This PDF file contains the front matter associated with SPIE Proceedings Volume 7062, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The considerable potential of advanced thin-film microoptics for tailoring light fields of pulsed high-power lasers even at extreme parameters like ultrashort pulse durations, broad spectral bandwidths or vacuum ultraviolet wavelengths is demonstrated. A comprehensive review of the state of the art and the most relevant aspects of this branch of modern optics is given. In particular, applications of structured dielectric, metallic and compound layers and programmable liquid-crystal devices for control and diagnostics of ultrashort pulses in space and time are discussed. Recent theoretical and experimental results of wavefront sensing, pulse diagnostics, multichannel materials processing and information encoding into the phase maps of arrayed pulsed beams of nondiffracting propagation characteristics are presented here.

Recent developments in micro-optics offer the potential of higher power and more robust ultrafast laser technology operating at high efficiency. Results using micro-optic lenslet arrays in an ultrafast, Ti:sapphire terawatt amplifier are presented. We report a final ultrafast amplified laser mode can be shaped to within 1% of the target Gaussian with a 532nm pump energy to 800nm laser pulse energy conversion efficiency of 35% in Ti:sapphire. Focusing studies demonstrate the laser system with microlens arrays can achieve a peak intensity of 10¹⁹ W/cm². Future applications of microlens arrays in 100 terawatt and possibly petawatt peak power systems will be discussed.

Dispersive elements such as prisms modify the temporal characteristics of ultrashort light pulses. In prisms the main effect that modifies the temporal characteristics of the pulse is the group velocity dispersion which can be interpreted as a result of angular dispersion of each of the electromagnetic waves of the pulse and the group velocity dispersion introduced by the glass material constituting the prisms. A model for the compression of ultrashort light pulses is presented for a set of prisms. The model shows how to obtain a good configuration in the laboratory depending on the prism material. Additionally we show that the GVD due to angular dispersion between two parallel surfaces is positive and not negative as is commonly believed. We also show that to achieve pulse compression of an input bandwidth limited pulse in a single right angle prism the reference surface should be curved and not plane as mentioned in reference ¹.

A dark hollow beam (DHB) is designed in general as a ringed shaped light beam with a null intensity center on the beam axis. DHBs have interesting physical properties such as a helical wavefront, a center vortex singularity, doughnut-shaped transverse intensity distribution, they may carry and transfer orbital and spin angular momentum, and may also exhibit a nondiffracting behavior upon propagation. Most of the known theoretical models to describe DHBs consider axially symmetric transverse intensity distributions. However, in recent years there has been an increasing interest in developing models to describe DHBs with elliptic symmetry. DHBs with elliptic symmetry can be regarded as transition beams between circular and rectangular DHBs. For example, the high-order modes emitted from resonators with neither completely rectangular nor completely circular symmetry, but in between them, cannot be described by the known HermiteGaussian or LaguerreGaussian beams. In this work, we review the current state of research on elliptic DHBs, with particular emphasis in Mathieu and Ince-Gauss beams.

We detail a method for the accurate encoding of complex wavefields in low-cost, off-the-shelf spatial light modulators capable of amplitude modulation. We assess the accuracy of our encoding scheme by producing a collection of arbitrary nondiffracting beams and evaluating their propagation characteristics when compared to those predicted by the theoretical model. The angular spectra of the beams produced using this approach is also measured and found consistent with theory.

We make use of a spatial light modulator to implement a phase-shifting interferometric method to determine the topological charge of multiple singularities embedded in the transverse phase of singular beams. This method allows us to discern between closely spaced singular points and elucidate the dynamics of optical vortices as their charge is increased continually. The transverse phase of beams with a determined phase profile are analyzed used this technique, yielding the precise location of multiple singularities as well as the value of their topological charge. We use apply this method to accurately map the phase and study the transit of vortices across fractional Bessel beams during their continuous order upconversion.

