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This work presents an experimental study to emulate solutions of Lippmann-Schwinger equations for scattering by an elliptical billiard. The probability density patterns are recovered in the intensity of a laser beam scattered by a Spatial Light Modulator (SLM). This result opens an interesting perspective to explore scattering solutions, mainly when physical distributions with specific properties are required. Optical simulations performed by experiments with intense laser beams have been applied for many quantum systems and in this work, we expand this application. • Optical simulation of solution of the Lippmann-Schwinger equation. • Different elliptical billiard is explored for hologram construction. • Probability density distribution for scattering is emulated by a laser beam. • Remarkable agreement between optical and theoretical results. [ABSTRACT FROM AUTHOR]

• High-throughput additive manufacturing of bioinspired superhydrophobic surfaces. • Two orders of magnitude higher efficiency than standard two-photon polymerization. • Fabricated surfaces enable micro reactions and lossless droplet manipulation. Bioinspired functional surfaces have attracted considerable attention within multiple scientific and industrial fields. In particular, the hollow hierarchical structure and chemical heterogeneity endow Salvinia leaves with superhydrophobicity and underwater air retention capability. However, replicating complex three-dimensional Salvinia-like patterns at the microscale currently relies on time-consuming additive manufacturing methods, preventing their wide adoption in industrial applications. Here, we report a high-throughput femtosecond laser direct writing strategy based on the quadrifurcate abruptly autofocusing beam for the single-exposure fabrication of Salvinia-like microstructures. Combined with chemical functionalization, both the hollow morphology and heterogeneous chemical properties of the natural counterpart were mimicked. The obtained bioinspired surfaces can repel and manipulate water droplets, and maintain superhydrophobicity even immersed underwater. The proposed single-exposure fabrication strategy is expected to contribute to the mass production of Salvinia-inspired surfaces, whose unique wetting properties promise great potential in chemical engineering, micro bioanalysis, and microfluidic devices. [ABSTRACT FROM AUTHOR]

The ideal spherical holographic display promises an expanded field of view, which allows for observation from all angles. However, challenges still exist in the spherical holographic display, primarily stemming from the planar modulator and the holographic distortion. Here, a color spherical holographic display system based on conformal diffraction principle is proposed. The core components of the system include a color laser and a spatial light modulator loaded with spherical holograms. A synchronous sequential controller is developed to achieve color dynamic holographic display. Furthermore, the conformal diffraction principle is proposed to generate distortion-free holograms. Based on the principle, the recorded object is characterized as a conformal spherical object, and a precise correspondence between the hologram and the spherical reconstructed image is established. By leveraging the proposed system, the full-color high-quality spherical holographic display with expanded viewing angles can be realized, which can flexibly adapt to different holographic display scenes. The proposed system advocates the application of spherical holographic display and has potential applications in several fields. • A system is proposed to achieve realistic holographic display on a spherical surface. • A conformal diffraction principle is proposed for precise hologram generation. • A sequential controller is developed for dynamic color holographic display. [ABSTRACT FROM AUTHOR]

Two-photon-polymerization is an additive manufacturing method to produce parts with high resolution. With reachable voxel sizes below the optical diffraction limit, it is of particular interest for biomedical or micro-optical applications. Despite its high resolution, the spreading of this method is hindered by its low productivity in the µm³/s range. Scaling up productivity is in principle possible with already available laser sources with high pulse energy and beam shaping such as multi-spot approaches. This beam shaping is limited in the processable volume and has to be expanded to arbitrary beam shapes in three dimensions to make use of the next generation laser sources with higher pulse energy and higher average laser power. In this work, a three-dimensional Iterative Fourier Transform Algorithm for optimizing arbitrary three-dimensional intensity distributions using a spatial phase modulator was investigated for suitability for 2PP. [ABSTRACT FROM AUTHOR]

Spatial Light Modulators are widely used for creating multiple laser spots with a flexible spatial distribution. This work presents an optical setup for multi-spot laser micro-drilling on stainless steel. For decreasing the hole diameter and getting high laser spot intensities, Bessel beams were generated. A phase only SLM was used as a beam splitter and a physical axicon was added to the setup. This separation of beam splitting and shaping is due to the higher diffraction efficiency of the axicon compared to holographic generated Bessel beams, especially for high cone angles. Minimizing the intensity losses is important due to the low damage threshold of SLM displays. Furthermore, additional lenses has been added for increasing the spot intensity. An ultra-short pulse Ti:Sa-laser (800 nm, 100 fs) was used for the experiments. Possible Bessel spot distributions for metal processing and the impact of the mutual influence of the spots were investigated. [ABSTRACT FROM AUTHOR]

• Utilizes phase encoding of input images as an alternative to conventional holography for recording object information. • Clear reconstructed images can be obtained at the observation plane by irradiating the SLM with a reference light. Computer-generated holography is a technique that utilizes computers and algorithms to generate holographic images. Deep learning-based Computer-generated holography can learn the mapping relationship between input images and holographic images, which offers faster computation speed and better image quality comparing with direct encoding and iterative optimization methods. However, most methods typically employ stacked convolutional layers to expand the receptive field, which leads to a sharp increase in computational cost as well as number of parameters. We proposed a rapid computer-generated holograms method with lightweight local and global self-attention networks (LGSANet), which performs phase encoding of input images as an alternative to the conventional holographic method for recording object information. Once the network training is completed, it is possible to perform high quality holograms with a spatial resolution of 1920 × 1080 within 39 ms. By importing the encoded phase of input images into a spatial light modulator (SLM), a clear reconstructed image can be obtained at the observation plane by irradiating the SLM with a reference light (@λ = 532 nm). Experimental results show the proposed method exhibits significant improvements in peak signal-to-noise ratio (PSNR) and structural similarity index (SSIM), as well as reduced speckle noise, which can be applied to holographic displays, AR/VR, metasurface design, medical imaging, etc. [ABSTRACT FROM AUTHOR]

• Operational limit of a cooled spatial light modulator extended from P=110 W to 210 W with picosecond laser exposure. • Binary Damman arrays with π phase range enhance SLM performance, achieving η ∼ 0.77 at 183 W. • Introduction of efficient flat top intensity (FT) generator reduces chip temperature while SLM phase response reaches Δ φ > 2π at P=210 W with an 8 x 8 mm FT beam. • Enhanced diffractive performance on stainless steel allows multi-beam ps laser processing efficiency η ∼ 0.89 at 183 W. The phase range of a Spatial Light Modulator (SLM) requires full 2 π response for accurate phase modulation of the incident laser wavefront to create the desired structured intensity distribution. While cooled SLM's allow increased power exposures, degradation in performance occurs with average powers P > 100 W in a Gaussian beam due to residual absorption and consequent heating of the liquid crystal (LC) layer which seriously limits the phase stroke and diffraction efficiency. By introducing a refractive flat top intensity generator ahead of a cooled SLM, we have extended the phase range to Δ φ = 2 π at incident power P=210 W with only a small light field depolarisation. The operational limit has therefore been extended significantly, allowing efficient, parallel laser materials processing with a high-power picosecond laser. The calculation and implementation of binary Damman gratings for multi-beam laser processing is also shown to be useful at high power exposure. [ABSTRACT FROM AUTHOR]

