This PDF file contains the front matter associated with SPIE Proceedings Volume 8130, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The LMJ (Laser MegaJoule) is dedicated to inertial confinement fusion. To perform this type of experiment, 160 square beams are frequency converted and focused onto a target filled with a deuterium tritium mixture. We propose to review how these beams are shaped along their propagation through the LMJ. Going upstream from the target to the laser source, specific optics has been designed to meet the beam shaping requirement. A focusing grating and a pseudorandom phase plate concentrate the energy onto the target. A deformable mirror controls and compensates the spatial phase defect occurring during the propagation through the main slab amplifiers. A liquid crystal cell shapes the beam in order to compensate the gain profile of the main amplifiers. It also protects the growth of damages that take place in the final optics of the chain. At last, a phase mirror generates a square flat top mode from a gaussian beam within a regenerative amplifier. All these optical components have one common principle: they control the phase of the spatial laser field.

Temporal contrast is an important factor affecting the application of ultraintense and ultrashort laser systems. In this paper, we employ cross-polarized wave (XPW) generation to improve the temporal contrast for ultraintense and ultrashort pulses in a 300 TW Ti:Sapphire laser facility, i.e. the super intense laser for experiment on the extremes (SILEX-I). We designed a double chirped-pulse amplification (CPA) system with an intermediate nonlinear temporal pulse filter based on XPW generation and the estimated output energy is more than 300 mJ for the new front-end system. The experimental results show that the output energy of the double CPA system is greater than 370 mJ. The amplified spontaneous emission (ASE) pedestal is suppressed significantly and the temporal contrast is improved by more than two orders of magnitude.

A variant of the Fox & Li method performing intra-cavity laser beam shaping for resonators containing an arbitrary number of amplitude and phase diffractive optics is presented. As an illustration, the problem of forcing a laser to oscillate on a single high-order transverse mode has been considered. In particular, from numerical simulation, we deduce a simple model for generating such modes with a pi-phase plate inserted into a plano-concave cavity. This model has been tested experimentally within an active cavity with a diode-pumped Nd:YVO₄ laser and an excellent agreement with numerical predictions has been found: a phase aperture located quite close to the concave mirror, and whose normalized radius κ is so that 2κ² corresponds to a zero of the desired p-order Laguerre polynomial, was sufficient to generate single cylindrical TEMp0 modes (p = 1, 2, 3) as long as its radius is correctly chosen. The laser based on the optimized features was perfectly stable, whatever the order of the generated mode.

Laser beam shaping is particularly challenging with Laser Guide Stars (LGS) and large telescopes. In Adaptive Optics (AO), LGS, elongation becomes significant with TMT (30m) and E-ELT (42m). It significantly reduces performance of Schack-Hartmann and curvature wavefront sensors. To determine the dimension of the laser source, we need to know Na layer column abundance, centroid height, Na concentration, and Na layer thickness. The LGS spot elongation is a function of the vertical sodium layer thickness and the orthogonal offset of the observer of the laser beam. R Ragazzoni (2003) (3) suggested that LGS elongation might be reduced by distribution of the laung optics around the telescope primary or secondary, all beams focusing and combining at the required elevation of 93km. Although TMT and E-ELT deal with the same parameters with respect to AL LGS, they apply them differently. For TMT (B. Ellerbroek, 2010 (4)), there will be 6 LGS wavefront sensors. Both center and side launch configurations have been considered, but the former is preferred due to cost and current progress. For E-ELT, LGS< elongation was analyszed for over a year with nocturnal as well as seasonal Na variation. The orthogonal offset is 21 m. Assuming a laser of sufficient power, a telescope could observe a low latitudes for more than 250 days per year. Six laser guide stars and three natural guide stars are forseen with launch positions at the edge of the aperture preferred. Elongation then depends on the Na density profile. Performance of TMT and E-ELT will be compared for system complexity as well as anticipated performance.

In this paper we explore vortex beams and in particular the generation of single LG_0l modes and superpositions thereof. Vortex beams carry orbital angular momentum (OAM) and this intrinsic property makes them prevalent in transferring this OAM to matter and to be used in quantum information processing. We explore an extra-cavity and intra-cavity approach in LG_0l mode generation respectively. The outputs of a Porro-prism resonator are represented by "petals" and we show that through a full modal decomposition, the "petal" fields are a superposition of two LG^0l modes.

