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Significance: The feedback-based wavefront shaping emerges as a promising method for deep tissue microscopy, energy control in bio-incubation, and re-configurable structural illuminations. The cost function plays a crucial role in the feedback-based wavefront optimization for focusing light through scattering media. However, popularly used cost functions, such as intensity ( η ) and peak-to-background ratio (PBR) struggle to achieve precise intensity control and uniformity across the focus spot., Aim: We have proposed an ℓ 2 -norm-based quadratic cost function (QCF) for establishing both intensity and position correlations between image pixels, which helps to advance the focusing light through scattering media, such as biological tissue and ground glass diffusers., Approach: The proposed cost function has been integrated into the genetic algorithm, establishing pixel-to-pixel correlations that enable precise and controlled contrast optimization, while maintaining uniformity across the focus spot and effectively suppressing the background intensity., Results: We have conducted both simulations and experiments using the proposed QCF, comparing its performance with the commonly used η and PBR-based cost functions. The results evidently indicate that the QCF achieves superior performance in terms of precise intensity control, uniformity, and background intensity suppression. By contrast, both the η and PBR cost functions exhibit uncontrolled intensity gain compared with the proposed QCF., Conclusions: The proposed QCF is most suitable for applications requiring precise intensity control at the focus spot, better uniformity, and effective background intensity suppression. This method holds significant promise for applications where intensity control is critical, such as photolithography, photothermal treatments, dosimetry, and energy modulation within and outside bio-incubation systems., (© 2024 The Authors.)

Selective laser etching is a promising candidate for the mass production of glass interposers. It comprises two steps: local modification by an ultrashort-pulsed laser and chemical etching of the modified volume. According to previous studies, when an ultrashort-pulsed laser beam is irradiated on the sample, electron excitation occurs, followed by phonon vibration. In general, the electron excitation occurs for less than a few tens of picoseconds and phonon vibration occurs for more than 100 picoseconds. Thus, in order to compare the electric absorption and thermal absorption of photons in the commercial glass, we attempt to implement an additional laser pulse of 213 ps and 10 ns after the first pulse. The modified glass sample is etched with 8 mol/L KOH solution with 110 °C to verify the effect. Here, we found that the electric absorption of photons is more effective than the thermal absorption of them. We can claim that this result helps to enhance the process speed of TGV generation.

Vectorial optical fields have garnered significant attention due to their potential applications in areas such as optical nano-fabrication, optical micromachining, quantum information processing, optical imaging, and so on. Traditional compact vectorial optical generators with amplitude modulation perform poorly in terms of diffraction effect reduction. To tackle this problem, the refractive 4f system in amplitude modulation is longitudinally aligned using an optimization approach presented in this research. The phase images used for longitudinal alignment are loaded into the liquid crystal spatial light modulator (SLM), and the distance between the lens and the mirror in the reflective 4f system is adjusted for longitudinal alignment by compensating for the neglected phase in the integrated module for the compact vectorial optical-field generator. The spot images collected by the CCD are processed using the improved eight-direction Sobel operator and Roberts function, and the longitudinal alignment in the reflective 4f system is determined by the sharpness of the image. The sharpness of the edges of the lines and the overall image are both enhanced after optimization compared to before optimization. The results demonstrate that the proposed method can effectively reduce the longitudinal alignment error of the reflective 4f system in the amplitude modulation of the compact vectorial optical-field generator, lessen the diffraction effect, and improve the performance of the system.