• Characterization of statistical properties of a vector source requires fast and efficient measurement of all four elements of the square coherence-polarization (BCP) matrix. • We have developed a new experimental technique to measure all four elements of the BCP matrix from a single-intensity recording. • A detailed theoretical framework is presented to measure the elements of the BCP matrix of vector source through polarization correlation of the first two Stokes parameters (SPs), S 0 and S 1. We validate our technique through numerical simulations followed by proof-of-principle experiments for three different vector sources. • In our experimental demonstration, a tuneable beam displacer realizes the measurement of two SPs, S0 and S1 in a single-frame and use these parameters to extract the BCP matrix of spatially fluctuating random vector fields. A good agreement between simulation and experimental results confirms the accuracy of the proposed technique. • A primary advantage of our experimental design is its ability to ascertain all four elements of the BCP matrix from a single measurement. Moreover, absence of QWP and LP offers some new advantages in the experimental measurements. Characterization of statistical properties of a vector source requires fast and efficient measurement of all four elements of the square coherence-polarization (BCP) matrix. Here, we report a new experimental technique for measuring the BCP matrix of the stochastic field using a single-intensity recording. A detailed theoretical framework is presented to measure the elements of the BCP matrix of vector source through polarization correlation of the first two Stokes parameters (SPs), S 0 and S 1. We validate our technique through numerical simulations followed by proof-of-principle experiments. Experimental demonstration is performed by employing a specially designed folded interferometer to coherently sum a vector random field with a known reference and subsequently leverage a tuneable beam displacer to capture the orthogonal polarization components to determine the first two SPs in a single-frame recording. A correlation of these two SPs and their Fourier processing enables the extraction of all four elements of the BCP matrix from a single-intensity recording. The viability of our experimental technique is demonstrated by measuring all four elements of the BCP matrix for three different vector sources in the far-field. A good agreement between simulation and experimental results confirms the accuracy of the proposed technique. This method will find applications in the characterization of light fields, evaluating the polarization dynamics, looking through randomness, etc. [ABSTRACT FROM AUTHOR]

Femtosecond laser pulses were spatially modulated with fast reconfiguration of computer-generated holograms (CGHs) using a ferroelectric liquid-crystal-on-silicon spatial light modulator (FLCoS-SLM). Reconfiguration was executed at a frame rate of more than 1 kHz while changing the CGH every frame. The CGHs were designed as binary phases because the FLCoS-SLM can represent only binary values. The optimization method was modified by the weighted iterative Fourier transform algorithm (IFTA) to make the binary phase. The fundamental performance of the CGH reconstruction and femtosecond laser processing with 6.3 kHz pulse-to-pulse spatial light modulation was demonstrated. The reconfiguration speed will drastically change the applicability to science and industrial fields and open a door for new CGH applications. • Femtosecond pulses were modulated with CGH reconfiguration of 6.3kHz using FLCoS-SLM. • To our knowledge, this is the highest frame rate for laser processing using LCoS-SLM. • To make the binary phase mask, the weighted IFTA was modified. • The fast reconfiguration speed will be useful for next-generation laser processing. [ABSTRACT FROM AUTHOR]

• · A cost-effective digital laser configuration with dual-phase modulation using only single Spatial Light Modulator. • Dynamically generating high-quality vortex beams, Laguerre-Gaussian modes, with tunable orbital angular momentum. • A dual-phase modulation expanding the possibilities for intracavity beam shaping in Digital lasers. The development of digital lasers is limited by the fact that digital laser cavities can only provide a round-trip single-time intra-cavity phase modulation for the oscillating light field in the laser cavity, which limits the capability of generating structured light fields, such as light field type and quality. This paper presents a digital laser configuration of a cost-effective laser cavity design for generating orbital angular momentum (OAM) laser beams, which provides two controllable intra-cavity phase modulations by utilizing a single spatial light modulator (SLM). The experiments demonstrated that high-quality vortex beams with controllable OAM and intensity profiles are successfully generated in the proposed digital laser by employing dual spiral phase modulation in the laser cavity. The vortex Laguerre-Gaussian mode of topological charge value from 1 to 5 of high mode purity over 90% are obtained experimentally in this study. With two controllable intra-cavity phase modulations, this novel digital laser design not only presents a flexible solution for tailored OAM beam generation, but also extends the possibilities for advancing the generation of complex structured beam with digital lasers. [ABSTRACT FROM AUTHOR]

• A novel method for high-dimensional image encoding is proposed that uses two spatially separated polarization components of C-point vector beams. • The proposed approach harnesses the unique characteristics of light carrying spatially concatenated orthogonal states of optical vortices for image encoding. • The utilization of optical vortices associated with orbital angular momentum offers flexibility in terms of allowing for the selection of infinite integer values of topological charge. • Manipulation within two degrees of freedom of light is demonstrated through a non-interferometric experimental set-up employing dual-pass modulation approach. Considering the concern of efficient data handling in information security applications, we propose a novel method for high-dimensional image encoding onto two spatially separated polarization components of C-point vector beams. These beams, known for their spatially varying polarization distribution are generated by the superposition of different magnitude of optical vortex modes modulated into orthogonal polarization basis. Our approach harnesses the unique characteristics of light carrying spatially concatenated orthogonal states of optical vortices for image encoding unlike traditional optical cryptosystems that rely on the spatial distribution of amplitude, phase, and polarization of light. Through the superposition of phase holograms corresponding to images encoded within both the polarization components, each exhibits distinct magnitudes of optical vortex modes at each pixel. The proposed approach allows for secure image encryption into C-point vector beams. The utilization of optical vortices associated with orbital angular momentum offers flexibility in terms of allowing for the selection of infinite integer values of topological charge. This versatility inspires us to encode image using an array of vortices, thereby ensuring stable encoding and minimize quality degradation in practical implementations. Furthermore, exploiting the two orthogonal polarization components of light enhances high-dimensional encoding, offering a solution to the 'capacity crunch' issue in secure optical communication systems. Manipulation within two degrees of freedom of light is demonstrated through a non-interferometric experimental set-up employing dual-pass modulation approach which simplifies vector beam generation. [ABSTRACT FROM AUTHOR]

