This PDF file contains the front matter associated with SPIE Proceedings Volume 12667, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Optical vortices carrying orbital angular momentum and with durations of femtoseconds recently have attracted great interest due to their potential applications in ultra-fast spectroscopy, high-intensity field physics and ultrafast optics through a new degree of freedom that they add to nonlinear optics.Thus, developing compact and efficient tools for their generation is required. Here, we present a reflective multi-material phase converter with high conversion efficiency over a broad wavelength range (over 200 nm) and high damage threshold that works directly with a Gaussian beam, common to most mode-locked lasers. Additionally the device allows to compensate dispersion previously acquired by the incident pulse. Spatio-spectro-temporal numerical simulations showing viability of the device are presented.

This paper presents a method for achieving 2D beam steering using 16-phased array grating couplers through FDTD simulation. The method begins by designing a single grating coupler with a silicon nitride material (depth = 0.15 um, width = 0.2 um, grating pitch = 0.34 um) to achieve 1D beam steering of around 7.6° by changing the input wavelength from 500 nm to 550 nm and changing the TE or TM mode source. The grating pitch of 0.34 um was selected because the input wavelength at 532 nm through the NV center can measure the magnitude field, resulting in a reflected angle of 0°. By changing the input wavelength, positive and negative beam steering directions can be achieved. Subsequently, a total of 16 phased arrays were established, and a multimode interferometer (MMI) was used to split the input beam into 16 grating couplers. With the 16 waveguides, the phase can be changed from 0 to π/8, allowing the 2D steering angle to be altered from 0° to 1.72°. The method was validated using 3D simulations to ensure that the results match those obtained through 2D simulation.

Here we present an innovative free-space optical (FSO) communication system which is capable of training database in real-time and demultiplex multiplexed spatial structured laser beams such as orbital angular momentum (OAM) beams under varying atmospheric turbulent conditions. The core part of our detection system is heterogeneous convolutional neural network includes an optical 4f system using first Fourier convolution neural network layer driven by kilohertz-fast reprogrammable high-resolution digital micromirror devices (DMDs). This optical-filtering-based convolutional neural network is utilized to realize the training and demultiplexing 4-bit OAM-coded beams under simulated turbulent condition using modified von K´arm´an atmospheric model. The current implementation shows classification accuracy of 89.35% (under weak turbulence) and 38.26% (under strong turbulence).

In this work, we propose a new sensitive polarization optical security system. This system takes advantage of the unique and interesting properties of polarization holograms, which can encode polarized complex fields. The system is controlled by an interface, which has three defined parameters and a target image. These parameters are compared with the parameters obtained of the PH Fourier diffraction intensity pattern and recovered field. We present experimental results to probe the effectiveness of the system.

Laser is widely used in industry, biomedical and other kinds of fields. Beam size is the most important parameter among the laser variables. Typical state-of-the-art profiling techniques employ either a scanning-based or camera-based system, using photodiodes or image sensors as the signal receiver. Despite their profiling capabilities, these systems do not tend to be budget-friendly and easy to operate. In this paper, a novel cost-effective beam profiling prototype based on self-mixing interference was developed to measure the Full Width Half Maximum (FWHM) of a range of laser diodes by the knifeedge approach. The difference between our prototype and other systems is that the photodiode is placed behind the laser source, and beam size is calculated by analyzing the feedback signal. A commercial camera beam profiler was used to benchmark our prototype. Results show that though there is a variation of 45.29% between the measured beam size and the integrated beam size in the x directions due to diffuse and specular reflection, our USD 200 prototype has a high accuracy on the prediction of laser beam sizes. Our prototype could provide accurate predicted beam size for Gaussianalike beam. This is the very first study to explore the application of self-mixing interference in laser beam profiling. It is believed that our proposed approach has contributed to the on-going development of laser beam profiling methodology.

Digital micromirror devices (DMDs) are wavelength and polarization independent, have a faster response rate and are affordable- making it a prime beam shaping tool for the commercial world. However, due to its micro-mirror structure and encoded grating, DMDs diffract and disperse broadband light. Although this dispersion problem has been addressed before, the solutions presented require expensive optics and or precise alignment, making it costly and impractical for commercial use. In this work we propose a simple and easily implementable solution that requires a single lens. We then demonstrate this experimentally by generating broadband modes in the image plane.

