The PDF file contains the front matter associated with SPIE Proceedings Volume 11107 including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

Perfect (optical) vortices (PVs) have attracted significant interest in the optical community owing to their well-defined annular ring whose near-field radial profile is independent of orbital angular momentum (OAM). Although it is a general belief that it is not possible to perform quantitative OAM measurement of PVs by modal decomposition, here we show, both theoretically and experimentally, that the OAM content of a PV can be measured quantitatively in both the near- and far-fields, including superpositions of OAM within one perfect vortex. Our work will be of interest to the large community who seek to use such structured light fields in various applications, including optical trapping and tweezing and optical communications.

One of the challenges for every optical system is preserving the quality of the used beam, which may be significantly reduced, due to the low condition of used optical elements or their misalignment. There are plenty of methods focused on correction of the final beam, depending on the used entire optical system. Problem of efficient beam evaluation is just as important. So far, most of the measurements, are based on visual inspection, which is not always enough, especially when the high quality of the beam is required. Novel approaches use structured light to increase beam sensitivity for any imperfections. In this paper we present approach, which uses optical vortex shifted off-axis for a beam quality measurement. It uses SLM as a vortex generating element, which is shifted off-axis by proper hologram transformation. Tracking of the vortex trajectory may provide information about beam quality and aberration of optical system. The new vortex localization algorithm will be presented.

We demonstrate a random fiber laser with cylindrical vector beams (CVBs) emission. A 9-km-long fiber is applied to form one of the laser mirrors providing random distributed feedback (RDFB). Due to the RDFB provided by the ultralong fiber, mode competitions are well suppressed in the cavity leading to the laser output with modeless behavior. A mode selective coupler (MSC) inserted in the cavity is used to achieve the mode conversion from fundamental mode to cylindrical vector modes. By adjusting the mechanical polarization controllers carefully, both azimuthally and radially polarized beams are achieved with high mode purity. The designed laser retains many advantages of the random lasers, such as low cost and modeless output. The CVBs with modeless behavior may be useful in many practical applications such as biomedical imaging, laser radars and free space communication.

We present an experimental setup to generate partially coherent Ince-Gaussian beams. The partially coherent field is constructed using a rotating ground glass disk to reduce the spatial coherence of a laser source and digital holograms. Our results show that the cross correlation function of these beams inherit properties of their spatial structure. The experimental cross correlation function is measured by means of a well known wavefront folding interferometer, which allows us to characterize the properties of the beam. The comparison between theoretical and experimental results yields excellent agreement.

Wavefront shaping is a technique that uses phase or amplitude modulation to create desired wavefronts on light in optical systems. Wavefronts which are properly conjugated will refocus after reflection from a rough surface. This refocusing effect is called reflective inverse diffusion. There currently are two different wavefront shaping techniques used to achieve reflective inverse diffusion: iterative methods and matrix methods. Iterative methods find one phase front which allows for reflected light to be focused at a single, specific position, with results that are immediately available and continuously improving. Matrix methods calculate the complex matrix which describes the rough surface and allow for reflected light to be be refocused at many positions after reflective inverse diffusion and at multiple spots simultaneously. However, matrix methods are susceptible to decreased performance in a noisy system, and their results are not available until the entire matrix is measured. A new alternative method for reflective inverse diffusion combines non-mechanical beam steering principles with an iterative method’s phase front, giving it the multiple-spot capabilities of matrix methods. Utilizing an optical Fourier transform relationship in the reflective inverse diffusion setup, the shift theorem of Fourier transforms creates phase tilts at the sample on top of the conjugating phasefront when the phasefront from the SLM is translated in position. The phase tilts at the sample steer the reflected focused beam. Translations of an iterative method’s phase front using circular shifts steer the reflected spot at the cost of decreased enhancement with a larger shift.