Optical transmission through atmospheric turbulence is a critical issue for establishing optical communication based on photonic spatial degrees of freedom. Refractive index fluctuations by a turbulent atmosphere cause structural distortion on the transmitted laser beams, resulting in crosstalk between adjacent spatial modes. We study a deep-learning technique to compensate for the turbulence effect. In particular, we mainly focus on improving the correction performance according to the selection of a probe beam. Different modes of Laguerre-Gaussian beams, including the lowest order (Gaussian), are employed as optical probes, and their abilities to compensate for turbulence effects are compared. Our results show that the Gaussian probe beam achieves a higher average correlation coefficient and a lower error rate, i.e., better correction performance, despite the spot size smaller than higher-order modes. Finally, to demonstrate the origin of the performance difference, we examine residual phases by spatial position and discuss the correction coverages. • A generative model for correcting atmospheric turbulence is presented. • Different modes of Laguerre-Gaussian beams are employed as optical probes. • Correction performance for each probe beam is comparatively analyzed. • The importance of spatial analysis on correction performance is discussed. [ABSTRACT FROM AUTHOR]

• A pixelated polarization calibration approach is proposed to enable efficient and precise programming of spatially-varying linearly polarized light. • The proposed approach is further verified by the implementation of the Pancharatnam-Berry (PB) lens with the focusing efficiency of 85.58 % for the circularly polarized light. The resolution of the fabricated LC planar optical elements with the proposed setup can reach 1.54 μm. • The proposed liquid crystal spatial light modulator (LC-SLM)-based exposure system can enable arbitrary alignment patterns fabrication for LC molecules with only one single exposure step, providing great potential for vectorial light field generation and LC-based planar optics. The use of liquid crystal spatial light modulator (LC-SLM) to manipulate the polarization of the light has been widely explored for different applications, including optical field manipulation, maskless lithography, polarization imaging, and LC planar-optics, among others. Precise polarization manipulation of LC-SLM is therefore highly demanded. Here, we introduce a high-efficiency approach for calibrating the polarization manipulation of a parallel-aligned LC-SLM. The approach revolves around the primary calibration criterion, the degree of polarization (DoP). Through parameter optimization to generate the calibration grayscale, a remarkable DoP as high as 97 % can be attained, with a sustained DoP level of up to 93.7 %. Experimental results showcase outstanding DoP uniformity in the modulated beam achieved with the calibrated LC-SLM. The root mean square error (RMSE) of polarization for modulated light from LC-SLM is about 0.018. A pixelated polarization calibration approach is proposed to enable efficient and precise programming of spatially-varying linearly polarized light (SVLPL), which can be further verified by the implementation of the Pancharatnam-Berry (PB) lens. The resolution of the fabricated LC planar optical elements with our setup can reach 1.54 μm. The programmable SVLPL with high DoP and resolution is potentially useful for many applications in planar optics and vectorial optical field manipulation. [ABSTRACT FROM AUTHOR]

• A fine optimization of aberration compensation method to enhance the encircled energy inside a silicon wafer is proposed and demonstrated. • The distribution effect of flyback regions that correspond to the laser intensity distribution is taken into consideration. • 38.4% improvement in crack propagation of stealth dicing is achieved compared with conventional correcting method. Stealth dicing is widely utilized in wafer manufacturing due to its excellent advantages, such as debris-free and narrow kerf width, over the conventional process dicing method. Aberration compensation is the key technology for achieving high quality and efficiency in stealth dicing. A fine optimization of aberration compensation method is proposed here to enhance the energy intensity near the focusing point inside a silicon wafer. This method takes into account not only the impact of the total number of flyback regions on focusing, but also their distribution on the SLM. Instead of relying on minimum peak-to-valley value, it employs the focus intensity reduction value to quantify the impact of flyback regions. To demonstrate this method, simulations of intensity distribution in silicon wafer were performed along with an experiment to evaluate dicing performance using crack propagation. After employing our correcting method, the maximum crack propagation increased to 58.7 μm and resulted in a 38.4 % improvement in dicing performance compared to the conventional correcting method. [ABSTRACT FROM AUTHOR]

• A SLM-assisted ns-laser processing technique is proposed for fabricating large-area, uniform, and well-arranged periodic structures on Cr films. • 2. For 1000-nm thick Cr films, the processed surface exhibits hybrid periodic microstructures comprised by modulated grating (MG) and laser induced periodic surface structures (LIPSS), that is, MG-LIPSS, which displays vivid anisotropic structural colors. • 3. For 200-nm thick Cr films, the processed hybrid structures are a combination of MG and cracks, that is, MGC, which can be utilized as a transmission grating with diffraction effects. An effective technique for preparing different hybrid periodic structures on chromium (Cr) films of different thicknesses using a 1064-nm nanosecond laser assisted by spatial light modulator (SLM) is proposed. For 1000-nm Cr films, by combining periodic modulated grating (MG) patterned by SLM with laser-induced periodic surface structures (LIPSS), regular dual-scale MG-LIPSS can be fabricated, with the morphological characteristics controlled by laser fluence, effective pulse number, and MG period. Due to diffraction effects of MG and LIPSS, MG-LIPSS patterned surfaces exhibit vivid anisotropic structural colors. In contract to MG-LIPSS, complex periodic structures consisting of MG and cracks (MGC) are fabricated on 200-nm Cr films due to the more significant thermal stress of a thinner film. Although the cracks of MGC distributed randomly, MGC show a long-range order characteristic with a certain transmittance, which can be utilized as a transmission grating with diffraction effects. These results demonstrate that optical field modulated laser machining based on SLM offers an efficient, cost-effective, and controllable method for fabricating large-area periodic structures on Cr films. Moreover, variations in film thickness can be employed to explore hybrid microstructures with specific properties, and thus utilized in diverse applications, such as optical components and anti-counterfeiting measures. [ABSTRACT FROM AUTHOR]

• A holographic two-photon microscope was developed for dual-plane imaging. • A spatial light modulator generated an additional focal plane. • A temporal multiplexing strategy allowed fast imaging of two different focal planes. • 4-D imaging was achieved at cellular resolution and physiological timescales. • 4-D imaging and analysis will facilitate studies linking structure and function. Spatiotemporal patterns of neural activity generate brain functions, such as perception, memory, and behavior. Four-dimensional (4-D: x , y , z , t) analyses of such neural activity will facilitate understanding of brain functions. However, conventional two-photon microscope systems observe single-plane brain tissue alone at a time with cellular resolution. It faces a trade-off between the spatial resolution in the x -, y -, and z -axes and the temporal resolution by a limited point-by-point scan speed. To overcome this trade-off in 4-D imaging, we developed a holographic two-photon microscope for dual-plane imaging. A spatial light modulator (SLM) provided an additional focal plane at a different depth. Temporal multiplexing of split lasers with an optical chopper allowed fast imaging of two different focal planes. We simultaneously recorded the activities of neurons on layers 2/3 and 5 of the cerebral cortex in awake mice in vivo. The present study demonstrated the proof-of-concept of dual-plane two-photon imaging of neural circuits by using the temporally multiplexed SLM-based microscope. The temporally multiplexed holographic microscope, combined with in vivo labeling with genetically encoded probes, enabled 4-D imaging and analysis of neural activities at cellular resolution and physiological timescales. Large-scale 4-D imaging and analysis will facilitate studies of not only the nervous system but also of various biological systems. [ABSTRACT FROM AUTHOR]

