This PDF file contains the front matter associated with SPIE Proceedings Volume 6663, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Many applications in laser manufacturing like semiconductor lithography, micro-machining, micro-structuring or material-analysis require a homogeneous intensity distribution of the laser beam over its complete profile. Refractive and diffractive beam homogenizer solutions have been developed for this challenge, but their applicability strongly depends on the physics of the individual laser beam. This paper investigates the influence of laser beam properties like spatial coherence for microlens beam homogenizers. Diffraction at the small lens apertures and interference effects of periodic arrays are explained by using diffraction theory. Different microlens beam homogenizer configurations are presented. Design considerations that might be helpful for the layout of a specific microlens beam homogenizer system are discussed. It is shown that, among other factors, the Fresnel number is the most important quantity to characterize the influence of diffraction effects on microlens laser beam homogenizers. The influence of the spatial partial coherence will be explained for the example of a Fly's eye condenser. For cw laser sources, the influence of a rotating diffuser plate on grating interference and speckles effects is investigated. Finally, the theory will be compared to some practical examples in planar laser measurement techniques, in combustion diagnostics and micromachining with Excimer lasers.

We investigate the phase conjugating element of a two element Fourier transform beam shaping scheme and the impact this element has on the resulting propagation. We show that there are stricter limitations placed on the system when using such a phase correcting element, and that even at 10× the previous limits one can observe intensity errors due to inaccurate phase conjugation.

The refractive, aspheric beam shaper in its Keplerian configuration has a focus between the two lenses and near that focal point are caustic surfaces on which the optical intensity, in the geometrical optics approximation, is infinite. We use the intensity law of geometrical optics to find the caustic surfaces and the irradiance everywhere in the caustic region. The theoretical results are in good agreement with measurements on an aspheric beam shaping lens using a CCD camera.

A simple model of a Porro prism laser resonator has been found to correctly predict the formation of the "petal" mode patterns typical of these resonators. A geometrical analysis of the petals suggests that these petals are the lowest-order modes of this type of resonator. Further use of the model reveals the formation of more complex beam patterns, and the nature of these patterns is investigated. Also, the output of stable and unstable resonator modes is presented.

A beam shaping method based on the superposition and unwinding of vortex beams is proposed. This method allows for the continuous tuning of the orbital angular momentum content and longitudinal intensity distribution of the beam. We provide with a closed expression for the orbital angular momentum content of a general superposition of vortex beams and find its relation to the functional parameters of the beams. We compare our theoretical predictions with experimental results with excellent fidelity.

We investigate theoretically and experimentally the propagation characteristics of the Helical Hermite-Gauss beams corresponding to the helical Ince-Gauss beams in the limit of infinite ellipticity. Particular attention is paid to the transverse irradiance structure, the orbital angular momentum density, and the vortex distribution.

State-of-the art laser material processing systems impose strong requirements on the achieved beam quality. Often a homogeneous intensity distribution in one or two directions with peak-to-valley ratio <1% is required. In this case diffraction and interference effects must be treated with highest accuracy. To take this into account we have developed our own software for optical design and simulation based on the solving of wave equations. This gives us a new approach to beam shaping and beam steering problems. Special attention to wave effects has to be paid particularly when the laser beam profile has to be transformed to a flat-top, when forming a highly homogeneous light line with large depth of focus or when performing high resolution electro optical beam deflection. Using the wave properties of light raises special demands on the micro lenslet arrays, because the phase relations of the individual beamlets become important. LIMO's unique technology for manufacturing and quality control of the micro lenses with a free programmable surface shape provides successful solutions for these tasks. Beam shaping schemes designed by us involve high technology applications such as micro-lithography and laser annealing. High beam performance is achieved using numerous properties of various light sources: the low spatial coherency of excimer lasers, partially coherent multi mode solid state lasers and semiconductor lasers, highly coherent (single mode) gas lasers, solid state lasers and semiconductor lasers.

