This PDF file contains the front matter associated with SPIE Proceedings Volume 7789, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Over the last thirty five years there have been many papers presented at numerous conferences and published within a host of optical journals. What is presented in many cases is either too exotic or technically challenging in practical application terms and it could be said both are testaments to the imagination of engineers and researchers. For many brute force laser processing applications such as paint stripping, large area ablation or general skiving of flex circuits, the opportunity to use a beam shaper that is inexpensive is a welcomed tool. Shaping the laser beam for less demanding applications, provides for a more uniform removal rate and increases the overall quality of the part being processed. It is a well known fact customers like their parts to look good. Many times, complex optical beam shaping techniques are considered because no one is aware of the historical solutions that have been lost to the ages. These complex solutions can range in price from $10,000 to $60,000 and require many months to design and fabricate. This paper will provide an overview of various beam shaping techniques that are both elegant and simple in concept and design. Optical techniques using axicons, prisms and reflective integrators will be discussed in an overview format.

The statistical distributions of phase values in computer-generated holograms produced with iterative algorithms are studied. Useful relationships between the parameter values applied in the iterative technique used for their generation and measured performance are provided.

This paper presents a beam shaping device namely, a Diffractive Optical Element (DOE), which is used to change a beam having a Gaussian intensity profile into a beam with a uniform intensity profile. The DOE used in this work was fabricated from ZnSe and its performance was evaluated using a cw CO₂ laser. In most cases such elements are effective only at a specific design wavelength. However, in this paper we report on the design conditions which allow for wavelength independent elements. It was found that the DOE was able to successfully transform a Gaussian beam into a flattop beam for four different wavelengths in the range 9.2 μm to 10.6 μm. We also present experimental results on misalignment effects and it was found that small radial offsets of the incident beam on the DOE had a significant disruptive effect on the flattop beam profile.

A numerical and experimental comparison between different synthetic holographic codes is presented. Its performance is evaluated considering the generation of Bessel and Laguerre-Gaussian beams, as examples. Some reviews of computer generated holograms (CGHs) have been published in the literature but none of them have included a detailed comparison of their performance in the encoding of structured optical fields. The numerical evaluation includes an analysis of the theoretical features of each hologram and a calculation of Signal-to-Noise Ratio of the reconstructed field while the experimental evaluation assume the implementation of the holograms using a pixelated phase modulator.

Increasingly stringent requirements on the performance of diffractive optical elements (DOEs) used in wafer scanner illumination systems are driving continuous improvements in their associated manufacturing processes. Specifically, these processes are designed to improve the output pattern uniformity of off-axis illumination systems to minimize degradation in the ultimate imaging performance of a lithographic tool. In this paper, we discuss performance improvements in both photolithographic patterning and RIE etching of fused silica diffractive optical structures. In summary, optimized photolithographic processes were developed to increase critical dimension uniformity and featuresize linearity across the substrate. The photoresist film thickness was also optimized for integration with an improved etch process. This etch process was itself optimized for pattern transfer fidelity, sidewall profile (wall angle, trench bottom flatness), and across-wafer etch depth uniformity. Improvements observed with these processes on idealized test structures (for ease of analysis) led to their implementation in product flows, with comparable increases in performance and yield on customer designs.

Refractive beam shapers of the field mapping type find use in various industrial, scientific and medical applications, where generation of a collimated beam of uniform intensity is required. Due to their unique features, such as: low output divergence, high transmittance and flatness of output beam profile and extended depth of field, refractive field mappers may also be successfully used in combination with beam shaping optics of other operational principles. This combining makes it possible to improve drastically the performance of these beam shaping techniques. For example, the non-uniformity of the beam profile of many lasers leads to complexity and inconvenience in various beam shaping techniques based on applying spatial light modulators (SLM). Applications include Computer Generated Holography (CGH), holographic projection processing applications, holographic lithography, optical trapping and laser illumination in confocal microscopes. With a collimated flattop beam provided by refractive field mappers these techniques become easier to use, more effective and reliable in operation. This paper will describe some design basics of refractive beam shapers of the field mapping type, with emphasis on the features important for applications with SLMs. There will be presented comparative results of applying the refractive beam shapers in systems of holographic lithography and other techniques.