In this paper we propose and demonstrate a novel beam shaping method using vectorial vortex beam. A vectorial vortex beam is laser beam with polarization singularity in the beam cross section. This type of beams can be decomposed into two orthogonally polarized components. Each of the polarized components could have different vortex characteristics, and consequently, different intensity distribution when focused by lens. Beam shaping in the far field can be achieved by adjusting the relative weighing of these two components. As one example, we study the vectorial vortex that consists of a linearly polarized Gaussian component and a vortex component polarized orthogonally. When such a vectorial vortex beam is focus by low NA lens, the Gaussian component gives rise to a focal intensity distribution with a solid centre while the vortex component gives rise to a donut distribution with hollow dark center. The shape of the focus can be continuously varied by continuously adjusting the relative weight of the two components. Under appropriate conditions, flat top focusing can be obtained. We experimentally demonstrate the creation of such beams with a liquid crystal spatial light modulator. Flattop focus obtained by vectorial vortex beams with topological charge of +1 has been obtained.

Laser beam shapers challenge our sanity in new ways on a daily basis. From an industrial perspective; we design, analyze and then fabricate what is believed to be a simple solution to the complex problem of creating a uniform beam profile. Once the laser beam shaping optics are received and mounted, the task of alignment, fine tuning and measuring begins. At this critical juncture the most subtle changes in fabrication and design, either within a single diced wafer of elements (brothers & sisters) or from batch to batch, tend to demonstrate that small changes can greatly change the conditions or state of affairs that previously existed for alignment and performance. Once variations are detected it is up to quality assurance and manufacturing to identify these problems and figure how they came into existence. These slight variations which randomly materialize influence our ability to align and measure the true performance of laser beam shaping optical systems. Various alignment and beam shape measurement techniques are needed to ensure that the laser beam shaper is properly aligned and true performance is assessed. From an industrial perspective, it is important to rapidly understand how these variations in performance relate to the actual design, fabrication and possibly alignment errors. In many cases these variations are within the general tolerances of the fabrication process, so alignment and measurement analysis must be done to determine at what point these subtle variations exceed acceptable limits of performance. This paper will cover methods of flat top beam shaper alignment and measurement, using various tools including beam profilometry, exposure film, fluorescent media, and thermal paper and scanning sensor techniques. Analysis will be provided on specific measurement results related to fabrication errors within the beam shaping element.

Spatial laser beam profiling at focus is an essential part of quantitatively characterizing the shaped laser beam. We will discuss new methods that can profile almost any laser at almost any power level.

Near-field beam shaping optics, also called beam transformers, re-map an input Gaussian profile to a top hat profile. The top hat profile typically takes on a functional form such as a super Gaussian or a Fermi-Dirac function. The main difference between a super Gaussian and a true top hat is the presence of rounded edges. The higher the order of the super Gaussian, the sharper the profile. Sharper profiles tend to result in more diffraction effects while softer edges tend to propagate further with a uniform distribution. A balance has to be determined that may depend heavily on the application of the beam shaper with regards to performance parameters such as efficiency within the profile and the uniformity of the flat top based on the edge shape of the functional form of the top hat profile. The paper will explore different figures of merit for various functional forms that a Gaussian is typically re-mapped into and compared with that of a perfect top hat with infinitely sharp shoulders.

We will present recent advances in Kaleido Technology on the ultra-precision diamond-milling process, which is an extremely versatile tool for manufacturing of masters for wafer-based replication technologies. Diamond-milling has the advantage of being able to manufacture lenses with much larger radii of curvatures compared to etching methods. Spherical-, aspherical- and free-form-surfaces have been machined with form accuracies better than 200 nm (PV), arrays up to 50 x 50 mm have been manufactured on wafers, with lens-position accuracies better than 3 μm absolute over the entire wafer.

What defines a good flat top beam shaper? What is more important; an ideal flat top profile or ease of alignment and stability? These are the questions designers and fabricators can not easily define, since they are a function of experience. Anyone can generate a theoretical beam shaper design and model it until it is clear that on paper the design looks good and meets the general needs of the end customer. However, the method of fabrication can add a twist that is not fully understood by either party until the beam shaper is actually tested for the first time in a system and also produced in high volume. This paper provides some insight into how grayscale and binary fabrication methods can produce the same style of beam shaper, with similar beam shaping performance; however provide a result wherein each fabricated design has separate degrees of sensitivity for alignment and stability. The paper will explain the design and fabrication approach for the two units and present alignment and testing data to provide a contrast comparison. Further data will show that over twenty sets of each fabricated design there is a consistency to the sensitivity issue. An understanding of this phenomenon is essential when considering the use of beam shapers on production equipment that is dedicated to producing micron-precision features within high value microelectronic and consumer products. We will present our findings and explore potential explanations and solutions.