Techniques for optical trapping and micromanipulation, as well as precision drilling, have resulted from the ability to generate different types of Bessel beams. A standard method for producing Bessel intensity profiles involves an annular slit and focusing lens. The fixed geometry of this optical system only allows the generation of a particular Bessel beam with specific propagation properties. To increase the flexibility of a conventional annulus-lens configuration, we introduce a fluid-based method for modifying the core diameter and propagation properties of zero-order Bessel beams. In our optical set-up, Bessel beams are created with a HeNe laser operating at 543 nm with an output power of 4 mW. An annular slit is placed at the front focal plane of a lens with f = 25 cm. A transparent, custom-built container composed of three fluid chambers, each 5 cm in length, is placed after the lens. Our experiments make use of two fluids: water (n = 1.33) and vegetable oil (n = 1.43). Without using any fluids, at a propagation distance of 50 cm from the lens, our set-up produces a Bessel beam with core diameter = 0.231 mm. When the beam passes through a sequence of oilair-water, the core diameter at the same distance increases to 0.241 mm. We also observe an extended maximum propagation distance for a beam that travels through this combination of media. Modification of Bessel beam propagation properties is consistent with a change in effective focal length brought about by refraction through the liquid components.

The intra-distance between laser-induced modifications is the limiting factor of glass dicing speed and efficiency. In this work, we present a novel method for the generation of directional cracks in the bulk of glass to enhance the dicing performance. The asymmetrical Bessel-like laser beams with a long non-diffractive length were formed by filtering their spectra of spatial frequencies. Experiments were carried out using the mJ-level laser source with sub-nanosecond pulse duration. The dicing process was optimised by varying processing parameters. The flexural strength of the modified material was measured using the four-point bending setup. Results showed that asymmetrical intensity distribution enables higher dicing speed, better cleavability and quality, compared to symmetrical Bessel-like laser beams.

Femtosecond (fs) laser beams may be shaped into Bessel beam (BB) profiles by spatial light modulators or axicon lenses. Temporally reshaping laser pulses by chirping and stretching further alters the spatio-temporal intensity pattern within the elongated focal volume. Such beam shaping applied to high-power pulses is useful for numerous materials processing applications, enabling fabrication of very high aspect ratio columns in optically transparent materials. We report the development of a compact, adaptable microscope turret-mounted assembly containing an axicon and a high numeric aperture aspheric lens imaging system, and the use of temporal reshaping studies in various fs laser machining applications. Depending on axicon angle, lens separations, and the refractive index of the substrate, the central lobe diameter of the BB may be less than 1 μm but extending over 500 μm long, effectively forming a narrow, long cylindrical column. Moreover, because an entire column can be machined with a single, energetic pulse, high processing rates are possible. Materials such as fused silica and polymers are found to be good candidates for directly formed voids. Microchannels in silica can be used in single-molecule recycling experiments, while permeable membranes in thin plastics are sought for cellular studies, passing nutrients but not cells. In rigid crystalline structures like diamond and sapphire, the substrate material is transformed in place. In particular, a BB column machined through electrically insulating diamond can become conductive graphite, which is of interest for developing radiation-hard detectors of highenergy particles.

Laser beam shaping is a venerable topic and has seen implementation by a range of solutions, for example, static solutions in the form of refractive and diffractive optics, as well as dynamic solutions by adaptive optics and spatial light modulators. Recently geometric phase elements have come to the fore based on liquid crystal technology and metamaterials. All of these solutions are expensive and slow. Here we outline recent progress in the use of digital micro-mirror devices (DMDs) for real-time laser beam shaping and control. We demonstrate >1000 Hz creation of both scalar and vector beams of arbitrary design, and illustrate how to use this technology to mimic real-world beam perturbations such as thermal aberrations and turbulence.

In this paper, a MEMS mirror driver ASIC that operates a 1D MEMS mirror with accurate amplitude is presented. It provides a set of position signals, precisely aligned to the MEMS mirror that enables a beam forming and laser shooting scheduling for LiDAR (Light Detection and Ranging) applications. The proposed architecture exploits a capacitive sense method and integrated control loops to sense, actuate and control the movements of the MEMS mirror. The implemented mixed-signal ASIC is fabricated in 130 nm CMOS technology, and can attain an RMS pointing error of less than 4m°for any tested MEMS mirror amplitude.