In order to suppress the mode noise of large mode area fiber amplifier system and enhance the signal to noise ratio of the output pulse, spatial and temporal self shaping for large mode area fiber laser system are studied in this paper. For removing off the mode noise, method of beam's spacial self-shaping based on mode matching is used. By the method of mode matching, the cladding mode are removed off clearly. Then a large mode fiber amplifier with a strictly single mode is obtained. For enhancing the signal to noise ratio of the output pulse, method of beam's temoral self-shaping based on Optical Kerr effct in fiber is used. By using Optical Kerr effect, the pulse get nonlinear polarization ratation, which make pulses selfly shaped in time and the ASE pedestal is removed off clearly. As a result, by spatial and temporal self shaping, cleared pulses with a strictly single mode in spatial and cleaned pulses without ASE pedestal are obtained.

The production of an annular ring of light with a variable diameter has applications in laser material processing and machining, particle manipulation, and corneal surgery. This can readily be accomplished using a positive and negative axicon pair. However, negative axicons are very expensive and difficult to obtain with small diameters. In this paper, we present a design of an annular ring zoom system using two positive axicons. One axicon is placed a distance before a primary lens that is greater than some prescribed minimum, and the second axicon is placed after the primary lens. The position of the second axicon determines the ring diameter. The ring diameter can be zoomed from some maximum design size to a zero diameter ring (spot). Experimental results from a developmental system will be presented.

We evaluate system performance of a high-precision beam shaper using a digital micromirror device (DMD) followed by a telescope with an adjustable pinhole low-pass filter. Beam shaping quality was measured by comparing the intensity and wave-front conformity with respect to the target image, and by the energy conversion efficiency. We previously demonstrated various flattop beams with high-precision intensity and a nearly uniform wave-front by using both coherent and incoherent light sources at visible and infrared wavelengths. The diffraction efficiency analysis determined optimized operation wavelengths for different diffraction orders. This paper extends beam shaping experiments to target images of a series of 2-D sinusoidal functions. An iterative pattern refinement process, based on the point spread function (PSF) of a single DMD pixel, was used to improve the image quality and to seek the optimized DMD binary pattern. Sinusoidal-flattop profiles with different spatial carrier frequencies were chosen for the purpose of system evaluation. Experiments demonstrated RMS error ranging from 0.95% to 11.87% in the raw camera image as the sinusoidal period was decreased. The DMD-based beam shaper achieved 1% RMS error level at low system bandwidth (large sinusoid period) and maintained 5% RMS error performance for a wide bandwidth range. We analyzed the relationship between spatial intensity error and system bandwidth. The ultimate system performance had amplitude error of ±1 to ±1.5 PSFs. Iterative refinement made a significant improvement in error for low system bandwidth as compared to the simulation of a DMD pattern designed by the error diffusion algorithm.

In this paper, the generation of two-dimensional flattop focusing with second order full Poincaré beams under low numerical aperture focusing condition is proposed and experimentally demonstrated by using a liquid crystal spatial light modulator (SLM). Different input beam sizes can be accommodated by conveniently rotating the half-wave plate and adjusting the working distance. Furthermore, the quantization of the phase pattern loaded onto the SLM has been theoretically and experimentally studied, which potentially may lead to the fabrication of a compact versatile flattop beam shaper. High quality flattop profiles with steep edge roll-off can be obtained with this technique.

The performance of optical systems is typically improved by adding conventional optical components which is automatically connected to an increasing system size and weight. Hybrid optical freeform components can help to overcome this traditional tradeoff by designing a single complex optical surface that performs several optical functions at once. In this article we present the synthetic design and integrated fabrication of a reflective hybrid beam shaper offering beam deflection, transformation and splitting capabilities. The shape accuracy and surface quality of the component are demonstrated with profilometric measurements. Experimental investigations of the optical performance verify the suitability of the applied fabrication methods and design approach.

We introduce a high efficiency method to control orbital angular momentum (OAM) using a novel diffractive optical element - switchable forked polarization gratings (FPGs). We successfully fabricated the element and realized electric-optical switching of the OAM state. Unlike other approaches, this OAM manipulation requires no mechanical parts or expensive instruments. It is achieved by complex and locally periodic alignment of a nematic liquid crystal (LC) layer acting on the Pancharatnam-Berry phase. We have recently introduced fixed FPG with photo-aligned liquid crystal polymer as a highly efficient OAM state controller. We now report on our experimental implementation of electrically switchable FPGs based on liquid crystal cell. The local anisotropy is obtained by photo-alignment and liquid crystal technology. The spatial patterning is achieved by polarization holography. An applied voltage field on the cell can switch the element between an OAM generating/transforming mode and a transmissive mode. The diffraction behavior and OAM conversion behavior with respect to polarization, wavelength, and external voltage are characterized. Our current samples showed diffraction efficiency of 95% and switching time of approximately 3 ms. Because they are very efficient, thin, and easily tailored via holographic fabrication, switchable FPGs are ideal elements to implement enhanced control of OAM in high capacity information applications, among others.