Lens array arrangements are commonly used for the beam shaping of almost arbitrary input intensity distributions into a top-hat. The setup usually consists of a Fourier lens and two identical regular microlens arrays - often referred to as tandem lens array - where the second one is placed in the focal plane of the first microlenses. Due to the periodic structure of regular arrays the output intensity distribution is modulated by equidistant sharp intensity peaks which are disturbing the homogeneity. The equidistantly located intensity peaks can be suppressed when using a chirped and therefore non-periodic microlens array. A far field speckle pattern with more densely and irregularly located intensity peaks results leading to an improved homogeneity of the intensity distribution. In contrast to stochastic arrays, chirped arrays consist of individually shaped lenses defined by a parametric description of the cells optical function which can be derived completely from analytical functions. This gives the opportunity to build up tandem array setups enabling to achieve far field intensity distribution with an envelope of a top-hat. We propose a new concept for fly's eye condensers incorporating a chirped tandem microlens array for the generation of a top-hat far field intensity distribution with improved homogenization under coherent illumination. The setup is compliant to reflow of photoresist as fabrication technique since plane substrates accommodating the arrays are used. Considerations for the design of the chirped microlens arrays, design rules, wave optical simulations and measurements of the far field intensity distributions are presented.

Imaging based beam delivery systems are used for precision laser material processing applications such as microvia drilling, wafer dicing/scribing and micro-machining. A critical element within the beam delivery system is the aperture or mask which is employed to form the desired spot or image on the surface of the material to be laser processed. Laser beams for precision laser processing are shaped into uniform beam profiles, so the aperture is illuminated with a plane wave and subsequently imaged with a projection lens, forming a flat top spot on the target material. Apertures, in conjunction with illumination by diffractive optical beam shapers can produce ringing or noise at the image plane, causing undesirable effects to the features being formed into the material being processed. These effects become even more severe as the diameter of the aperture decreases (Diffraction effects increase) and/or when the de-magnification is increased (Long path lengths). Since the apertures follow the general principle of diffraction of a circular aperture it is possible to model these effects optically. However, beam shapers have unique attributes that can not be adequately realized in an optical ray tracing model. This paper investigated the use of digital apertures as an alternative to hard apertures to improve the uniformity of the imaged spot, with an emphasis on better uniformity.

Diffractive beam shaping, using a remapping approach, requires a laser source that is well characterized and stable. Recent advances in the development of fiber lasers have shown stable, high quality, TEM00 single mode performance at powers < 200 Watts for 1090 nm. This paper will give a detailed account of the design and experimental results for a 5.5 mm 1/e2 fiber lasers shaped by an off-axis diffractive beam shaper to produce tophat focused spots < 50 microns. One application of interest is in the area of micro welding of thin stainless steel sheets. Experimental data will be presented for this micro welding application.

Systems for the reshaping of laser beams are widely used today. Most applications can be found in the fields of technical illuminations or material processing. Beam shaping is typically done using one or more diffractive or refractive surfaces. The fabrication of these surfaces is quite expensive in the most cases, especially if merely prototypes or a small number of systems are required. The authors will show ideas how to design beam shaping systems for the reshaping of circular Gaussian beams into circular Top Hats using standard spherical catalog lenses. These ideas allow the development of low cost beam shaping systems. The required elements can be ordered for less than $100 in catalogs typically. Concepts for the selection of lenses from catalogs as well as optimization strategies will be explained. Theoretical design examples will be discussed and simulation results will be compared with measurement data.

High power laser sources are used in a large variety of applications for materials processing. The most common are welding, soldering, cutting, drilling, laser annealing, micro-machining, ablation and micro-lithography. Beside the right choice of the suitable laser source adequate high performance optics for the generation of the appropriate beam profile are essential. Widely used geometries are square, rectangular light fields or light lines with homogeneous intensity distributions. The whole devolution from optical design and engineering to products and applications is demonstrated. LIMO has developed powerful software tools founded on Maxwell's Equations taking into account all important physical aspects of the beam shaping task. Various beam shaping principles, e.g. phase shifting for single-mode lasers, beam mixing for multi-mode lasers and other beam transformation schemes are discussed. Based on LIMO's unique production technology with computer-aided design free-form micro-lens surfaces can be structured cost-effectively on wafer-basis. Thus, the theoretically optimized surfaces can be transformed with high precision into a large range of materials. Typical products, their beam profiles and the respective application results are exemplarily shown for optical micro-lithography, micro-machining with Nd:YAG lasers and their harmonics as well as a-Si thin film annealing for flat panel display production.