The generation of non-diffracting beams often requires solving complex partial differential equations, e.g., Maxwell's equations or Schrödinger equation. This poses a significant challenge when it comes to developing new types of non-diffracting beams. In this study, we propose a general phase transfer function that can be used with a spatial light modulator (SLM) in a high numerical aperture (NA) system to generate a family of non-diffracting light beams. Using this approach, we have successfully generated a self-rotating quasi-non-diffracting beam based on the general phase transfer function. We have conducted numerical simulations to study the performance of these self-rotating quasi-non-diffracting beams, which have shown unique features, such as self-rotation and independent control of waist diameter and depth of focus. These features have the potential to advance various applications, including optical imaging and manipulation of biological targets, optical fabrication, and optical communication. [ABSTRACT FROM AUTHOR]

In our earlier paper [Adamov, E. V., Aksenov, V. P., Dudorov, V. V., Kolosov, V. V., & Levitskii, M. E. (2022). Controlling the spatial structure of vector beams synthesized by a fiber laser array. Optics & Laser Technology , 154 , 108,351], we presented the method to control the spatial intensity distribution of a beam synthesized as a result of coherent combining of subbeams from an array of phase-controlled fiber radiation sources, each subbeam characterized by its own direction of linear polarization. In this paper, we consider theoretically and experimentally the feasibility of controlling the polarization structure of such synthesized beams by changing the phase relations between individual subbeams. It is shown that for fixed polarization directions of the subbeams, the nonuniform polarization distribution of the synthesized beam, whose character depends on the phase relations and polarization directions of the subbeams, can be controlled via a change of only subbeam phases. • In our earlier paper [Adamov, E. V., Aksenov, V. P., Dudorov, V. V., Kolosov, V. V., & Levitskii, M. E. (2022). Controlling the spatial structure of vector beams synthesized by a fiber laser array. Optics & Laser Technology , 154 , 108,351], we presented the method to control the spatial intensity distribution of a beam synthesized as a result of coherent combining of subbeams from an array of phase-controlled fiber radiation sources, each subbeam characterized by its own direction of linear polarization. In this paper, we consider theoretically and experimentally the feasibility of controlling the polarization structure of such synthesized beams by changing the phase relations between individual subbeams. It is shown that for fixed polarization directions of the subbeams, the nonuniform polarization distribution of the synthesized beam, whose character depends on the phase relations and polarization directions of the subbeams, can be controlled via a change of only subbeam phases.. [ABSTRACT FROM AUTHOR]

[Display omitted] • The experimental proof of concept is demonstrated for the first time to realize racemic helical metamaterials with 4 + 1 beams double exposure phase-controlled laser interference lithography. • The tapering in the helix metamaterials has been proposed to be introduced by varying interference angles between 4 + 1 beams in 1st and 2nd exposure. • The proposed metamaterial has been numerically investigated for optical modes and its coupling phenomena between the opposite-handed helix adjacent to each other in a square unit cell. • The racemic helical metamaterial has been demonstrated numerically as a potential platform for tailored circular dichroism and acts as broadband omnidirectional plasmonic absorber suitable for optoelectronic applications. In this study, we propose a double exposure phase-controlled laser interference lithography (DE-PCLIL) approach in 4 + 1 beams interference to design a three-dimensional (3D) racemic helical periodic nanostructure. The explicit azimuthal rotation of each beam by π/2 between the two exposures and the resultant intensity distribution discover the racemic 3D helix structure arranged in the square unit cell. The proof of concept is experimentally demonstrated by recording a series of cross-sectional images at different z-planes of the volumetric interference pattern on a CMOS camera using a spatial light modulator (SLM). Additionally, we propose an approach to realize tapering in such a geometry through a slight variation of the interference angle in both exposures. We numerically investigated optical modes and circular dichroism (CD) characteristics of the racemic helix metamaterial. The racemic helix metamaterial structure offers an angle of incidence and polarization-insensitive coupled mode. Through numerical studies, we propose an alternative way to bring 3.4-fold CD signal enhancement by varying the phase of a particular handed helix only through modulating the local chiral field. Such 3D structure is profound with perfect absorption in broad spectral regions, potentially suited for plasmonic absorber-based photovoltaic and photo-catalysis applications. [ABSTRACT FROM AUTHOR]

• The new digital shearography meets the requirements of high standards, making it suitable for dynamic tests while providing high-quality phase maps. • Both shearing direction and amount can be controlled quantitatively and accurately. • Phase maps can be evaluated with a single exposure. • High light efficiency and accurate phase demodulation lead to high-quality phase maps. Digital shearography (DS), a laser-based optical interferometric method, is widely employed for measuring the first-order derivative of an object's surface deformation. Unlike digital holography, DS integrates self-reference optics, enhancing resistance to environmental disturbance and improving detection sensitivity, making it ideal for non-destructive testing (NDT). DS finds applications in diverse fields such as material inspection, fluid property research, medical diagnostics, cultural heritage restoration, and military defense. The conventional temporal phase-shift (TPS) method encounters limitations in dynamic tests, leading to the introduction of the spatial phase-shift (SPS) method. However, SPS is restricted by aperture size, impacting the phase map quality. The spatial light modulator (SLM) introduces a novel approach to DS system development, enabling quantitative shearing adjustments through precise SLM control. Existing DS systems using traditional phase-shift technology rely on interferometers and struggle to achieve high-quality phase maps with a single exposure. The proposed high-performance DS, leveraging both SLM and a micro-polarizer camera, overcomes this limitation, facilitates single-exposure phase map evaluation with the polarization phase-shift technique, and eliminates the need for a tiny aperture, enhancing light beam utilization and phase map quality. [ABSTRACT FROM AUTHOR]

The up-scaling of laser micromachining processes with ultrashort pulses is limited due to heat accumulation and shielding effects. Multi beam scanning represents one of the strategies to overcome this drawback. It is in general realized by combining a diffractive beam splitter with a galvanometer scanner. A full synchronization with the laser repetition rate offers new possibilities with minimum thermal impact. We will demonstrate this by means of a multipulse-drilling on the fly process with a regular 5x5 spot pattern having a spot to spot spacing of 160µm. At a repetition rate of 100 kHz and an average power of 16 W we were able to drill more than 2'300 holes/s in a 10µm thick steel foil. We have further extended this technology with a special light modulator for different periodic spot patterns and more complex intensity distributions. [ABSTRACT FROM AUTHOR]