Laser micromachining, drilling and marking is extensively used within the aerospace, automotive and firearms industries. The unique properties of lasers make them ideal tools for micromachining a wide diversity of materials, including steel alloys [1]. We describe the results of micromachining of low carbon steel and stainless steel alloys, using a high powered diode pumped solid state (DPSS) laser operating at a wavelength of 355nm. The laser was configured with beam conditioning optics to produce either a flat top beam or a Gaussian output which was then sent through a galvanometer scanner and telecentric lens beam delivery system. This paper outlines the interrelationship of process variables when micromachining fine features in steel and stainless steel alloys. Process variables measured included the optimum laser focus plane, energy density, galvanometer scan rate, and pulse overlap and focal spot diameter. Optimum process performance was evaluated based on a dimensional comparison of the micromachined features from each test coupon, including uniformity and surface roughness of the micromachined surface and the minimization of surface irregularities (stalagmite type slag / debris / corn row patterns) and taper angle of the micromachined feature side walls.

This paper presents an implementation of a laser beam shaping system for both heating a diamond tool and measuring the resulting temperature optically. The influence the initial laser parameters have on the resultant temperature profiles is shown experimentally and theoretically. A CO₂ laser beam was used as the source to raise the temperature of the diamond tool and the resultant temperature was measured by using the blackbody principle. We have successfully transformed a Gaussian beam profile into a flat-top beam profile by using a diffractive optical element as a phase element in conjunction with a Fourier transforming lens. In this paper, we have successfully demonstrated temperature profiles across the diamond tool surface using two laser beam profiles and two optical setups, thus allowing a study of temperature influences with and without thermal stress. The generation of such temperature profiles on the diamond tool in the laboratory is important in the study of changes that occur in diamond tools, particularly the reduced efficiency of such tools in applications where extreme heating due to friction is expected.

Safe and efficient optical alignment is a critical requirement for industrial laser systems used in a high volume manufacturing environment. Of specific interest is the development of techniques to align beam shaping optics within a beam line; having the ability to instantly verify by a qualitative means that each element is in its proper position as the beam shaper module is being aligned. There is a need to reduce these types of alignment techniques down to a level where even a newbie to optical alignment will be able to complete the task. Couple this alignment need with the fact that most laser system manufacturers ship their products worldwide and the introduction of a new set of variables including cultural and language barriers, makes this a top priority for manufacturers. Tools and methodologies for alignment of complex optical systems need to be able to cross these barriers to ensure the highest degree of up time and reduce the cost of maintenance on the production floor. Customers worldwide, who purchase production laser equipment, understand that the majority of costs to a manufacturing facility is spent on system maintenance and is typically the largest single controllable expenditure in a production plant. This desire to reduce costs is driving the trend these days towards predictive and proactive, not reactive maintenance of laser based optical beam delivery systems [10]. With proper diagnostic tools, laser system developers can develop proactive approaches to reduce system down time, safe guard operational performance and reduce premature or catastrophic optics failures. Obviously analytical data will provide quantifiable performance standards which are more precise than qualitative standards, but each have a role in determining overall optical system performance [10]. This paper will discuss the use of film and fluorescent mirror devices as diagnostic tools for beam shaper module alignment off line or in-situ. The paper will also provide an overview methodology showing how it is possible to reduce complex alignment directions into a simplified set of instructions for layman service engineers.

Advances in diamond turning technology have offered optical designers new degrees of freedom in beam shaping optics. While designers have these new manufacturing methods at their disposal, they may not be aware of special process limitations and cost drivers. The purpose of this paper is to present some of these critical manufacturing issues. We will discuss briefly special beam shaping optic types and applications. Then in more detail we will discuss the four key diamond turning techniques and the types of optics they can produce. These four key manufacturing techniques are: standard 2 axis diamond turning, slow tool servo, fast tool servo, micromilling. During the discussion we will present surface shapes, process limitations, as well as cost drivers for each technique. In summary will we present this data in a matrix that will aid the designer in selecting manufacturing techniques and optic types.