Near field beam shaping optics, also called beam transformers, remap an input Gaussian profile to a top-hat profile. The top-hat profile is created at some working distance away from the shaping element where a corrector element is placed to "flatten" the phase of the top-hat profile to allow it to propagate some finite distance as a "collimated" beam. Creating a top-hat profile requires the surface of the shaping element to be highly aberrated resulting in designs that are typically either a diffractive surface or an aspheric surface each composed of many higher-order aspheric coefficients. Diffractives and higher-order refractive designs offer several challenges and limitations in manufacturing. The design space of using all spherical elements or even a combination of aspheric and spherical elements has not been completely explored to see if there are any advantages of reducing the manufacturing tolerances or limitations for beam shaping systems. This paper will explore the comparison of the number of elements required for diffractive, aspheric, and spherical designs to meet the same beam shaping requirement and provide details related to the manufacturability of each type of design.

Certain high power laser applications require thin homogeneous laser lines. A possible concept to generate the necessary flat-top profile uses multi-aperture elements followed by a lens to recombine separated beamlets. Advantages of this concept are the independence from entrance intensity profile and achromaticity. However, the periodic structure and the overlapping of beamlets produce interference effects especially when highly coherent light is used. Random optical elements that diffuse only in one direction can reduce the contrast of the interference pattern. Losses due to undesired diffusion in large angles have to be minimized to maintain a good quality and high efficiency of beam shaping. We have fabricated diffusers made of fused silica for a wide range of wavelengths that diffuse only in one direction. Structures are based on an array of concave cylindrical microlenses with locally varying size and position following a well defined statistical distribution. The scattering angle can be influenced by process parameters and is typically between 1° and 60°. To predict the influence of process parameters on the optical properties, a simplified model for the fabrication process and geometrical optics have been used. Characterization of the fabricated devices was done by stylus measurements for the surface shapes, microinterferometry to measure phase profiles and high resolution goniometry to obtain far field distribution of light. The simulated data compare very well to measured optical properties. Based on our simulation tool we discuss limits of our fabrication method and optimal fabrication parameters.

Fly's eye condensers are commonly used for the beam shaping of an arbitrary input intensity distribution 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. As a consequence of the periodic structure of the regular arrays, the output intensity distribution is modulated by equidistantly located sharp intensity peaks. We propose a new concept for fly's eye condensers incorporating a stochastic tandem microlens array for the generation of an intensity far field distribution with improved homogenization under coherent illumination with the envelope of a top hat. The influences of the variance of the lens parameters and the number of illuminated lenses on the homogenization results are discussed. Measurements obtained at first prototypes fabricated by laser lithography and a subsequent UV-replication are presented.

A wide range of lasers from the UV to the IR are selected based on their optical power and spectral characteristics to match the particular absorption behavior for the material to be processed. Periodic microlens arrays are often used as multi-aperture integrators to transform the Gaussian or non-uniform beam profile into a homogenized intensity profile either in 1-D or 2-D distribution. Each microlens element samples the input inhomogeneous beam and spreads it over a given angular distribution. Incoherent beams that are either temporally or spatially incoherent can produce very uniform intensity profiles. However, coherent beams will experience interference effects in the recombination of the beams generated by each individual microlens element. For many applications, for example pulsed laser sources, it is not possible to use a rotating or moving element, such as a rotating diffuser, to circumvent the interferences resulting from the beam coherence. Micro-optical elements comprised of a randomly varying component can be used to help smooth out the interference effects within the far-field intensity profile.

Direct laser patterning of various materials is industrially implemented into several micro-system production lines such as inkjet printing, solar cell technology, flat-panel display production and medical engineering. In contrast to applications of single-mode sources, multi-mode lasers can provide very high power. This allows multi channel material processing and thus high operation speed if uniform light fields can be provided. Here within an illumination system is presented based on a high power multi-mode laser source that generates several uniform spots simultaneously without high stability requirements for the incoming laser source. These spots can be generated in various sizes and at various distances and can be located periodically and non-periodically. The concept consists of two beam processing steps: First the beam is homogenized by use of cylindrical micro-optic lens arrays. Secondly anamorphotic telecentric microoptic objectives split the beam into several uniform segments and image the spots onto the working plane. Because of LIMO's unique production technology the lens arrays can be optimized freely. It results in accurate dimensions and uniform intensity distributions for every single illuminated area. Field dimensions are only restricted by the diffraction limit. Applications could be direct material processing as well as mask illumination approaches.