We investigate the distortion caused by the differences between the working environment and the mounting temperature in the surface shape of the deformable mirror (DM) used in the National Ignition Facility. The characteristics of the surface distortion appeared on the DM under different temperature fields, such as the uniform and gradient working environment temperature, are studied in theory and experiments. Under the uniform working environment temperature, the distorted surface shape reveals the high-frequency and actuator-corresponding characteristics. The distorted surface shapes and their dependence on the actuators’ distribution and structural parameters of the DM are analyzed by using the finite element method. The analysis on the distorted surface shape under the gradient working environment temperature indicates that the changes of the peak and valley (PV) or root-mean-square (RMS) value rely on the temperature gradient as well as the difference between the mirror and the environment with a certain rule. To compensate the temperature induced surface shape distortion (TID), its essential mechanism is analyzed systematically based on the thermal stress characteristics, which shows that the actuators’ tilt caused by the thermal expansion coefficient difference between the mirror and the steel base is the essential reason. An efficient method based on an auxiliary temperature compensation module (TCM) and a hybrid closed-loop control algorithm (HCLA) are presented accordingly. In the simulation and the experiment, the DM’s TID could be effectively depressed and a well-compensated DM surface shape is finally achieved.

The most important part of any adaptive optical system is a deformable mirror. One of the most widely used type of such mirrors are the bimorph ones. In fact, there is no problem to manufacture a wide aperture bimorph wavefront correctors that perfectly can compensate low-order laser aberrations. But if one needs a tiny deformable mirror to correct for high order aberrations with reasonable amplitude, he usually will use stacked actuator mirror or a MEMS one. In this presentation we suggest the new design and technology of production of a small size bimorph mirrors to be used to correct for atmospheric phase fluctuations. Our mirror has the diameter of 30 mm and 37 control electrodes (mirror with 20 mm and 63 control electrodes is being developed). The resonance frequency of 13.2 kHz is due to its small diameter. At the same time, large number of electrodes allows to reproduce high order aberrations. To manufacture this device two modern technologies are used: ultrasonic welding and laser engraving technology.

In this work, we investigate the efficiency of the use of the bimorph deformable mirror to focusing laser beam in the pinhole. Pinholes of different diameters are used as an instrument for focusing verification. Different algorithms are discussed and analyzed for the investigation of the process of the beam focusing. It is shown that tip-tilt correction is an essential condition for increasing the focusing efficiency.

The Shack-Hartmann wavefront sensor (SHWFS) is widely used in an adaptive optics (AO) system to measure the wavefront. The measurement accuracy of the SHWFS is limited by the micro-lens array, which is a core component of it. A deflectometry system (DS) is constructed to offer a high resolution measurement for the AO system, which could be used to test the surface shape of the deformable mirror (DM). The configuration and principle of the DS are presented. The surface shape testing and close-loop performance are analyzed in simulation and experiment. Results show that the DS has good ability in surface shape testing and close-loop correction.

The laser marking method has obvious advantages over other available marking methods in speed, accuracy, and flexibility. Mask marking and beam deflection marking are typical methods, each having advantages and disadvantages. In the former, an opaque mask is directly imaged to create the desired mark. This method is practical and relatively fast, but most of the marking energy is blocked, losing efficiency. Additionally, this method requires a precise and bulky lens system. In the latter method, the focused beam is steered onto the sample, writing point by point. This technique has higher flexibility between marks, but it is slow, requires micro-movements, and accurate micro-motion parts are very expensive. We propose an innovative, holographic approach in laser marking. In the new system, a holographic projection system based on a digitally designed computer-generated hologram (CGH) is employed. This specially designed, fully transparent, phase only CGH modulates the high-power writing beam to create any desired image in the far field, where the beam etches a permanent mark of that image onto the designated silicon wafer substrate. Holographic marking combines the advantages of mask and beam deflection marking methods, such as high speed and stationary operation with minimal power loss, in a relatively simple and inexpensive setup. Also, since the holographic projection maintains its image quality after a certain distance, the setup is less prone to spatial alignment errors. We believe that the proposed technique will make significant contributions in the field of laser marking.