Gas lenses work on the basis that aerodynamic media can be used to generate a graded refractive index distribution which can be used to focus a laser beam. An example is a spinning pipe gas lens (SPGL). It is a steel pipe whose walls are heated to a preselected temperature and then rotated along the axis to any desired speed to generate a cooler core of incoming air. A laser beam propagating through these lenses is focussed in space. However, experimental observation has shown that distortions are generated in the beam. We provide a computational fluid dynamics (CFD) model of the lens and experimental results of the Zernike aberrations measured using a Shack-Hartmann wavefront sensor which show that the aerodynamic medium in the lens have a deleterious effect on laser beam quality (M²). The effect on the SPGL is that the beam deterioration increases with rotation speed and temperature though the worst M² measured at speed 20 Hz and temperature 155 °C was ~3.5 which is fairly good.

The femtosecond pulse quality in a laser system is determined by a non-compensated high-order dispersion and spectral deformation of the amplifier. A dispersive device that modifies the spectral amplitude and phase of the femtosecond pulse should be used to improve the duration of the compressed pulse and suppress the prepulses. The application of acousto-optical dispersive delay lines is considered. Different modifications of delay lines are compared and the types of devices used to shape femtosecond pulses are discussed. Several experimental dispersive delay lines were fabricated and investigated.

Beam shaping technology can greatly improve laser process efficiency by enabling parallel processes and increasing precision, quality and process stability. This paper outlines a system design, optical code analysis and the bench testing of a patented [1,2] laser beam homogenization and imaging system using prism beam splitting to produce a three spot array. The system uses a beam integrator to produce a rectangular spot that is split into three beams by two prisms. A second set of prisms directs the two outer beams onto an imaging lens and sets the pitch of the virtual spots. These beams, with the central beam, are imaged to form three spots with the required pitch. A prototype system design was developed for two approaches based on the first principles. The prototype system parameters were adjusted to minimize the requirements of the elements such as the imaging lens and prisms. Since the two systems require a relatively fast imaging lens, and there are aberrations associated with the prisms, a detailed optical design was conducted to determine the performance of the two approaches and to assess the complexity of the imaging lens. This paper will present the various positive and negative attributes of the two beam shaper designs within an optical system and how the best design was selected for prototyping and bench testing. Various data will be presented at each stage of design evaluation to the final bench test.

Bimorph mirrors for laser beam correction and formation were developed and investigated. Different types of substrates and active piezoceramics materials were considered to fabricate temperature independent shape of the mirror surface and to maximize the sensitivity of the mirror. High reflectivity coatings for different wavelengths were studied.

As in the case of zero-order Bessel beam being produced by illuminating an axicon with a Gaussian beam, higher-order Bessel beams are generated by substituting the Gaussian beam with a Laguerre Gaussian (LG) beam. These beams hold similar properties to zero-order Bessel beams except they carry orbital angular momentum (OAM). They also undergo an abrupt spatial transformation at the boundary of their non-diffracting regime whereby the near-field intensity distribution is a Bessel function which transforms into an annular ring (far-field profile). This can be considered a disadvantage to such beams in comparison to a Gaussian beam that is propagation invariant. By using a double axicon lens system this Bessel beams with z-dependent cone angles can be produced however at the expense of its non-diffracting nature. Here we outline an optical design to produce higher-order Bessel-like beams with z-dependent cone angles that will retains its spatial distribution as z→∞.

Within the paraxial framework, use of spiral phase elements is proposed for the shaping of light beams. More specifically, we analytically investigate some anisotropic optical devices for inducing controlled changes in several spatial and vectorial characteristics of light. As an illustrative example, depleted-center beams are considered.