A spatial light modulator is used to flexibly shape and divide a femtosecond laser beam. The phase masks required for this task are generated by iterative algorithms like the well-known Gerchberg-Saxton-Algorithm (GSA). However, the GSA tends to generate phase masks containing singularities, leading to severe deviations from the desired target intensity distribution. To address this, a modified GSA was developed which avoids singularities and is capable of finding phase solutions being close to analytic ones in cases where they exist. Measurements of the corresponding intensity distributions are shown. The aim of this development is to parallelize micromachining with high-power USP-lasers. [ABSTRACT FROM AUTHOR]

[Display omitted] • A human-in-the-loop feedbacked 3D-GS algorithm was proposed to obtain coaxially distributed laser spots. • Magnifying effect of the observing optical route accelerated algorithm convergence. • A maximum 10 laser sub-beams were generated to successfully stealth dice JSG3 quartz glass. Cutting of transparent materials is of great importance. In this study, JGS3 quartz glass is cut with laser stealth dicing (LSD) method. By loading computer generated hologram (CGH), a spatial light modulator (SLM) modulates a laser beam into ten coaxial beams along the depth direction. A human-in-the-loop feedback-weighted three-dimensional Gerchberg-Saxton (3D-GS) algorithm is utilized to improve its performance. The effectiveness of the algorithm is verified by CCD-captured energy distribution records. A noticeable improvement in multi-beam energy uniformity is realized. Additionally, an qualitative analysis is conducted to investigate the changes of laser beams inside the glass during LSD. Through flexible tuning of multi-focus spacing, the laser-diced surface roughness could be adjusted and optimized to ∼1 μm, paving the way for future advanced applications. [ABSTRACT FROM AUTHOR]

Optical quantum logic gates are the basic elements for building optical quantum computer. Usually, to implement different logic gates, different optical elements and frameworks are needed. Here, we propose a versatile device that a modified Sagnac interferometer composed of a spatial light modulator (SLM) for implementing multiple optical gates within a classical light framework. We demonstrate that the device can manipulate the polarization and full-field spatial modes of photons to perform multi-qubit logic operations. And versatile conversions between different logic gates are achieved by simply altering the hologram imposed on SLM. Our device shows a good performance in exploring the photon's full degrees of freedom, which makes it an appropriate candidate for integrated optical computing. [ABSTRACT FROM AUTHOR]

A wavelength multiplexing with spectral supercontinuum source in computational ghost imaging is implemented and investigated. In our proof-of-concept experiment, we used two diffraction gratings and one spatial light modulator to form up to 10 independent spectral channels. Registration of data by a spectrometer in such a scheme makes it possible to reduce the time of data acquisition by a factor of ten. It was established that an increase the number of spectral channels from 1 to 10 leads to the increase of the contrast-to-noise ratio by the factor of 2.8. This makes the proposed technique attractive for high-speed demanding applications such as communications and remote sensing. • Multiple-wavelength multiplexing computational ghost imaging with spectral supercontinuum is demonstrated. • Practical aspects of the implementation of the experimental scheme are provided. • The quantity of channels proportional accelerates data acquisition. • Optimization of the formed random binary pattern sizes to improve the quality of object image reconstruction is performed. [ABSTRACT FROM AUTHOR]

• High-accuracy beam splitting by means of phase-only spatial light modulator. • Iterative Fourier transformation algorithm extended by machine learning methods and open camera feedback. • Black-marking of stainless steel using ultrashort pulse laser. Phase-only spatial light modulators are ideal for the generation of beam splitter profiles to parallelize a variety of laser processes. A novel approach for the calculation of phase holograms is proposed to achieve a highly accurate power distribution over all spots. The Iterative Fourier Transform Algorithm (IFTA) is extended by the use of different machine learning methods, which are trained in an open camera-feedback loop. After the training phase, improvement of the beam splitting accuracy is then validated experimentally. The advantage of the presented approach is shown by comparing it to the standard IFTA algorithm. Finally, use of the approach is demonstrated through metal marking with an ultrashort pulse laser. [ABSTRACT FROM AUTHOR]

Highlights • Most of the correction methods use visual inspection as a beam quality merit function. • Visual beam inspection is not sufficient when precise SLM application is needed. • Two quality criteria, based on more objective methods are proposed. • Detection of small deviation from ideal beam is possible. • Both can be applied in any system, where the beam intensity is recorded. Abstract Spatial light modulator (SLM) is a modern device extensively used for laser beam shaping. Over the years, its quality has been significantly improved. Nevertheless, there is still a need to correct its imperfections. In this paper we propose two criteria which allow to examine correction effectiveness of SLM. One is based on the Laguerre–Gauss transform and the second uses optical vortex dynamics which exposes a high sensitivity to any beam imperfections. It is based on the vortex internal scanning method, where the shape of vortex trajectory provides information about SLM correction quality. In this paper we test its sensitivity to astigmatism, which was introduced manually by SLM, after proper correction. [ABSTRACT FROM AUTHOR]

Highlights • The vortex phase rotates according to the phase shift introduced by a medium. • The rotation angle of the vortex can quantify the refractive index of liquids. • A system based on a spatial light modulator is built to retrieve the vortex phase. • Compared with a Michelson interferometer, the proposed system is more stable. • Extremely small differences in concentration, the order of 0.01%, is distinguished. Abstract We present a spatial light modulator (SLM) based phase shifting interferometry (PSI) using an optical vortex for sensing the refractive index (RI) of liquids. The vortex phase rotates according to the phase shift introduced by a medium, and its rotation angle quantifies the index of refraction of the sample. An interferometer modified with the SLM is designed to obtain reliable results. We experimentally demonstrate the stability of the SLM-based system by measuring interference and phase fluctuation. Experimental results show that the proposed system keeps the fluctuation small. The vortex probe PSI combined with the SLM-based interferometer enables not only detecting extremely small changes in concentration but also precisely measuring the RI with high resolution of ∼10−5 refractive index unit. [ABSTRACT FROM AUTHOR]