The optical intensity profile of a laser beam is crucial in laser micromachining and laser ablation mass spectrometry (MS). For the latter, Gaussian laser beams are usually used to probe surfaces of material and obtain two-dimensional (2D) maps of their compositions. Such 2D MS analysis can be extended into the third dimension (3D) if the probe is able to remove homogeneously thin layers of material by each laser shot. This high depth resolution of the probe is difficult to achieve with Gaussian beams because they cannot produce flat bottoms of ablated craters. To better understand laser ablation MS experiments aimed at enabling and optimizing this capability, studies of laser ablation of silicon under ambient conditions with flat-top and Gaussian beams generated by a femtosecond 800 nm laser with increasing incidence angles and numbers of laser shots were conducted. The resultant craters were characterized via optical 3D microscopy. When the beam profile was flat-top, the ablation rate was homogenized over the laser beam spot so that flat crater bottoms were achieved over a wide range of incidence angles. This enables 3D MS analysis with laser ablation probes, with ablation rates approaching <1 nm per shot, significantly steeper crater walls and minimal surface damage in comparison to the Gaussian craters. Flat bottom near-cylindrical and “splash-like” conical crater geometries observed in these experiments indicate that ablation regimes for the flat-top and Gaussian profiles, respectively, were different despite using similar laser energies.

Industrial lasers used for materials processing have become essential tools in a wide array of applications, including cutting, welding, drilling, cladding, marking, hardening, and additive manufacturing. The speed, quality, and process window are determined in part by the laser beam properties such as beam size, shape, and divergence. nLIGHT has developed a new multi-kilowatt fiber laser, Corona™, that provides rapid tunability of the beam characteristics directly from the laser output fiber using a novel, all-fiber mechanism. Programmable beam shapes include flat top and donut beams with beam diameters from 100 μm to 390 μm and beam parameter products from 3 to 20 mm-mrad (M² values from 9 to 59). We describe the Corona fiber laser performance and show processing results and advantages of specific beam shapes for sheet-metal cutting, the largest industrial laser application.

High precision multibeam processing is a useful approach to increase the productivity of high precision laser material processing by means of ultrashort pulsed (USP) laser radiation. In the field of micro- and nanostructuring multibeam ultrashort pulsed laser processing attracts increasing attention due to its ability to generate periodic pattern like filters within an economically reasonable time of up to 12.000 holes/sec. Thus, this technology has become relevant for applications in the filtration industry and biotech industry. The developed multibeamscanner (MBS) is capable of drilling holes with extremely small outlet diameters (< 1μm) into various materials with a customized arrangement and a density of more than 10.000 holes per mm². The aim is to investigate how the exit diameter of single-digit sized holes can be further reduced using the multibeamscanner and whether an increase in productivity is possible.

Talking about purified assembled printed circuit boards (PCBs), e.g. in automotive industry for control of airbag or antilock braking systems (ABS) one of the main issues is the protection against environmental impact. The error-free functionality has to be guaranteed even under extreme conditions and this warranty has to be provided for even a decade.

The process of conformal coating is not new but nowadays manufacturer of PCBs starts to use the conformal coating process not only at selected areas, the full board is going to be protected. To keep the costs under control it is inevitable to measure the thickness of the coatings. An intelligent design of the full process chain implementing the conformal coating process are perfect conditions to integrate sensor technology for process control.

This feature will describe the implementation of an optical sensor technology for the inspection of the conformal coating process to illustrate the benefit of optical sensors in today's industry.

A high-energy, dual-pulse, injection seeded pump laser operating at 1064 nm is an enabling technology for several airborne and space-based trace gas lidar systems. In a NASA SBIR funded Phase I effort we performed proof of principle testing of an approach to building such a laser. During Phase I, we successfully demonstrated the following key technical objectives.