Polytetrafluoroethylene (PTFE) is an ideal material for use in industrial, automotive and consumer electronics. Specifically, PTFE has outstanding physical properties; such as chemical inertness and resistance to chemical corrosion, even when exposed to a strong acid, alkali and oxidants. Its properties provide for superior electrical insulation and thermal stability, which is not affected by wide ranges in temperature and frequency. Its non-absorption of moisture makes it a perfect material for consideration in micro optical, retro-reflector or diffuser type devices used in handheld displays, flat panel displays as well as automotive, industrial and home lighting. This paper presents an overview of a unique fabrication method that incorporates a variety of elements to establish a processing technique that can form micro diffractive, holographic and reflective structures into PTFE materials. By means of modifying an existing known molding process, this new technique incorporates the addition of a vacuum to assist in the reliable molding and densification of the PTFE as well the use of a micro-structured electroformed shim to form small microstructures into the surface of the PTFE material. The combination of the vacuum and the electroformed shim within the molding process noticeably increases the precision, reproducibility and resolution of micro-structures that can be realized. The paper will describe the molding hardware involved, process parameters and the resulting structures formed. Optical function testing and metrology of the micro-structure geometry formed on each sample will be compared to the original design mandrel geometry [1].

It is commonly known that a diffractive optic can be designed to split an incoming beam into many spots or orders to produce various shapes and patterns. A desire to produce an equilateral triangle in the far-field for applications such as ophthalmology surgery, topographical LIDAR mapping, and in material processing is an interesting case where there are multiple design choices. In this paper, we will present grayscale and binary approaches of a corner cube array and hexagonal phase plate that produce an equilateral triangle in the far-field with equal amount of energy in each of the three spots. An efficiency analysis will be presented showing various results obtained using scalar wave theory versus a rigorous coupled wave analysis.

A new class of optically generated holographic projection masks is reported that shapes a high power laser beam into any number of image forming sub-beams. Unlike computer generated holograms or TIR volume holography approaches, the work reported here involves a phase only transmission in-line optical hologram to shape beams and image patterns on a workpiece. By combining the functions of beam homogenizer, mask and projection lens into a single in-line optical element, this approach yields a highly efficient but greatly simplified lithography system for ablation patterning. A lower cost ablation process tool with throughput 10-100 times that of existing tools is one result. This report examines the use of high power holographic projection masks to replace traditional reflective photomasks and the associated projection imaging optics currently used in laser ablation systems. A holographic projection mask also exhibits image redundancy, reducing the need for beam homogenization and increasing its resistance to print defects produced by contamination or damage.

A heated horizontal spinning pipe causes gases inside it to assume dynamics resulting in a graded index lens - a spinning pipe gas lens (SPGL). A CFD model is presented which shows that gas exchanges of the SPGL with the surroundings resulting in a near parabolic density distribution inside the pipe created by the combination of velocity and thermal boundary layers. Fluid dynamic instabilities near the wall of the pipe are thought to have an deleterious effect on the quality of the beam and its wavefront. Measurements of the wavefront of a propagating laser beam shows strong defocus and tilt as well as higher order aberrations, thereby reducing the beam quality factor (M²) of the output beam. Results are presented as a function of pipe wall temperature and pipe rotation speed.

There are different ways to design and build beam shapers; generally, it is based on diffractive or refractive optical elements. Both solutions have different kinds of advantages and disadvantages. Diffractive designs are very sensitive to parameters like wavelength, nevertheless, they are in general easier to manufacture. The refractive design offers more flexibility in terms of wavelength. In general, there are two possibilities for manufacturing such refractive beam shapers, either on basis of spheres or on basis of aspheres. Concerning the production of aspheres there have always been strong limitations either in terms of the surface form - only a small deviation from best fit sphere/plano surface is possible - and/or in terms of surface accuracy. As fully discussed in literature it is necessary to increase form accuracy in case of using aspherical forms with small aspherical departures. In other words, the quality of the beam shaper does not necessarily improve by using aspherical forms with small aspherical departures. On the contrary, one has to increase the form accuracy of the beam shaper element in order to keep beam quality standards. Based on ten years of experience a technology has been developed that allows us manufacturing of optical surfaces in almost all kinds of forms, shapes and sizes. By now it is possible to produce aspherical forms both concave and convex, with strong departures from the best fit sphere as well as with inflection points from 4 to 200 mm in diameter. By now it is possible to manufacture aspherical surfaces with big departures while securing high accuracies. It is the purpose of this paper to give an understanding of how the refractive approach can be applied for the fabrication of aspherical beam shapers.