Highlights • The SLM can change the phase of the light and the amount of shear. • The nonlinear random error in phase shift method can be eliminated. • The efficiency of detection can be greatly improved. Abstract The paper presents a new shearography system which applies a spatial light modulator (SLM). The system can control the shearing amount and direction as well as introduce the phase shift accurately and automatically, making shearographic testing easier and more practical. Shearography has the known advantages for nondestructive test and strain measurements of being fast, full-field, and having high sensitivity. Traditionally, the shearing amount is controlled by adjusting a reflector mechanically. Mechanical adjustment of the reflector is slow, inconvenient and not well suited for in-field NDT practice. For application of phase shift techniques, a piezoelectric transducer (PZT), which is usually used for application of phase shift techniques, introduces random error due to its tendency to be nonlinear. This paper introduces a new shearographic detection system with a spatial light modulator. The spatial light modulator controls the liquid crystal by using a birefringence effect and twisted nematic effect. The spatial light modulator can change the phase of the light and shearing amount accurately and automatically, thus eliminating the nonlinear random error in the phase shift method. Furthermore, this system also improves testing efficiency. In this paper, the fundamental of SLM shearography is presented. The capability of this optical configuration is demonstrated theoretically as well as through experiments. [ABSTRACT FROM AUTHOR]

Highlights • A novel method of picosecond laser parallel processing with desired beam geometries and intensity by using two spatial light modulators is presented. • The desired parallel laser shaped beams with intensity are modified by polarization sensitive mask imaging combined with computer generated holograms (CGHs). • Observed shaping efficiencies with dimensions of the polarization sensitive mask images are discussed in detail. • The resulting complex light fields with uniform intensity were used to ablate a titanium substrate with uniform depth and high definition. Abstract An imaging based beam shaping technique combined with parallel beam processing has been demonstrated. Binary and intensity masks have been designed and applied on phase only spatial light modulator (SLM) to shape the input laser beam in the desired profile and intensity distribution. A second SLM with a computer generated hologram(CGH) applied was used to split the incident picosecond laser beam. Hence, the laser beam was effectively converted to required target shape, intensity distribution and a separated pattern then reconstructed at the image plane of a focusing lens. The machined footprints on a polished Titanium (Ti6Al4V) substrate accurately match the desired beam in shape and depth distribution. [ABSTRACT FROM AUTHOR]

Arc beam laser-induced forward transfer (AB-LIFT) based on an arc beam is a promising micro additive manufacturing process to efficiently prepare high-performance metal microcircuits by transferring metal microdroplets. Therefore, elucidating the transfer mechanism of arc-beam-induced microdroplets is crucial to controlling the printing process. In this paper, a dark-field imaging system is developed to visually analyze the transfer process of metal microdroplets, and the injection mechanism of Gaussian and arc-beam laser-induced forward transfer is analyzed. Meanwhile, by studying the deposition behavior of laser-induced forward transfer micro drops with an arc beam at a single pulse energy, it is concluded that the factors affecting the laser-induced forward transfer with an arc beam mainly include the center angle and diameter of the arc beam. Then the effects of the center angle and diameter of the arc beam and the laser parameters on the preparation of microcircuits by AB-LIFT are systematically investigated, and a set of process methods for the effective preparation of high-performance microcircuits is proposed. [Display omitted] • Developed a dark-field imaging system to visualize and analyze the transfer process under a small receiving gap. • Revealed the formation mechanism of Gaussian beam and Arc beam laser-induced forward transfer. • A set of process methods to effectively fabricate high-performance microcircuits. [ABSTRACT FROM AUTHOR]

• The paper reports the development of a new liquid crystal (LC) optical phase modulator that can lead to full 2 π phase modulation combined with response times that are on the order of 1 ms. • Full 2 π phase modulation can be achieved at driving voltages that are readily accessible using existing silicon backplane technology. • The phase modulator is based on the fast-switching behaviour when operated in the symmetric H state of a nematic pi-cell. • Results are presented demonstrating the electric field conditions required to prolong the stability of the symmetric H state. • The experimental results are found to be in good agreement with results from simulations based upon Ericksen-Leslie continuum theory. In this paper, we investigate the optical phase modulation potential of a nematic liquid crystal (LC) pi-cell operating in the so-called symmetric H (Hs) state. Experimental results of the optical phase modulation obtained using a phase-shifting Michelson interferometer are presented which are then compared with results from simulations carried out using Ericksen-Leslie continuum theory. The stability of the Hs state, which is limited, is investigated by adjusting the amplitude of the applied voltage and the duration of the voltage burst. To achieve full 2π phase modulation with 1 ms timescale in a reflective geometry (akin to that of a spatial light modulator), we employ a short burst voltage to drive the LC pi-cell into the Hs state, which shows excellent phase modulation capability, and the experimental results are found to be in good agreement with the results from simulations. [ABSTRACT FROM AUTHOR]

• A novel technique for quantitative polarimetric evaluation of a spatial light modulator (SLM) using a compact and highly stable Sagnac interferometer. • Complete polarimetric analysis of SLM with varying gray values from 0 to 255. • Experimental demonstration of the proposed technique on the table-top and with external vibrations. • Highly stable and robust experimental geometry applicable even in external disturbances. A compact, stable and lens less digital holographic system is proposed and experimentally demonstrated for a polarimetric analysis of the spatial light modulator (SLM). The experimental design is implemented by using a robust cyclic shearing interferometer consisting of two mirrors and a beam splitter. A polarimetric response of the spatial light modulator with varying gray levels has been characterized by quantitatively extracting the complex fields of the orthogonal polarization components of the light emerging out of the reflective type SLM and results are presented. In order to examine stability of the proposed system, the experiment is performed on a table top and also in the presence of additional external vibrations. These results are compared with earlier results implemented by using a combination of Mach-Zehnder setup along with angular multiplexing of the reference fields. The obtained results indicate that the proposed technique is suitable even under external disturbances. The proposed technique is expected to be beneficial for the polarimetric imaging of objects and in the design of a stable digital holographic system. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we propose a holographic magnification system based on a cylindrical lens. The cylindrical lens has the function of converge and diverge beam only in the sagittal direction. The digital cylindrical lens consists of digital orthogonal cylindrical lenses on a spatial light modulator (SLM) and a solid cylindrical lens, and the vertical zoom in the holographic magnification system can quickly be controlled. The vertical magnification can be adjusted by tuning the focal length of the two digital cylindrical lenses. In order to illustrate the capabilities of the system, some experimental results are given. [ABSTRACT FROM AUTHOR]

We demonstrate a 2-channel orbital angular momentum (OAM) multiplexed free space optical communication (FSO) link using perfect optical vortex (POV) beams. POV beams are able to be transmitted coaxially over than 1m with the assistance of a microscope objective and normal lens. 16QAM-OFDM signals are used to measure the performance, which is also compared with the FSO link based on Laguerre–Gaussian (LG) vortex beams multiplexing in the same experimental environment. The results show that, the FSO link employing POVs multiplexing can bring a better performance to the system, which can always obtain a lower BER under the same received power; The using of POVs as carriers greatly reduces the systems’ sensitivity to the change of OAM topological charge numbers; And the constant diameter of POVs is also improve the versatility of the optical devices of different channels in the system. [ABSTRACT FROM AUTHOR]