We examine a novel method to control the orbital angular momentum (OAM) of lightwaves using forked polarization gratings (FPGs). We significantly improve the fabrication of FPGs and achieve substantially higher quality and efficiency than prior work. This is obtained by recording the hologram of two orthogonally polarized beams with phase singularities introduced by q-plates. As a single compact thin-film optical element, an FPG can control the OAM state of light with higher efficiency and better flexibility than current methods, which usually involve many bulky optical elements and are limited to lower OAM states. Our simulations confirm that FPGs work as polarization-controlled OAM state ladder operators that raise or lower the OAM states (charge l) of incident lightwaves, by the topological charge (l_g) on the FPGs, to new OAM states (charge l ± l_g). This feature allows us to generate, detect, and modify the OAM state with an arbitrary and controllable charge. An important application of FPGs are the essential state controlling elements in quantum systems based on OAM eigenstates, which may enable extreme high capacity quantum computation and communication.

Ultraviolet (UV) technology holds promise as a low cost non-thermal alternative to heat pasteurization of liquid foods and beverages. However, its application for foods is still limited due to low UV transmittance (LUVT). LUVT foods have a diverse range of chemical (pH, Brix, Aw), physical (density and viscosity) and optical properties (absorbance and scattering) that are critical for systems and process designs. The commercially available UV sources tested for foods include low and medium pressure mercury lamps (LPM and MPM), excimer and pulsed lamps (PUV). The LPM and excimer lamps are monochromatic sources whereas emission of MPM and PUV is polychromatic. The optimized design of UV-systems and UV-sources with parameters that match to specific product spectra have a potential to make UV treatments of LUVT foods more effective and will serve its further commercialization. In order to select UV source for specific food application, processing effects on nutritional, quality, sensorial and safety markers have to be evaluated. This paper will review current status of UV technology for food processing along with regulatory requirements. Discussion of approaches and results of measurements of chemico-physical and optical properties of various foods (fresh juices, milk, liquid whey proteins and sweeteners) that are critical for UV process and systems design will follow. Available UV sources did not prove totally effective either resulting in low microbial reduction or UV over-dosing of the product thereby leading to sensory changes. Beam shaping of UV light presents new opportunities to improve dosage uniformity and delivery of UV photons in LUVT foods.

A novel laser beam shaping system was designed to demonstrate the potential of using high power UV laser sources for large scale disinfection of liquids used in the production of food products, such as juices, beer, milk and other beverage types. The design incorporates a patented assembly of optical components including a diffractive beam splitting/shaping element and a faceted pyramidal or conically shaped Lambertian diffuser made from a compression molded PTFE compounds. When properly sintered to an appropriate density, as an example between 1.10 and 1.40 grams per cubic centimeter, the compressed PTFE compounds show a ~99% reflectance at wavelengths ranging from 300 nm to 1500 nm, and a ~98.5% refection of wavelengths from 250 nm to 2000 nm [1]. The unique diffuser configuration also benefits from the fact that the PTFE compounds do not degrade when exposed to ultraviolet radiation as do barium sulfate materials and silver or aluminized mirror coatings [2]. These components are contained within a hermetically sealed quartz tube. Once assembled a laser beam is directed through one end of the tube. This window takes the form of a computer generated diffractive splitter or other diffractive shaper element to split the laser beam into a series of spot beamlets, circular rings or other geometric shapes. As each of the split beamlets or rings cascade downward, they illuminate various points along the tapered PTFE cone or faceted pyramidal form. As they strike the surface they each diffuse in a Lambertian reflectance pattern creating a pseudo-uniform circumferential illuminator along the length of the quartz tube enclosing the assembly. The compact tubular structure termed Longitudinal Illuminated Diffuser (LID) provides a unique UV disinfection source that can be placed within a centrifugal reactor or a pipe based reactor chamber. This paper will review the overall design principle, key component design parameters, preliminary analytic and bench operational testing results.