Laser scribing technology was introduced in LED wafer singulation four years ago and has been gaining significant success. But as GaN/Sapphire wafers keep shrinking the LED chip size (8mil) yet continue to remain on a 2" wafer size, laser process engineers face heavy pressure from the LED industry to further increase throughput. Since raising laser power degrades the performance of GaN, a process engineer can't just substitute a higher power laser and expect quicker throughput. Even if the scribing speed can be increased with a higher powered laser, the efficiency on throughput won't be significant because of the small wafer size and enormous amount of dicing streets. In order to efficiently utilize a more powerful laser, beam splitting optic need to be employed to scribe the wafer with simultaneous multiple beams. During production we used a triple beam design and found that even scribing at one-third the speed, we can get more than 30% increase in throughput. How this technique adapts into this application will be presented in this paper, as well as the challenges encountered under a real production environment.

Beam shaping has the potential to provide comfort to people who require or seek laser based cosmetic skin procedures. Of immediate interest is the procedure of aesthetic hair removal. Hair removal is performed using a variety of wavelengths from 480 to 1200 nm by means of filtered Xenon flash lamps (pulsed light) or 810 nm diode lasers. These wavelengths are considered the most efficient means available for hair removal applications, but current systems use simple reflector designs and plane filter windows to direct the light to the surface being exposed. Laser hair removal is achieved when these wavelengths at sufficient energy levels are applied to the epidermis. The laser energy is absorbed by the melanin (pigment) in the hair and hair follicle which in turn is transformed into heat. This heat creates the coagulation process, which causes the removal of the hair and prevents growth of new hair [1]. This paper outlines a technique of beam shaping that can be applied to a non-contact based hair removal system. Several features of the beam shaping technique including beam uniformity and heat dispersion across its operational treatment area will be analyzed. A beam shaper design and its fundamental testing will be discussed in detail.

Laser dicing of wafers is of keen interest to the semiconductor and LED industry. Devices such as ASICs, Ultra-thin Wafer Scale Packages and LEDS are unique in that they typically are formed from various materials in a multilayered structure. Many of these layers include active device materials, passivation coatings, conductors and dielectric films all deposited on top of a bulk wafer substrate and all potentially having differing ablation thresholds. These composite multi-layered structures require high finesse laser processes to ensure yields, cut quality and low process cost. Such processes have become very complex over the years as new devices have become miniaturized, requiring smaller kerf sizes. Of critical concern is the need to minimize substrate micro-cracking or lift off of upper layers along the dicing streets which directly corresponds to bulk device strength and device operational integrity over its projected lifetime. Laser processes involving the sequential use of single or multiple diode pumped solid state (DPSS) lasers, such as UV DPSS (355nn, 266nm, 532 nm), VIS DPSS (~532 nm) and IR DPSS (1064nm, 1070nm) as well as (UV, VIS, NIR, FIR and Eye Safe Wavelengths) DPFL (Diode Pumped Fiber Lasers) lasers to penetrate various and differing material layers and substrates including Silicon Carbide (SiC), Silicon, GaAs and Sapphire. Development of beam shaping optics with the purpose of permitting two or more differing energy densities within a single focused or imaged beam spot would provide opportunities for pre-processing or pre-scribing of thinner cover layers, while following through with a higher energy density segment to cut through the bulk base substrates. This paper will describe the development of beam shaping optical elements with unique beam shapes that could benefit dicing and patterning of delicate thin film coatings. Various designs will be described, with processing examples using LED wafer materials.