Optical Wireless Power Transmission (OWPT) system, using beam shaping, is a promising technology that involves a transmitter side using a laser and a receiver side using solar cells to transfer power wirelessly over long distances. The system faces a challenge of potential mismatch between both sides, which can lead to low efficiency of power transfer. The objective of this research is to improve the mismatch between the beam shape of a semiconductor laser light source and the shape of a photodetector solar cell. The shape of a typical solar cell is rectangular, which does not match the circular beam shape of the light source, resulting in lower power conversion efficiency. To address this, methods have been proposed to beam shape into a rectangle using Fresnel lenses or rectangular core optical fibers. However, the distance from the solar cell and the rotation of the solar cell itself change the size of the beam, resulting in a trapezoidal image as seen from the light source. In this study, we report the results of an evaluation of the change in efficiency with respect to changes in the object, using a spatial light modulator (SLM) that can arbitrarily shape the light beam. Specifically, we evaluate how adjusting the shape of a circular beam onto a solar cell target using the SLM leads to a decrease in photocurrent, and how recognizing an object's beam shape in real-time to control a camera using machine learning can predict object shape for error suppression compared to linear prediction.

In this work, we report on the results obtained using a multibeam direct-write laser lithography technology for the fabrication of sub-micron photonic structures. This approach uses a state-of-the-art tool that simultaneously offers highthroughput and high-resolution fabrication capabilities for scalable nanotechnology applications. We demonstrate the capabilities of the multibeam laser lithography by optimizing and fabricating an anti-dot array. We show that our technology is capable of producing structures with feature sizes as small as 300 nm with high fidelity and uniformity. Moreover, we investigate the influence of various parameters, such as laser power, and focus settings on the resolution and quality of the fabricated structures. The potential of the multibeam laser lithography is further demonstrated for the exposure of large surface areas by fabricating a 12 cm x 12 cm photonic crystal array with critical dimensions of 600 nm. The uniformity and periodicity over the entire area are both investigated by extensive metrology, demonstrating high scalability. Overall, our results highlight the potential of multibeam laser lithography as a powerful method for industrial scale nanotechnology. The technique offers great versatility, making it an ideal tool for various applications in various fields of optics, from wafer-level integrated photonics to photonic bandgap structures, and from displays to large area Xray optics.

Grayscale lithography produces three-dimensional (3D) photoresist profiles versus the standard two-dimensional lithography. Grayscale lithography is fully compatible with standard nano- and micro-fabrication deposition and etching techniques, enabling a wide range of applications, e.g., micro-lenses or micro-fluidic ramps. In order for grayscale lithography to work, the resist is only exposed partially (versus fully for standard lithography). This partial exposure can be achieved by various methods; two examples are: (i) the use of a so-called high-energy beam sensitive (HEBS) photomask, or (ii) a grayscale photomask with a projection stepper. Diffuser-based grayscale lithography, as shown in our original work [1], circumvents many of these disadvantages, but our earlier method has a fundamental limitation: sharp resist edges cannot be patterned because the diffuser will “smear” out any edge feature causing rounding in the resist profile. In this paper, we extend our original method to enable transfer of grayscale resist profiles into substrates with sharp edges and corners. The basic idea of the newly proposed advanced approach is rather straightforward and effective: adding a buried metal mask to the diffuser-based gray-scale method. Furthermore, we decrease the roughness of the resist by using holographic diffusers; these are diffractive optical elements that transform beams into a defined shape with homogenized distribution.

Free-electron laser beam quality can be degraded due to microbunching instability (MBI) caused by collective quantum electrodynamic effects. A Laguerre-Gaussian mode laser profile has been shown to significantly reduce MBI compared to the standard Gaussian profile under ideal conditions. However, practical limitations of accelerators significantly hinder the Laguerre-Gaussian profile’s performance. We propose the use of a Bessel-Gaussian mode profile for laser heating. We model the interaction between the laser heater and e-beam with various spatial profiles and compare the Bessel-Gaussian with the Gaussian and Laguerre-Gaussian modes. We showcase the Bessel-Gaussian beam’s immunity to jitter and consistent suppression of MBI.

