than 0.4%.

Diode-pumped solid-state lasers are high efficiency, long lifetime, compact and reliable, so they have been covering a wide range of applications. Thermal effect is a major limiting factor in scaling the average power of high-power solid-state lasers, so it is a critical issue in designing diode-pumped solid-state lasers. The uniform pump intensity distribution in laser rod can weaken the influence of thermal effects in laser, and the research of improving the pump distribution uniformity has attracted a great deal of attention. People usually establish a model of single diode-bar pumped laser rod to calculate the distribution. However, for diode-array pumped high-power lasers, the model is limited and has deviation with the actual pump distribution, which cannot reflect the real working conditions in the laser. In this paper, the theoretical model of diode-array pumped laser rod is built. Based on the actual working environment of diode-array side-pumped Tm:YAG laser rod, the expression of pump intensity distribution in the laser medium is deduced. Additionally, the influence of total pump power, pump structure, Tm:YAG rod characteristic parameters and pump beam radius on pump intensity distribution are simulated and analyzed. Moreover, the parameters are optimized in order to obtain the optimistic results which are efficient to improve the uniformity of pump distribution. The results show that when the pumping distance from diode-array to the rod’s surface is 3mm, the distance between two rows of diode-bars is 1mm, the absorption coefficient is 330m^-1,the pump beam width is 2.5mm,the pump intensity distribution of five-way pumped laser rod is improved, and then the thermal effects could be weakened. The presented results can provide theoretical guidance to design and optimization of high-power lasers.

Large scale and broadband pulse compression grating which is used in the femtosecond Ti: sapphire laser is studied. The line density of gold coated pulse compression grating is 1740lp/mm. The working wavelength of gold coated grating is from 700nm to 900nm and its deviation angle is 16.6 degree(@800nm). By using rigorous coupled wave theory, a series of calculation results with different profiles of gold coated pulse compression grating, such as rectangular, sinusoid, semi-sinusoid, are discussed in this paper. In order to get high diffraction efficiency throughout the whole working band, the duty cycle of grating should be more than 0.5 for the rectangular or semi-sinusoidal profile of groove. Duty cycle of grating causes the diffraction efficiency to change quickly at the short wavelength. By using holographic recording method, the gold coated pulse compression gratings with the aperture of 200mm×400mm have been fabricated. The gratings exhibit -1st order diffraction efficiency in excess of 94%(TM@808nm).

We used a commercially available 75 MHz regeneratively amplified laser system emitting 50 femtosecond pulses of energies up to 3nJ at a wavelength of 800 nm. All waveguides were fabricated by focussing the femotsecond pulse train polarised parallel to the x-axis to a distance of approximately 125 μm below the sample surface using a 0.65 NA, ×40 microscope objective and translating the sample along the y axis. To find the optimum waveguide fabrication parameters the translation speed was varied from 2 to 100 μm/s. We introduces a method of measuring the refractive index of optical waveguide in ten micrometer. Useing CCD to measure the two-dimensional near-field light intensity distribution of the output cross-section of the waveguide, by measuring the two-dimensional near-field light intensity distribution of the output cross-section of the waveguide can be calculated the two-dimensional distribution of refractive index of waveguides. The context detailedly gives measurement results about femtosecond laser inducing the near-field intensity of lithium niobate optical waveguide cross-section and calculations of refractive index of optical waveguide. The results show that the refractive index of waveguides showed a large central, gradually reduce and the change of refractive index in the range of 0.001. This method is of great significance to measure the optical waveguide refractive index distribution.

The bend waveguide is one of the key components of photonic integration. In this paper, by using tightly focused femtosecond laser pulses with repetition rate of 76 MHz, pulse duration of 50 fs, average output power about 270mW, and the focus lens NA=0.65, we put forward a structure of waveguide that bent it to be 1/4 round, and research its mechanism by performing experiments. Under the above conditions, when the vertical scanning speed of the laser system is 0.8 mm / s, the width of the bend optical waveguide is about 10μm, the loss reaches a minimum value about 1dB/cm when the bend way’s radius is about 5mm. Based on the experimental results of the above parameters, we can fabricate a 1/4 round vertical bend fiber coupler, which can be applied to the connection between the chips or inter-level optical .The results showed that the bend lithium niobate waveguides can be applied in the field of optical communication and has important implications for the production of low loss, low cost and small size optical waveguide gratings , vertical fiber coupler, optical switches and other devices .