In recent years, demanding adaptive optics applications have driven advancements in microelectromechanical systems (MEMS) deformable mirrors. The latest developments in adaptive optics for extremely large telescopes and other astronomical applications calling for thousands of control points have pushed high actuator mirror arrays. The need to compensate for large amplitude, high order wavefront aberrations in retinal imaging have pushed for high stroke, high spatial resolution deformable mirrors. Aerospace and military defense applications with long operational life times have created demands for rugged, highly reliable micromachined devices. Finally, the impending commercialization of deformable mirrors for bioimaging applications has created a requirement for a low-cost adaptive optics solution. The variety of applications with their respective requirements has resulted in versatile MEMS devices for advanced optical control and thus well-suited for many laser beam shaping applications. This paper will describe the design, manufacturing, and testing results of the latest generation of optical quality micromachined deformable mirrors. Recent testing of a 4096 actuator deformable mirror and a newly released a 140 actuator, six micron stroke mirror will be demonstrated. A high-speed electronics driver for a 1024 actuator deformable mirror designed for laser beam shaping in optical communication will also be demonstrated. This paper will show how the applications of micromachined deformable mirrors can be extended to laser beam shaping for industrial machining, laser communication, and femto-second pulse applications.

The use of diffuse reflectance materials in laser pump reflector design can lead to significant improvements in laser performance over reflectors employing more traditional, specular (or mirror-like) reflectors. Diffuse reflectors provide a more predictable and uniform beam profile, and reduced susceptibility to parasitic oscillations. Since laser pumping involves multiple reflections within the pump chamber, the efficiency of a laser pump chamber can be significantly affected by relatively small changes in reflectance. For example, a chamber with a reflectance factor of approximately 99% over the 400 to 1000 nm range, can provide a 15% gain in performance over a comparable 98% reflective chamber, even though the reflectance factor is only 1-2% lower. Much larger gains are possible over typical ceramic reflectors. This paper will examine high performance PTFE as a reflector in laser pump chambers compared to other materials. Gains in performance through reflectance and diffuseness are shown through mathematical models, experimental results and real world case studies.

We consider two technically important problems related to implementing a new acousto-optical spectrometer for the analysis of radio-astronomical signals. This project lies in a line with the program of developing the metrological equipment for the Mexican Large Millimeter Telescope. Here, the main attention is paid to arranging the optical scheme of such a spectrometer, namely, to designing the prism-made optical beam shaper and to characterizing the potential resolution, i.e. the number of resolvable spots, inherent in acousto-optical spectrometer exploiting a one-phonon optimized anomalous light scattering by acoustic phonons in a large-aperture cell made of the specifically oriented tellurium dioxide single crystal.

A resonator to generate a single LG_p=0^{[mathematical symbol 'ell'] =1} donut mode with high mode purity up to 99% is reported. The resonator consists of three lens elements and one binary phase element. With such high mode purity, the generated donut laser beam is applicable to a number of studies including trapping and rotating micro particles, non-linear optics, and atomlight interaction. The tolerance of the proposed configuration is discussed, as well methods of compensating for the thermal effects of laser materials while manipulating the resonator in a practical laser diode end-pumped solid state laser system.

Recent approaches to demonstrating adaptive optics and atmospheric turbulence have made use of spatial light modulators (SLMs) as the active phase element. However, there are limitations in using SLMs as an accurate method of simulating turbulence phase screens. In this work we investigate the limitation of laser beam shaping with a phase-only spatial light modulator for the simulation of dynamic and pseudo-random turbulence in the laboratory. We find that there are regimes where there are not sufficient pixels to resolve the phase. At the higher end of this range, at strong turbulence levels, the zonal regions are tightly packed. This leads to two simultaneous effects: a phase screen with low efficiency in some regions, and a modified turbulence structure due to the shifting of the zone peaks. These amplitude and phase distortions have a deleterious effect on the accurate simulation of the turbulence. At the lower end of the range, at weak turbulence, the phase change is too small to describe with sufficient grey scale levels, since the full 256 levels are associated with a full 2π phase shift. Further limitations include the frame rate of SLM for time-evolving turbulence. We show experimental results demonstrating these limitations, and discuss the impact this has on simulating turbulence with SLMs.

Helmholtz-Gauss beams can be expressed as a superposition of tilted Gaussian waves, and combining this spectrum with perturbation theory using the Rytov approximation can be useful in order to study the propagation of Helmholtz-Gauss beams through random media. We do this by obtaining the second-order statistical properties of the fields. We compare our results with previously reported calculations for pure Gaussian beams and nondiffracting beams. Our analysis is restricted to the weak regime of atmospheric fluctuations.

We study the propagation properties of X-shaped localized higher-order Mathieu pulses. Several spectral functions in the optical domain are proposed and discussed using physical examples. We derive the relevant expressions using a formalism based on the angular spectrum of plane waves.