High precision femtosecond laser surgery is achieved by focusing femtosecond (fs) laser pulses in transparent tissues to create an optical breakdown leading to tissue dissection through photodisruption. For moving applications in ophthalmology from corneal or lental applications in the anterior eye to vitreal or retinal surgery in the posterior eye the applied pulse energy needs to be minimized in order to avoid harm to the retina. However, the aberrations of the anterior eye elements cause a distortion of the wave front and consequently an increase in size of the irradiated area and a decrease in photon density in the focal volume. Therefore, higher pulse energy is required to still surpass the threshold irradiance. In this work, aberrations in an eye model consisting of a plano-convex lens for focusing and 2-hydroxyethylmethacrylate (HEMA) in a water cuvette as eye tissue were corrected with a deformable mirror in combination with a Hartmann-Shack-sensor. The influence of an adaptive optics aberration correction on the pulse energy required for photodisruption was investigated. A reduction of the threshold energy was shown in the aberration-corrected case and the spatial confinement raised the irradiance at constant pulse energy. As less energy is required for photodisruption when correcting for wave front aberrations the potential risk of peripheral damage is reduced, especially for the retina during laser surgery in the posterior eye segment. This offers new possibilities for high precision fs-laser surgery in the treatment of several vitreal and retinal pathologies.

This paper documents the design, analysis and testing of Micro Lens Array (MLA) beam integrator systems for the investigation of the injection of a single mode laser into square and round fibers (two sizes each), and a rectangular fiber. This research focused on methods that could enhance the development of a uniform speckle pattern at the output end of the fiber, the injection systems are designed to fill the modes of the fiber (as much as practicable) and match the NA of the fiber. The designs for the square and rectangular fibers are based on lenslet array components available from off-the-shelf fabricators. It can be argued that the number of modes injected into the fiber is proportional to the number of lenslets in the input beam. Evaluation at the design phase leaned towards lenslet arrays with small lenslet sizes. However, diffraction limits how small the lenslet arrays can be. For this reason the final designs were configured using a micro lens array (MLA) based imaging integrator approach. An overview and tests results will be presented to evaluate the benefits and limitations of such fiber injection techniques.

Multi focus optics are used for parallelizing production and for large-scale material processing. These elements split the beam into a periodic spot pattern with a defined grid and spot size. The challenge lies in the generation of a homogeneous envelope. Additionally the demand for flexible systems for an in-process changing of optical properties increases. Different components for multi spot generation like diffractive optical elements or micro lens arrays have been investigated. Diffractive optical elements offer large degree of freedom in the generation of arbitrary intensity distributions. In the paper we demonstrate the use of a diffractive element in combination with a multi spot generator. Within the paper we present the investigation of a micro lens array in a fly's eye condenser setup for the generation of homogeneous spot patterns. The multi spot generator is combined with a galvanometer scanner for forming an arbitrary shaped laser beam into a spot-, ring or arbitrary array pattern. We show the principal functionality of the multi-spot generator. Furthermore constrains of this setup are demonstrated. The multi spot scanner is used for micro structuring of silicon with a nanosecond diode pumped solid state laser. The ablation rate and structure quality are compared to single spot processing.

Many applications of lasers seek nowadays for focal spots whose corresponding volume is getting smaller and smaller in order to ensure high spatial resolution. This problem, studied by many research groups around the world, is the core of this research work which deals with controlling the focal volume of a focused laser beam. Indeed, our objective is to develop a new method based on spatial treatment of laser beams, allowing to solve, in an original and efficient manner, two fundamental issues that have not been treated satisfactorily yet, i.e. : (i) The generation of a special laser beam, which has the ability to produce a focal volume smaller than the one resulting from a more common Gaussian beam, when focused by an ordinary lens. The expected reduction factor of the focal volume is in the order of several hundreds, when the existing methods do not exceed few tenths. (ii) The decoupling between transversal and longitudinal resolutions within the focal volume, contrary to Gaussian beams whose depth of field is proportional to the square of its beam-waist radius. The method that it is developed is based on two steps: First, the laser is forced to oscillate on a high-order but single transversal mode TEMp0, which is secondly spatially beam-shaped thanks a proper Diffractive Optical Element (DOE) that allocates the super-resolution feature².