High power laser sources are used in a large variety of applications for material processing, such as ablation, welding, soldering, cutting, drilling, laser annealing, micro-machining and deep-UV lithography. Using high performance optics in the laser systems to generate the appropriate beam profile becomes a key factor for getting the best results and throughput in an application field. Refractive micro-lens arrays made of glass, semiconductors or crystals provide great advantages in laser applications, by improving efficiency, precision, intensity stability and performance. With LIMO's unique production technology, free form surfaces on monolithic arrays exceeding 200 mm edge length can be manufactured with high precision and reproducibility. Each lens of the array can be designed individually and can also be shaped asymmetrically. The asymmetric shape is defined by odd- and even-polynomial terms and/or an asymmetric cut-off from a polynomial surface. Advantages of asymmetric micro-lenses are off-axis light propagation, the correction of aberration effects, or the correction of the intensity profile deformations when the illuminated surfaces are not orthogonal to the optical axis. The applications results of such micro-lens arrays are presented for beam shaping of high power diode lasers. The generation of a homogeneous light field by a 100 W laser with tilted illumination under an angle of 30°-50° is shown. A multi-kW line generator based on the superposition of over 50 diode laser bars under different illumination angles is demonstrated as well. Novel microoptical beam shapers in lithographic applications reduce the complexity of macrooptics in hyper-NA illumination systems. Extremely uniform intensity distribution can be created without using field lenses or by using simple spherical field lenses instead of complex aspheres.

Optical interference of two or more waves with different wave vectors generates a periodic, harmonic spatial profile of the optical intensity. This well known property combined with mechanical effect of light offers an excellent route to organize and manipulate large ensembles of microobjects in a controllable manner. Since the sub-micron size objects dispersed in liquid suffer from Brownian motion,such fields may assist to control its influence at will. In our experiments the periodic field is obtained by interference of co-propagating non-diffracting beams and counter-propagating non-diffracting and even evanescent fields. These types of trapping fields enable spatial organization of submicrometer-sized objects into one-dimensional arrays containing even thousands of objects, their controlled delivery over a distance of 1 mm, their sorting according to the size of refractive index. Moreover, the particle tracking enables to study the Brownian dynamics, jumps between neighboring optical traps and interactions between the objects.

Magnetorheological Finishing (MRF) techniques and tools have been developed to imprint complex, continuously varying topographical structures onto 430 x 430 millimeter optical surfaces. These optics, known as continuous phase plates (CPPs) are important for kilojoule- and megajoule-class laser systems requiring precise control of beam-shape, energy distribution and wavefront profile. MRF's sub-aperture polishing characteristics make it possible to imprint complex computer generated topographical information at spatial scale-lengths approaching 1 millimeter and surface peak-to-valleys as high as 22 micrometers to within 30 nanometers of design specifications. This paper presents the evolution of MRF imprinting technology for manufacturing large-aperture CPPs.

Internal conical refraction leads to the formation of zero (J₀) and first order (J₁) Bessel beams in superposition. The (J₀) beam retains the input circular polarisation and the (J₁) has opposite polarisation but with a single phase change around the beam axis giving it &barh; optical angular momentum per photon. This results in the conical beam having ½ &barh; net optical angular momentum per photon. This provides a simple system in which a beam of 0, ½ and &barh; optical angular momentum can be easily generated and selected with use of only a circular polariser. In the far field the characteristic Bessel beam structures are formed and can be made non-diverging with use of a lens. We report the formation of non-diverging Bessel beam of core diameter (a) of 5.7μm over a maximum non-diverging core length of 1(±.05)mm. However due to the fine structure of the conical beam at its beam waist position two cores are produces and are of opposite phase.