Abstract The polarization state and beam shape of an ultrafast laser have been dynamically controlled using a spatial light modulator (SLM) with an additional S-waveplate (Altechena) for applications in material processing. Consequently, two different advanced states of polarization, radial and azimuthal, several star beam shapes were dynamically switched while synchronized with a motion control system. Imprinting laser induced plasmonic periodic surface structures(LIPSS) was employed to investigate the detailed vector fields at the image plane. The ablation footprint was found to match the selected beam shape and polarization states acurately. [ABSTRACT FROM AUTHOR]

Abstract A spatial light modulator (SLM) addressed with Computer Generated Holograms (CGH’s) can create structured light fields when an incident laser beam is diffracted by a phase CGH. The power handling limitations of SLMs based on a liquid crystal layer have always been of some concern. Now, with careful engineering of chip thermal management, we present the detailed optical phase and temperature response of a liquid cooled SLM exposed to picosecond laser average powers up to 220W at 1064nm – new knowledge critical for determining device performance at high laser powers. SLM chip temperature rose linearly with incident laser exposure, increasing by only 5°C at 220W incident power, measured with a thermal imaging camera. Thermal response time with continuous exposure was 1-2 seconds. The optical phase response with incident power approaches 2π radians with average powers up to 130W while above this power, liquid crystal thickness variations limit phase response to just over π radians. These remarkable performance characteristics show that liquid crystal based SLM technology is highly robust when efficiently cooled. High speed, multi-beam plasmonic surface micro-structuring at a coverage rate of 8cm2s-1 is achieved on polished metal surfaces at 25W exposure, while diffractive multi-beam surface ablation on stainless steel at an ablation rate of ∼4mm3min-1 is demonstrated with average power 100W. Continuous exposure for many hours exceeding 100W laser power did not result in any detectable drop in diffraction efficiency hence no permanent changes in SLM phase response characteristics have been observed This research work will help to accelerate the use of liquid crystal SLMs for both scientific and ultra-high throughput laser-materials micro-structuring applications. [ABSTRACT FROM AUTHOR]

Abstract Beam profile engineering where a desired optical intensity distribution can be generated by an array of phase shifting elements is a promising approach in laser material processing. Scalar Mathieu beams have elliptical intensity distribution perceivable as “optical knives” in the transverse plane. They exhibit non-diffracting properties similar to Bessel beams, where a relatively long focal depth retains unchanging intensity distribution, which makes Mathieu beams a promising approach in laser processing. Here, we introduce additionally vector Mathieu beams with controllable polarization and investigate numerically their spatial spectra. Further, we attempt to generate individual components of vector Mathieu beams experimentally using SLMs. We report on our achievements in the control over the beam shape and dimensions along the propagation axis. [ABSTRACT FROM AUTHOR]

Microscopy has been widely used to obtain three-dimensional images of a biological sample. However, it requires a scanning in axial direction and considerable time to acquire multiple depths information of a volumetric sample. In this paper, we demonstrate a method for single-shot multi-plane imaging based on programmable multiplexed grating patterns with no mechanical moving parts by using a digital micro-mirror device (DMD). The multiplexed grating pattern displayed on DMD, in a Fourier plane, splits light into separated beam paths and are able to compensate aberrations from the proposed system. In addition, resolution can be improved using an aberration-corrected multiplexed gratings pattern. We present and characterize the design, implementation, and experimentally demonstrate the proposed system’s ability through simultaneous multiple planes imaging of the biological samples. [ABSTRACT FROM AUTHOR]

Liquid-crystal spatial light modulator (SLM) is a widely-used adaptive device for beam shaping to achieve high quality nearfield measured by CCD camera in high power lasers. Precise image matching between the SLM and CCD is the key issue in this shaping system. We demonstrate an image matching method by using a four-blocker pattern written in the SLM and the output nearfield image measured by the CCD after long-distance spatial propagation. The size and edge-softening factor of the locating blocker in the SLM pattern is designed by using numerical simulation method. Experimental results show that when the locating blocker size is 1 mm and the edge-softening factor is 23%, a perfect CCD image can be achieved for matching with the SLM. [ABSTRACT FROM AUTHOR]

A high quality, dynamic laser beam shaping method is demonstrated by displaying a series of hybrid holograms onto a spatial light modulator (SLM), while each one of the holograms consists of a binary grating and a geometric mask. A diffraction effect around the shaped beam has been significantly reduced. Beam profiles of arbitrary shape, such as square, ring, triangle, pentagon and hexagon, can be conveniently obtained by loading the corresponding holograms on the SLM. The shaped beam can be reconstructed in the range of 0.5 mm at the image plane. Ablation on a polished stainless steel sample at the image plane are consistent with the beam shape at the diffraction near-field. The ±1st order and higher order beams can be completely removed when the grating period is smaller than 160 μm. The local energy ratio of the shaped beam observed by the CCD camera is up to 77.67%. Dynamic processing at 25 Hz using different shapes has also been achieved. [ABSTRACT FROM AUTHOR]

Holographic display is regarded as one of the most promising technologies to realize real three dimensional (3D) display in the near future. However, it is limited to low quality reconstruction and time consuming. In this paper, we present an effective design method of computer generated hologram (CGH), special constraints are introduced to control the signal to noise ratio (SNR) of the holographic image with high speed and accuracy, and high resolution of the holographic image to reduce speckles and granularsensation. Finally, simulation experiments are carried out to verify the performance of the proposed method. This work also can provide a feasible algorithm tool for holographic near-eye display in the field of augmented reality (AR) and virtual reality (VR). [ABSTRACT FROM AUTHOR]

Abstract Driven by their potential applications, vectorial optical fields with spatially inhomogeneous states of polarization within the cross section have drawn significant attention recently. This work intends to review some of the latest development of this rapidly growing field of optics and offer a general overview of the current status of this field in a few areas. Mathematical descriptions of generalized vectorial optical fields are provided along with several special examples. A time-reversal methodology for the creation of a wide variety of exotic optical focal fields with prescribed characteristics within the focal volume is presented. Recently developed methods for the generation of vectorial optical fields that utilize fiber lasers, digital lasers, vectorial optical field generator, metasurfaces or photoalignment liquid crystals are summarized. The interactions of these vectorial optical fields with various micro- and nano-structures are presented and the prospects of their potential applications are discussed. The connection of vectorial optical fields with higher dimensionality in quantum information is summarized. [ABSTRACT FROM AUTHOR]