Recent events concerning H1N1 "swine flu", have demonstrated to the world the significant potential of rapid increases in death and illness among all age groups and even among the healthy population [1] when a highly infectious influenza virus is introduced. In terms of mass casualties due to a pandemic, preparedness and response planning must be done. One course of action to prevent a pandemic outbreak or reduce the impact of a bioterrorist event is the use of isolation or quarantine facilities. The first level of isolation or quarantine is within the personal residence of the person exposed or infected. In the case where, the specific virus is extremely contagious and its onset of symptoms is rapid and severe, there will be a need for the deployment and setup of larger self contained quarantine facilities. Such facilities are used to house infectious individuals to minimize the exposure of susceptible individuals to contagious individuals, especially when specialized care or treatment is required and during the viral shedding period (5 to 7 days). These types of facilities require non-shared air conditioning, heating and ventilating systems where 100% of air is vented to the outside through a series of disinfection systems and staged filters. Although chemical disinfection is possible, there is a desire to incorporate intense UV radiation as a means to deactivate and disinfect airborne virus within hospital settings and isolated mass scale quarantine facilities. UV radiation is also being considered for disinfection of contaminated surfaces, such as table tops, walls and floors in hospitals and temporary quarantine facilities. In such applications the use of UV bulb technology can create many problems, for instance bulb technology requires numerous bulbs to treat a large volume of air, generates significant heat, uses significant power and does not produce large fluxes of UV light efficiently. This paper provides several methods of creating quarantine level disinfection systems using high intensity UV laser sources instead of UV bulb techniques by using laser beam shaping optics in conjunction with traditional optical laser beam delivery techniques.

We report on an axially asymmetric beam shaping optical system including a diffraction grating. This optical system compensates the astigmatism introduced by change in wavelength of a light source or change in ambient temperature. The phase function of the diffraction grating is determined to minimize the astigmatism by equalizing variation in distance from a light source to an image point on xz plane and variation in that distance on yz plane. This beam shaping optical system relates to a laser printer having an axially asymmetric profile.

In the near field region, optical antennas can generate local hot spots with high energy density. It can be very useful in increasing the photon-matter interactions for bio-sensing applications. There are several important bio-molecules having signature frequency (vibrational resonance) matching the mid infrared region of the optical spectrum. Thus mid-infrared antenna integrated with Quantum cascade laser (QCL) is highly desirable as it is currently considered to be one of the most efficient mid-infrared laser sources with a huge gamut of commercial applications. Here, we present a novel metal-dielectric-metal (MDM) based plasmonic nanorod antenna integrated on the facet of a room temperature working Quantum Cascade Laser. Simulations showed that at an optimized SiO₂ thickness of 20nm, the antenna can generate a local electric field with intensity 500 times higher than the incident field intensity. Further, it can increase the number of regions with local hot spots due to a higher number of geometrical singularities or sharp edges present in the MDM structure. This feature can be extremely useful, especially for bio-sensing applications. All device structures have been optimized based on 3d finite-difference timedomain (FDTD) numerical simulations. The antenna was fabricated on the facet of QCL using focused ion beam (FIB). The integrated plasmonic QCL has been measured using an apertureless mid-infrared near field scanning optical microscopy (a-NSOM). The measurement set-up is based on an inverted microscope coupled with a commercially available Atomic Forced Microscopy (AFM). We have experimentally found that such integrated nano antenna can generate a very narrow optical spot size, much below the diffraction limit, with high power density that matches well with the simulation results.

We experimentally examined the effect of laser energy fluence on the ablation of a silicon wafer using a Ti:sapphire femtosecond laser system. A femtosecond laser was focused through an oxide-metal-oxide (Al₂O₃/Al/Al₂O₃) film engraved with a subwavelength annular aperture (SAA) structure, i.e., a Bessel beam composed of a femtosecond laser created using a SAA. The optical performance, such as depth-of-focus (DOF) and focal spot of the SAA structure, was simulated using finite-difference time domain (FDTD) calculations. We found that a far-field laser beam propagating through the SAA structure possesses a sub-micron focal spot as well as high focus intensity. The experimental results demonstrated that silicon can be ablated using an input ablation threshold of an order of 0.05 J/cm² with a pulse duration at around 120fs. We found the obtained surface hole to have a diameter smaller than 1μm. Different surface ablation results obtained by using different threshold fluences of input laser energy are shown. Possible applications of this technique includes executing high aspect ratio laser drilling for thin film microfabrication, undertaking thru silicon via (TSV) for 3DIC, etc.

Laser leveling devices provide accurate positioning grid line in construction and building area. Multiple methods have been developed to transform a single Gaussian laser beam into full circle spreading grid line. In this paper, we devote to design and fabricate a most uniform and inexpensive capillary bundle design for construction engineering applications.