Beam shaping improvements of line generators based on high power diode lasers in combination with newly designed and produced high precision micro-optics lead to new applications such as hardening, metallization and annealing of different materials. Two aspects are mainly needed to be focused on for getting the best results and throughput in these applications. The first one is the overall power content along the narrow axis of the line, namely the peak intensity in combination with the beam shape. The second one is the intensity homogeneity along the long axis of the line. Herewith, a beam shaping concept that fulfils the desired requirements in a variable modality is presented. The concept consists of macro-lenses and newly designed micro-optics and results in a passively cooled high power diode laser emitting at 808nm. The laser has an output power of 1000W. The generated line has a length of 13mm and a width of <100μm at a remarkably large working distance of about 80mm. We attained an intensity distribution along the line length with a peak power density >80kW/cm² and uniformity >97%. To achieve such an extraordinary homogeneity level, several approaches based on cylindrical lens arrays were designed and tested. Methods to reduce inhomogeneities caused by diffraction effects and effects based on geometric optics are presented as well as their results. Additionally, the potential of this concept with regard to modularity, expandability and variability is reviewed. Finally, an application example - crystallisation of a thin film of a-Si on a glass substrate - is presented.

The Erbium doped fiber laser (EDFL) has demonstrated to be the ideal source for optical communications due to its operating wavelength at 1550 nm. Such wavelength matches with the low-loss region of silica optical fiber. This fact has caused that the EDFL has become very important in the telecomm industry. This is particularly important for Dense Wavelength Division Multiplexing (DWDM) which demands the use of single emission sources with different emission wavelengths. In the long run, this increases the capacity of transmission of information without the necessity to increase the infrastructure, which makes tunable laser sources an important component in DWDM applications. Many techniques for tuning have been demonstrated in the state of the art and we can mention, for example, the ones using birefringence plates, bulk gratings, polarization modified elements, fiber Bragg gratings, and very recently the use of multimode interference (MMI) effects. The MMI consists in the reproduction of single images at periodic intervals along the propagation direction of a multimode optical fiber, taking into account that these single images come from a single mode fiber optic. Here, a compact, tunable, erbium-doped fiber laser is experimentally demonstrated. The mechanism for tuning is based on the multimode interference self-imagining effect, which results in a tunable range of 12 nm and optical powers of 1mW within the region of 1549.78-1561.79nm.

There are many applications in which a laser beam with a flat-top intensity profile would be ideal, as compared to a laser beam with a non-uniform energy distribution. Standard stable optical resonators will unfortunately not generate such a laser beam as the oscillating mode. Single-mode oscillation would typically be Gaussian in profile, while multimode oscillation might deliver a beam with an averaged flat-like profile in the near field, but would diverge very quickly due to the higher order modes. In addition, if the modes are coherently coupled, then large intensity oscillations could be expected across the beam. Techniques exist to generate flat-top beams external to the cavity, but this is usually at the expense of energy, and almost always requires very precise input beam parameters. In this paper we present the design of an optical resonator that produces as the stable transverse mode a flat-top laser beam, by making use of an intra-cavity diffractive mirror. We consider the modal build-up in such a resonator and compare the mode competition between flat-top like beams, including Flattened Gaussian beams, Fermi-Dirac beams, and super-Gaussian beams. Finally, we remark on the use of an intra-cavity piezoelectric unimorph mirror for selecting a particular class of flat-top beam as the fundamental mode of the resonator.

Deformable membrane mirrors have a lot of advantages if compared with other adaptive optics devices such as bimorph mirrors, liquid crystal modulators, and thermal mirrors. Their properties are good optical power, low cost, limited power consumption, achromaticity and a good dynamic behavior. Their use in technological applications is limited by the quite low spatial resolution and maximum stroke. We propose two different configurations of push-pull membrane mirrors which improve typical performances. Both these mirrors have the advantage of having electrodes on both side of the membrane. The top side electrodes are conductive and transparent. We present a first device with a single transparent electrode on the top side and a second device with electrodes transparent pattern in the top side active region. The advantages compared to the state of the art technique for electrostatic mirror are measured and presented.