In this paper, we present a novel technique for beam shaping and mode conversion of elliptical laser beams employing vortex phase elements. We show that a vortex phase element with topological charge m=1 can effectively switch between elliptically shaped fundamental TEM₀₀ mode and TEM₀₁ mode. When used with a spatial light modulator, the proposed technique allows beam shape adjustments by applying electrical control signals. Compared to existing static mode conversion techniques, the presented technique may perform dynamic switching between the different laser modes. The developed technique may have several practical applications in the fields of photonics and laser optics, including beam splitters and interferometers, fiber lasers, high speed optical modulators, and optical tweezers.

In this paper, we discuss the properties of propagation-invariant structured laser beams. We show the influence of different beam obstructions on the resulting structure of the beams. We present a reconstruction technique that, in spite of the remarkable self-healing properties of the propagation-invariant beams, allows us to define the size and shape of the obstructions encountered by the structured beam during propagation. The presented technique may have several practical applications in the fields of photonics and laser optics, including high resolution microscopy, optical information processing, and optical cryptography.

In this paper, a pulse stretcher based on multilayer volume holographic gratings(MVHG) is shown. The diffraction properties of the pulse stretcher under ultrashort pulse are investigated based on the modified multilayer coupled wave theory. The spectral intensity distributions of the diffracted beam are calculated. The diffraction bandwidth, pulse duration, pulse expansion and the total diffraction efficiency of the pulse stretcher are also analyzed. The pulse broadening is accomplished by adjusting the width of the intermediate layer of a system of MVHG. The calculation results show that using this new pulse stretcher system to broaden pulse has many advantages: the efficiency of diffraction is high, the structure of stretcher is adjustable to vary the amount of temporal broadening of the light pulse, and the structure is also more compact than alternative approaches.

An efficient technique of utilizing Dammann grating and phase plate to get high power and high brightness laser beam from phase-locked laser array is presented. The conjugate Dammann grating and the phase plate are placed in the back and front focal plane of a Fourier lens respectively. In order to improve the beam combining efficiency, Continuous grating of high diffraction efficiency is used to replace the Dammann grating. Analysis shows that the Continuous grating which has a higher diffraction of efficiency is also suitable for beam combining of the presented system.

Volume holographic gratings (VHG) are of wide interest in many applications because of their properties of high diffraction efficiency, excellent wavelength selectivity and angular selectivity. Recently, because of more free parameters, multi-layer volume holographic gratings (MVHG) have become an ideal candidate for various promising technological applications such as optical interconnects, pulse shaping and optical filters. Therefore, some knowledge of the diffraction behaviors of such system would be very valuable for characterizing and optimizing such volume diffractive optical elements. In this paper, we extend the coupled wave theory of multi-layer gratings to study the Bragg diffraction properties of continuous wave, ultrashort laser pulse and chirped ultrashort pulse, and present a systematically theoretical analysis on the spectrum distribution of the diffracted intensities, the diffraction bandwidth of a system of MRVHG. The system of MRVHG is composed of multiple layers of reflection VHG separated by intermediate layers. The comparisons of the diffraction characteristics for these beams are investigated.

This study used the aspheric lens to realize the laser flat-top optimization, and applied the genetic algorithm (GA) to find the optimal results. Using the characteristics of aspheric lens to obtain the optimized high quality Nd: YAG 355 waveband laser flat-top optical system, this study employed the Light tools LDS (least damped square) and the GA of artificial intelligence optimization method to determine the optimal aspheric coefficient and obtain the optimal solution. This study applied the aspheric lens with GA for the flattening of laser beams using two aspheric lenses in the aspheric surface optical system to complete 80% spot narrowing under standard deviation of 0.6142.

We demonstrated that optical vortices can be created by means of interference of three waves from a common laser source. Different intensity patterns can be generated starting from common two wave interference fringes up to regular hexagonal structures. The created vortices exist throughout the transition from two wave to complete three wave interference and have been shown to move along predictable lines in space under perturbations of contrast of waves. The law of conservation of topological charge was fulfilled for the interference of three waves.

We introduce and discuss the shaping properties of a novel optical lattice that we call dynamic parabolic optical lattice (DPOL). While the transverse structure of the DPOL is characterized by a suitable superposition of parabolic nondiffracting beams with different transverse wave numbers, its longitudinal structure exhibits a controlled periodic modulation. We address the existence and the controlled stability of two-dimensional solitons in DPOLs and characterize its propagation. An efficient numerical method for constructing nondiffracting parabolic beams and DPOLs is presented as well.