The regular spatial filters comprised of lens and pinhole are essential component in high power laser systems, such as lasers for inertial confinement fusion, nonlinear optical technology and directed-energy weapon. On the other hand the pinhole is treated as a bottleneck of high power laser due to harmful plasma created by the focusing beam. In this paper we present a spatial filter based on angular selectivity of Bragg diffraction grating to avoid the harmful focusing effect in the traditional pinhole filter. A spatial filter consisted of volume phase gratings in two-pass amplifier cavity were reported. Two-dimensional filter was proposed by using single Pi-phase-shifted Bragg grating, numerical simulation results shown that its angular spectrum bandwidth can be less than 160urad. The angular selectivity of photo-thermorefractive glass and RUGATE film filters, construction stability, thermal stability and the effects of misalignments of gratings on the diffraction efficiencies under high-pulse-energy laser operating condition are discussed.

We study the propagating and shaping characteristics of the novel one-dimensional Cartesian Parabolic-Gaussian beams. The transverse profile is described by the parabolic cylinder functions and are apodized by a Gaussian envelope. Their physical properties are studied in detail by finding the 2n-order intensity moments of the beam. Propagation through complex ABCD optical systems, normalization factor, beam width, the quality M² factor and its kurtosis parameter are derived. We discuss its behavior for different beam parameters and the relation between them. The Cartesian Parabolic-Gaussian beams carry finite power and form a biorthogonal set of solutions of the paraxial wave equation in Cartesian coordinates.

In this paper, the pulse shaping and diffraction properties of multilayer reflection volume holographic gratings under ultrashort pulse with arbitrary shapes in time are investigated using the modified multilayer coupled wave theory. Bragg diffraction of a system of multilayer reflection volume holographic gratings (MRVHG) is derived, and simple analytical expressions for the spectrum and spatial profiles of the transmitted and diffracted beams are obtained. Numerical results of the pulse shaping and diffraction properties of this system are also illustrated for several different temporal shapes. Results show that the temporal shapes of the input pulsed beams have been found to be an important factor in the analyses of the pulse shaping and diffraction properties of MRVHG. The analysis and observations of this paper will be valuable for optimizing the design and for novel applications of optical elements based on multilayer volume gratings.

The depth of penetration is probably the most important factor that influences the quality of a laser weld. The depth strongly depends on the focus of the welding beam. The sublimating material forms plasma vapors, that act as a lens and defocus the laser beam. Our contribution presents a method to compensate this phenomenon using an adaptive mirror - a mirror with flexible surface that can adjust the shape of the welding beam. The mirror is regulated by a feedback control loop so that the focus of the laser beam and the penetration depth remain in an optimal range. Since the only possibility to state the penetration depth is to monitor outer effects to estimate desired parameters. a sensor unit is used to monitor the optical emissions of the plasma vapors and the measured data are inputs to an algorithm that estimates the penetration depth. We have done several experiments that study the relation of the adaptive mirror focus and the laser beam shape and how it influences the penetration depth. The estimation results are compared with material samples from test welds. On the basis of these experiments, a preliminary version of a control system was developed and a tested. The tests has shown that the implementation of the control system has positive influence on the quality of the resulting weld.

We investigate optical solitons propagating through a nondiffracting Bessel photonic lattice. The transverse intensity pattern of the lattice can be adjusted through a shape parameter, inducing and changing an azimuthal modulation. We study how this modulation can stabilize transversal motion around a light ring of the lattice and characterize the different dynamics of motion.

We propose the fabrication and characterization to bending and temperature of a long period fiber grating with the alternative electric arc method known as fattening. This is the enlargement of the fiber structure by means of arc discharges from a commercial splicing machine. The fiber structure consists of 4 layers of glass of different refractive index. The resulting device is a reject band filter with an attenuation band around 1400nm. It has a bandwidth of 162nm with a depth around 26.9 dB. Test to bending depict changes in band depth up to -10dB between radii values of 4-7cm with a shifting span of 16.8nm. Temperature characterizations are made with bending and straight fiber over a hot surface. Interesting achievements can take advantage as optical sensors with different characteristics. Optimization in the fabrication process can be achieved to lower the insertion losses so better sensors can be applied for industry and commercial applications.