A novel pulse compression device has been developed for femto-second Ti: sapphire laser at 800nm center wavelength with 700nm~900nm bandwidth. This new kind of composite pulse compression device consists of two fused silica transmission gratings with 1250lp/mm and 3300lp/mm respectively and these two fused silica transmission gratings are located in two optical surfaces of the same fused silica plate. Owing to use anti-reflection transmission gratings with high space frequency (3300lp/mm), it can avoid the wave-front distort derived from coating antireflection film on one surface of the fused silica plate. Being made of fused silica, this new composite pulse compression device will be expected to have high laser damage threshold. The calculation results show that: the -1st order diffraction efficiency of 1250lp/mm grating is over 87% within the 700nm and 900nm broad-bandwidth for rectangular groove and TE polarization state. And the average diffraction efficiency within the 700nm and 900nm broad-bandwidth is more than 92%. At 800nm, the -1^st transmitted order diffraction efficiency is great to 96% while the transmittance of 3300lp/mm grating is up to 99.9%.

Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.

The paper presents the development of a sub-petawatt ultrashort laser facility, i.e. the upgraded super intense laser for experiment on the extremes (SILEX-I). The facility is a multi-stage Ti:sapphire chirped pulse amplification (CPA) laser system. Cross-polarized wave generation was used to improve the temporal contrast. An adaptive optical system was utilized to correct wavefront aberrations and to improve focusability before each shot. After upgrading, the maximum energy is 20.1 J, the recompressed pulse width is 26.8 fs and the peak power is up to 750 TW. The temporal contrast is around 109. The on-target focal spot size (full width at half maximum (FWHM)) is Φ6.5 μm and the focused intensity is greater than 4x1020 W/cm².

Analytical phase expressions are presented for an Offner stretcher and transmission grating compressor based on ray tracing and apply them to analyze a chirped-pulse-amplification (CPA) system. Besides, an optimization method to extract high-fidelity amplified pulse is proposed by controlling the phase of the entire system. Through theoretical analysis and numerical simulation, one can adjust the incident angle and perpendicular distance between gratings to completely compensate dispersion of Offner stretcher over entire wavelength. Finally, the optimized CPA system provides Fourier-transform-limit pulse which is identical with seed pulse.

We developed a longitudinally excited CO2 laser with a tail-free short laser pulse. In a discharge tube, two structures were researched. One is a shingle scheme that is constituted of a 45 cm-long discharge tube. Another is a tandem that is constituted of two 30 cm-long discharge tubes connected with an intermediate electrode were used. In gas media, CO₂- rich mixture (CO₂: N₂= 20: 1) was used to reduce a laser pulse tail. The laser system did not require expensive and scarce helium. A fast discharge (<1 μs) in a low gas pressure (<1.8 kPa) produced a tail-free laser pulse with the pulse width of about 100 ns. The single scheme produced an output energy of 4.7 mJ by a charging voltage of -36.3 kV, and the tandem scheme produced an output energy of 9.3 mJ by a charging voltage of -25.2 kV. The tandem scheme produced higher spike pulse by lower voltage than the single scheme. Therefore, the tandem scheme will be effective in longitudinally excited CO₂ lasers with simple and compact designs.

Stochastic Parallel Gradient Descent(SPGD) algorithm can optimize the system exhibition firsthand without using of wavefront sensor, it predigests the adaptive optic system. Based on SPGD algotithm, a model with 32 element demormable mirror was simulated, the capability of correct toward static aberration and convergence of SPGD algorithm are analysed, the relationship of gain coefficient, stochastic perturbation amplitude are discussed, an adaptive adjustment of gain coefficient is proposed, and it can improve convergence rate effectively.