The emission limits and the rulesets in the international laser safety standard IEC 60825-1:2014 are based on scientific evidence from damage threshold experiments and simulations. However, available data sets of laser-induced damage experiments for specific parameter spaces are limited. Therefore, further determination of damage thresholds for laser systems, operating in these parameter spaces, is crucial. Retinal damage thresholds are determined with experiments using animal tissue and optical setups with pulsed lasers and beam profiles of constant irradiance. Several factors influencing these experiments, such as the focusing were identified. This work investigates the biological variability of porcine tissue samples by minimizing the influencing factors and performing damage experiments.

The next generation of ultra-bright photoemission sources may offer opportunities to enhance our understanding of fundamental spatiotemporal scales. However, modeling photoemission and laser shaping systems precisely and efficiently is difficult due to the numerous interdependent linear and nonlinear processes involved and significant variations in modeling frameworks. Here, we present a new machine learning-based framework for photoemission laser systems and dynamic laser shaping. To showcase the effectiveness of our approach in system optimization, reverse engineering, and design. Our framework is designed to facilitate precise adaptive temporal shaping, including the generation of longitudinally flat-top or periodically-modulated pulses, through integration with four-wave mixing.

Spherical aberration is a common phase distortion that occurs in optical elements. An optical beam passing through an element that has spherical aberration will accrue a quartic phase term. Here, we provide an analytical analysis of the effect of the quartic phase on the beam quality factor of Laguerre-Gauss beams. We find that the beam radius is a critical parameter in determining the effect of the aberration on the quality of the laser beams.

In this paper, we explore the collimation quality of collimated Gaussian beams generated via the deployment of engineered diffusers. Various aspects of beam propagation through engineered diffusers are explored using results from carefully designed experiments. Raw Gaussian beam is incident on a sample engineered diffuser. The beam is then collimated and propagated over several meters to clearly estimate beam divergence for different test cases. These test cases include raw and focused beams incident on engineered diffusers, the effect on collimation with the use of speckle reducers, and the evolution of the collimated beam wavefront during propagation. To measure and document the spatial coherence properties of beam propagation and its spatial coherence properties after propagating through the engineered diffuser, we measure the beam profile with knife-edge measurement, CCD imaging, and Shack-Hartmann sensor-based wavefront measurements along the beam propagation path. We do so for all different type of beam conditioning before incidence at the engineered diffuser – this includes analyzing the effects of a speckle reducer in the system. We present detailed experimental results and parameters of the propagating collimated beam in the paper. We hope that this paper will lay foundations for our understanding of using engineered diffusers for short distance free-space optical links using a beam collimation approach which is several times optically efficient than a pinhole based spatial filtering-based beam collimation approach.

The semi-automatic system for laser beam alignment was developed and researched. The alignment system was used to make the laser beam follow the predetermined path through the optical scheme (basically a series of reflective surfaces such as mirrors or lenses). The algorithm and the software to control the system was developed and tested. The system contained of diode laser source, two gimbal mirror mounts with stepper motors, multi-axis motion controller, near field sensor, far field sensor, wavefront sensor, and control software. It allowed to control the positioning of the beam, tip-tilt and overall curvature of the wavefront.

The adaptive optical system with phase-only spatial light modulator and CCD intensity analyzer were assembled and tested. The experimental results of formation of the flattop and doughnut-like intensity distributions were presented. Up to 75 % of the initial energy were concentrated inside the target shape of the far field.

The reduction of cross-sectional area of actuators from 4*4 mm² to 2*2 mm² in cartridge-type piezostack deformable mirror was investigated. Harmonic analysis showed that stroke of the actuators with 16 mm² and 4 mm² was equal 5.33 and 5.52 microns correspondingly in case of interdigital commutation of layers. However, the mechanical stiffness of such actuators was low. To increase robustness of wavefront corrector a gap structure for inner electrode configuration was used. The piezoceramic cartridges with cross-sectional area of individual actuator with 2*2 mm2 was produced. The local stroke of single piezostack was 4.6-4.8 microns per 300 V.

To increase the cost-effectiveness of the piezostack deformable mirror we proposed to use the modular design of such wavefront correctors. Each module contains 5 individual multilayer actuators with size of 4*4 mm. The performance of 50*50 mm cartridge-type piezostack deformable mirror with 100 control elements was investigated. Main parameters of the developed wavefront corrector were estimated such as the local stroke, influence functions, the control bandwidth.