When a metal horizontal pipe is heated and spun along its axis, a graded refractive index distribution is generated which is can be used as a lens, thus its name, the spinning pipe gas lens (SPGL). Experimental results showed that though increase in rotation speed and/or temperature resulted in a stronger lens and removed distortions due to gravity, it also increased the size of higher order aberrations resulting in an increase in the beam quality factor (M²). A computational fluid dynamics (CFD) model was prepared to simulate the aerodynamics that show how it operates and, in the process shed some light on the optical results. The results of the model consist of velocity profiles and the resultant density data and profiles. At rest the cross-sectional density profile has a vertical symmetry due to gravity but becomes rotationally symmetric with a higher value of density at the core as rotation speed increases. The longitudinal density distribution is shown to be parabolic towards the ends but is fairly uniform at the centre. The velocity profiles show that this centre is the possible source of higher order aberrations which are responsible for the deterioration of beam quality.

We proposed a novel beam combining technique for coherent laser arrays that uses a conjugate Dammann grating (CDG) and a phase plate. By using this technique, a coherent laser array can be not only coherently combined to a single beam but also aperture filled to a far field single central lobe beam by means of phase compensation in theory. The aperture size and power density of the combined beam can be conveniently changed. Moreover, the technique applies for both binary and continuous amplitude profiles emitted from an individual laser of laser arrays, especially Gaussian beam. An verified experiment with a simulated 5×5 coherent laser array using an aperture mask was performed that effectively verified the feasibility of the proposed concept. This new method has the potential for scaling to much higher output powers with good beam quality by coherent combination and aperture filling of coherent laser arrays in practical applications.

In high power laser systems, the high-frequency noise generated by nonlinear effect is effectively removed by low-pass spatial filter, and the low-frequency noise passing through pinhole is always considered as very safe to optical devices in downstream. However, in practical applications both modulation contrast ratio and spatial frequency of the low-frequency noise will be changed and possibly become dangerous components, depending on different magnification ratios of spatial filter. In this paper, the evolution of low-frequency noise is theoretically analyzed and numerical simulated depending on different magnification ratios of spatial filter. The analysis results show that both modulation contrast ratio and spatial frequency of the low-frequency noise passing through pinhole will be changed 1/M times, where M is magnification ratio of spatial filter. For M<1, the safe low-frequency noise will be extruded into high-frequency which is the fastest growing components and finally develop into the most dangerous part to the damage of optical devices again. It is significant to consider the evolution of low-frequency noise in practical applications of spatial filter for high power laser system.

Ytterbium doped silica fibers exhibits very broad absorption and emission band, from ~800 nm to ~1064 nm for absorption and ~970 nm to ~1200 nm for emission according to the cavity length. A wide range of applications for tunable ytterbium fiber laser like development of single-frequency sources for spectroscopic applications, pumping source of Pr: ZBLAN amplifier and Tm: ZBLAN up conversion laser, material processing and military applications. In this paper, a 976 nm high power fiber coupled diode laser of up to 5 W end pumped ytterbium doped multimode D-shaped fiber laser using Fabry-Perot cavity with different regime of operation with the output coupler reflectivities of 80%, 60%, and Fresnel reflection of 4%. The output laser wavelength ranges from 1041 nm to 1094 nm for a cavity length from 1 m to 10 m, respectively. The optical to optical slope efficiency of 45% at 1 m and increased to be 60% at 4 m cavity length were measured. The maximum slope efficiency of 82.12% at cavity length of 2m were investigated with Fresnel reflection output coupler, and the measured lowest threshold pump power for this configuration was 130 mW. Also, the self-pulsation phenomena were observed just at higher pumping power of more than 4W and its threshold pumping power were (4.3W, 4.5W and 4.7W) with output coupler reflectivities of (80%, 60%, and Fresnel reflection of 4%), respectively at 10 m fiber length.

Here we investigate closed-loop adaptive optical system to compensate for laser beam aberrations. A bimorph mirror is used as a wavefront corrector and Shack-Hartmann wavefront sensor is an element for feedback control. Comparison of phase conjugation and multi-dither technique is shown.