Two-index Bessel beams (TIBBs) was introduced by Ornigotti and Aiello (2014) theoretically. In this paper, we propose a simple experimental scheme for generation of two-index Bessel–Gauss beams (TIBGBs), as an extension of the TIBBs. The scheme is based on manipulating the amplitude and phase in the Fourier plane with the use of a spatial light modulator and a spiral phase plate. Furthermore, we experimentally report the generation of the several examples of the TIBGBs based on the proposed optical system. The focusing properties of the TIBGB with indices p = 1 and l = 2 passing through a single lens are investigated both theoretically and experimentally. The experimental results agree well with theoretical predictions. [ABSTRACT FROM AUTHOR]

• A passive-detection-based WSPI method using a flexible SLM-based common-path interferometer is proposed. The common-path phase-shift or off-axis technique can be flexibly realized by a "sandwich" structure consisting of a half-wave plate, a SLM, and a polarizer. • The proposed method does not require sacrificing the pixel resolution of the SLM to introduce the reference light, therefore, there does not exist a tradeoff between the wavefront imaging resolution and field of view. • The proposed method for measuring wavefront as well as its application for quantitative phase imaging of a dragonfly wing was experimentally demonstrated, which indicates it has potential applications in the field of biological quantitative phase imaging. • The proposed method paves the way for passively measuring spatial wavefronts of unknown fields with higher performances, only using a single detector and the SLM-based "sandwich" structure, which is compact and simple. Wavefront single-pixel imaging (WSPI) is an important tool for simultaneously measuring the amplitude and phase of an unknown field, especially suitable for wavefront detecting in some special wavelengths where array detectors are immature or even unavailable. Here, a passive-detection-based WSPI method using a flexible SLM-based common-path interferometer is proposed, in which by detecting the zero-order diffraction of the SLM directly, the common-path phase-shift or off-axis technique can be flexibly realized by a "sandwich" structure consisting of a half-wave plate, a SLM, and a polarizer. The reference light can be conveniently chosen as the direct reflected light from the SLM, the unmodulated light from the pixels of the SLM, or the light from both of them. We experimentally verify the feasibility and advantages of the proposed method. We further demonstrate the method for wavefront measurement of a dragonfly wing, which suggests it can be used for quantitative phase imaging. It provides a high-resolution spatial wavefront passive detection technique, with a compact, stable, and flexible setup, which has lots of applications involving three-dimensional imaging, aberration correction, digital holographic measurement, and digital microscopy. [ABSTRACT FROM AUTHOR]

Beam shaping has been widely used in laser processing. Compared with Bessel beam, Bessel-like beam has unique advantages of fabricating high-aspect-ratio holes due to its tunable and longer non-diffraction length. However, the theoretical and experimental optimization of Bessel-like beams for laser manufacture has remained to be investigated. In this paper, we established a theoretical model of the intensity distribution and peak energy density of the Bessel-like beams based on a simplified phase of arc axicon. It was found that the longer propagation length and the lower peak energy density of the Bessel-like beams, contributed to the longer ablation length and higher ablation precision in the silica glass. The ablation length of the optimized Bessel-like beams was at least 1.6 times longer than that of the Bessel beam, which furtherly improved the fabrication efficiency of microdrilling. • Bessel-like beams were generated by an arc axicon. • The intensity distribution and peak energy density of Bessel-like beams were investigated. • The optimized Bessel-like beams ablated longer length and higher precision in silica glass. • Through-microholes array showed considerable precision and uniformity. [ABSTRACT FROM AUTHOR]

Speckle noise suppression in off-axis lensless Fourier transform digital holography by laterally shifting of object is analyzed quantitatively. Speckle decorrelation is directly proportional to the object displacement therefore object is shifted by three different amounts to test its effect on the speckle contrast reduction that is pixel size of camera, averaged speckle size and resolution pixel size of reconstruction plane. Phase-only spatial light modulator (LCOS) is used in object beam path to introduce the lateral shift in its position digitally without mechanical efforts by displaying a grating function. In comparison with the typical methods, the externally input lateral position shifts of object are controlled accurately, which makes the system effective and practicable. Averaged reconstructed results for three quantitative object lateral position shifts are compared and it has been found that the object shift by resolution pixel size of reconstruction plane shows better speckle contrast reduction and is in good agreement with the theoretical prediction. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a free-space optical communication link using perfect vortex beams. Perfect vortex beams with different topological charges are generated using a phase-modulation-type spatial light modulator (SLM) loaded with novel phase holograms based on the Bessel function. With the help of a microscope objective and simple lens, perfect vortex beams are transmitted effectively for a certain distance. After completing the demodulation of perfect vortex beams carrying OFDM 16-QAM signals and a series of offline processing on the Gaussian bright spot demodulated from the perfect vortex beams, we also achieve a communication link. The constellations and mean bit error rates (BER) of subcarriers are shown. [ABSTRACT FROM AUTHOR]

In laser projectors, speckle reduction can be achieved by projecting a changing binary phase diffuser onto the screen. Here, we sequentially encoded a commercialized ferroelectric liquid crystal spatial light modulator (FLC-SLM) with the rows of a two-level orthogonal array of order sixty-four, thus obtaining a changing binary phase diffuser. With the help of this binary phase diffuser, the subjective speckle contrast ratio on the screen is reduced from C b =0.71 to C a =0.1. Based on the experimental results, a simplified transparent FLC-SLM design is first proposed. This newly designed FLC-SLM has two phase modulation depths and can be driven with the passive matrix addressing scheme. Therefore, the control electronics of the proposed FLC-SLM can be significantly simplified compared to the currently used one. [ABSTRACT FROM AUTHOR]

We report on a study into multi-location laser ignition (LI) with a Spatial Light Modulator (SLM), to improve the performance of a single cylinder automotive gasoline engine. Three questions are addressed: i/ How to deliver a multi-beam diffracted pattern into an engine cylinder, through a small opening, while avoiding clipping? ii/ How much incident energy can a SLM handle (optical damage threshold) and how many simultaneous beam foci could thus be created? ; iii/ Would the multi-location sparks created be sufficiently intense and stable to ignite an engine and, if so, what would be their effect on engine performance compared to single-location LI? Answers to these questions were determined as follows. Multi-beam diffracted patterns were created by applying computer generated holograms (CGHs) to the SLM. An optical system for the SLM was developed via modelling in ZEMAX, to cleanly deliver the multi-beam patterns into the combustion chamber without clipping. Optical damage experiments were carried out on Liquid Crystal on Silicon (LCoS) samples provided by the SLM manufacturer and the maximum safe pulse energy to avoid SLM damage found to be 60 mJ. Working within this limit, analysis of the multi-location laser induced sparks showed that diffracting into three identical beams gave slightly insufficient energy to guarantee 100% sparking, so subsequent engine experiments used 2 equal energy beams laterally spaced by 4 mm. The results showed that dual-location LI gave more stable combustion and higher engine power output than single-location LI, for increasingly lean air-fuel mixtures. The paper concludes by a discussion of how these results may be exploited. [ABSTRACT FROM AUTHOR]