A two-element laser beam shaping system based on spherical gradient refractive index (GRIN) lenses has been designed utilizing the optical design package CODE V®. The impetus for this design is the recent development of large diameter (~ 20 mm) layered polymer spherical GRIN lenses that can be fabricated with arbitrary index of refraction profiles between 1.490 and 1.573. A merit function is developed that includes the index range constraint, radius of curvature and thickness fabrication constraints, and a mapping function which maps the Gaussian irradiance profile into a flat-top profile. The designed system features high transmission efficiency, with nearly 100% of the energy transferred to the output beam and a variance of less than 3% in uniformity from the center to the edge of the beam. The adaptability of the lens making process allows for an additional degree of freedom in beam shaping.

This paper studies the diffraction of monochromatic Gaussian beams by a sequence of parallel coaxial circular apertures in the near-field. Confocal Fresnel ellipsoids are used to design diffraction-based and wavelength-specific focusing systems through a sequence of circular apertures. The results obtained with this research show that Gaussian beams can be focused through a sequence of circular aperture diffraction effects.

The phenomena of focal shift is studied in vector Parabolic-Gauss beams. Two different criteria are employed to define the actual focus of the beam, one makes use of the energy of the beam enclosed in a circular area of radius r, oriented along the propagation axis, and the second criteria computes the second order moment of the intensity distribution with respect to the radial coordinate. The focal shift is confirmed for these type of beams, and its dependence on beam parameters such as the Gaussian-Fresnel number and their polarization is discussed.

The investigation into Bessel beams has been a topic of immense research during the past 20 years, due to the interesting properties they display. Bessel beams not only exhibit diffraction free propagation, but also reconstruction of the amplitude and phase of the beam after encountering an obstruction. Although this self reconstruction property has been previously modelled by numerous groups, the techniques involve rigorous, time-consuming computations. In this work we present an efficient method to accurately calculate the reconstruction of a Bessel beam after an arbitrary obstruction. Our method considers the well-known conical wave features of Bessel beams and looks at the projection of the obstruction in space as a result of the travelling conical waves that produce the Bessel beams.

In this paper we present the design of an optical resonator that produces as the stable transverse mode a flattened Gaussian laser beam by making use of an intra-cavity diffractive mirror. We consider the modal build-up in such a resonator and propose the required dynamic changes to an intra-cavity piezoelectric unimorph mirror for selecting the flattened Gaussian beam order of the stable mode. The feasibility of using a deformable diffractive mirror is demonstrated numerically. An optimization approach is employed to determine the optimal voltage distribution required to deform the mirror into a prescribed shape for the selection of the flattened Gaussian beam order. Good agreement between an ideal static diffractive mirror and the proposed adaptive mirror is achieved.

The second moment method of laser beam propagation allows for the calculation of the beam quality factor for any laser beam, or combination of laser beams. When several laser beams are added, their effective beam quality factor is not simply the sum of the individual beam quality factors, that is, it does not act as a linear operator. In this paper we derive an analytical expression for the beam quality factor of incoherently added laser beams whose centroids are not collinear. We illustrate the versatility of the final result by showing how this may be applied to the problem of the laser beam propagation characteristics of high power diode bar stacks.

A laboratory based technique has been devised for measuring the illumination characteristics of flashing light emitting diode (LED) sources. The difference between the photopic measurement of a continuous source and a flashing source is that some analytic method must be incorporated into the measurement to account for the response of the eye. Ohno et al have devised an analytic expression for the impulse response of the eye, which closely matches existing forms used for finding effective intensity¹. These other forms are the Blondel-Rey equation, the Form Factor method, and the Allard method.^4,5,6 Ohno's research suggests a modified Allard method, but offers no procedure for actually making the measurement. In this research, the modified Allard¹ method approach has been updated using standard laboratory equipment such as a silicon detector in conjunction with a digital multi-meter and Labview® software to make this measurement. Labview® allows exact computation of the modified Allard method. However, an approximation scheme for the conversion from radiometric units to photopic units must be adopted. The LED spectral form is approximately a Gaussian line shape with full width at half maximum of about 15 to 30nm. The Gaussian curve makes converting from radiometric to photopic units difficult. To simplify, the technique presented here estimates the spectral form of the LEDs to be a Dirac delta function situated at the peak wavelength. This allows the conversion from watts to lumens to be a simple application of the luminous efficiency curve.² For LEDs with a full width half maximum of 20nm, this scheme is found to be accurate to ± 5%.