1. Operation of a single-frequency oscillator that achieved high beam quality, 30 mJ dual-pulse output at 50 Hz. The 30 mJ pulse pairs had an M² of 1.5 and a pulse spacing of 100 μs. Our current approach to dual pulse operation allows pulse spacings in increments of 100 μs. Future implementations will increase the flexibility of the pulse spacings.

2. Efficient amplification of the dual-pulse oscillator output with existing in-house amplifiers to 120 mJ each while still maintaining an M² of 1.9.

3. Further amplification of the output with a traditional on-axis Brewster angle slab to 280 mJ/pulse with an optical-to-optical efficiency of 18%. We anticipate achieving >20% efficiency in the future by incorporating an updated off-axis amplifier design.

In the next development phase, our goal is to mature the technology and demonstrate a path to a space-qualifiable, injection-seeded laser system capable of producing two closely spaced (~100-200 μs), 600 mJ pulses at 50 Hz.

Tabletop plasma-driven X-ray lasers hold the promise to overcome beamtime limitation of accelerator facilities. Such unlimited access is essential for training purposes, industrial processes as well as for going beyond the "proof-of-principle" research. Tabletop X-ray lasers are demonstrated by single-pass amplified spontaneous emission (ASE) across a plasma medium by means of transient collisional excitation. The latter is either a discharge or a laser-produced plasma obtained by target material irradiation. The homogeneity of the plasma medium is crucial to minimize refraction or self-absorption. Generation of ASE across a plasma column is dramatically improved under traveling-wave excitation (TWE). This means that a pump laser pulse irradiates a target with a certain angle of attack, instead of classical normal incidence. In the latter case hot spots and cold spots are formed. In the case of TWE a single sweep of plasma is formed in the same direction of pump pulse. The latter is optimized when the sweep propagation is close to the speed of light (i.e the ASE speed), which implies small-angle of attack. Yet, short-wavelength plasma lasing needs large-angle target irradiation, in order to increase the pump penetration into the denser plasma core. High electron density is needed for high collisional pumping rates. The apparent tradeoff large angle (for short wavelength) vs small angle (for efficient gain) was solved by pulse shaping, i.e. pulse-front back-tilt. In fact, the TWE speed depends on the pulse-front slope (envelope of propagation front), whereas the optical penetration depth depends on the wavefront slope (envelope of phase). Pulse-front tilt was accomplished by means of pulse compressor misalignment ("easing"). The latter is the final stage of a chirped-pulse amplification (CPA) system that recompresses the stretched pulse. In this study it was found effective to use the easing of the compressor, only if coupled with a high-magnification frontend imaging/focusing component, and that higher order terms are marginal. It is concluded that sweep speed matching should be accomplished with minimal compressor misalignment of a few degrees and maximal imaging magnification. A complete computational study by means of Fourier Optics was performed and validated experimentally.

Directed energy (DE) systems composed of large numbers of combined laser beams have been proposed for a number of applications, including illumination of photovoltaic cells on the moon and spacecraft propulsion. It is important to understand how the design parameters of these systems and perturbations such as misalignment and phase error affect their performance. It is also useful to evaluate the effects of phase and amplitude screens. This paper describes the development of a tool that can simulate the beam profile of over ten billion coherently combined laser elements at astronomical distances with user set locations, mode fields, amplitudes, phases, and pointing vectors.

We evaluate the feasibility of implementing a polarization diverse scheme to facilitate beacon based phase locking of a long baseline laser phased array.

We evaluate the performance of a 10 W CW Ytterbium doped fiber amplifier system operating at 1064 nm suitable for use in a laser phased array directed energy system. The amplifier is optimized for use in a beacon based phased array topology.

The Higher order Poincar´e sphere (HOPS) is generally used to describe scalar and vector orbital angular momentum modes. These modes have found many applications to date; however, they are limited to low power levels. It has thus become topical to consider amplification of such structured light modes. Here, we study the purity of the HOPS beams in a master oscillator power amplifier configuration using recently developed characterization tools through birefringent and non-birefringent amplifiers. We outline a general theory for this problem where we consider both gain and vector perspectives, and confirm our theory by experiment.