Hydrotherapy is a traditional clinical practice that has been widely used for pain relief. However, immersion in hot water influences skin's moisture and morphology. In this study, we investigate the physiological changes of ex‐vivo chicken skin immersed in hot water (at 40 and 50°C) via monitoring the change in its absorption and scattering properties using the spatial frequency domain imaging (SFDI) technique. The procedure started by calculating the modulation transfer function of the proposed imaging system over a range of spatial frequencies using a high‐resolution test target. Thereafter, structured illumination patterns at different spatial frequencies were projected onto the examined samples via a reflective phase‐only spatial light modulator using transmission and reflection modes. The transmission and reflection images were recorded using a digital camera to reconstruct the optical absorption and scattering parameters. Such parameters were calculated using Kubelka–Munk and lookup table methods. For system validation, the optical properties of two kinds of milk (skimmed and full cream), as reference samples, were reconstructed using the proposed SFDI system in the reflection mode via lookup table method. The results revealed an increase in the scattering coefficient of the skin samples immersed in higher water temperature, while the absorption coefficient values were nearly the same. Furthermore, the obtained results were validated using Monte‐Carlo method showing absolute errors that range from 0.004 to 0.057. In conclusion, the proposed system was presented to investigate the changes in ex‐vivo skin properties under thermal‐hydrotherapy in the context of measured changes in optical parameters. [ABSTRACT FROM AUTHOR]

Flattop beams are in high demand for a variety of applications, including uniform surface treatment, interference laser processing, repairing and skin therapy. In this experiment, we optimized the direction of phase grating to spatially separate the beam into extracted and residual components in the Fourier plane, and spatially filtered the components to form a square or hexagonal flattop beam with no wave‐like structure inside and high edge steepness. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There is a lot of interest in technology that controls the phase of light two dimensionally, such as laser waveform shaping and optical phase compensation. And a spatial light modulator is highly desired for practical use of these technologies. We have developed several types of spatial light modulators for years. The history of our research and development of spatial light modulators is shown here. [ABSTRACT FROM AUTHOR]

Spatial light modulators (SLMs) are versatile devices used for optical studies. These instruments have a wide area of application in photonics. Additionally, SLMs have potential utility in different applications, such as biomedical applications, laser based surgery for precise cutting and as optical tweezers to separate cells in a petri container. However, the high cost of SLM devices prevents their widespread use in many areas, including industrial areas and scientific research laboratories. This paper demonstrates how to design a digital light processor (DLP) based low-cost SLM and describes how to obtain structured electromagnetic waves with the designed SLM. Therefore, this research was undertaken to design and produce a low-cost SLM device for optical applications. For this purpose, two prerequisites had to be fulfilled, the first was to use suitable components of a projection device with DLP-based digital micro-mirror device (DMD), and the second was to eliminate unnecessary SLM components from the system. Finally, holographic images reflected on the SLM screen were created by using Mathematica software program to change the amplitude and phase of the electromagnetic waves in order to obtain the structured electromagnetic waves. [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]

Scaling the average power of ultrafast lasers into the kW range for high-throughput surface structuring and micromachining by the pulse energy requires an adapted processing strategy in order to minimize surface defects due to high fluences and maintain a high surface quality. One promising approach to distribute the pulse energy uniformly on the sample surface is spatial beam shaping using a spatial light modulator. The local phase was modulated by computer-generated holograms for the generation of uniform intensity distributions in the focal plane. The corresponding intensity distributions resulting from the different holograms were monitored with an on-axis camera to ensure accurate beam shapes during surface structuring and micromachining of the two materials stainless steel and cemented tungsten carbide. Uniform surface structures and flexible, dimensionally accurate cavities were machined with a shaped ultrafast laser beam and high pulse energies up to over 1 mJ on the sample surface. Various beam shapes with a cross-sectional area up to 0.42 mm² were generated on the sample surface for energy-efficient micromachining and homogenous surface structuring. The capability of high-energy pulse beam shaping was demonstrated by the fabrication of a large-area checkerboard pattern with small transition zones <10 µm between unprocessed and structured areas. [ABSTRACT FROM AUTHOR]

All optical approaches to control and read out the electrical activity in a cardiac syncytium can improve our understanding of cardiac electrophysiology. Here, we demonstrate optogenetic stimulation of cardiomyocytes with high spatial precision using light foci generated with a ferroelectric spatial light modulator. Computer generated holograms binarized by bidirectional error diffusion create multiple foci with more even intensity distribution compared with thresholding approach. We evoke the electrical activity of cardiac HL1 cells expressing the channelrhodopsin‐2 variant, ChR2(H134R) using single and multiple light foci and at the same time visualize the action potential using a calcium sensitive indicator called Cal‐630. We show that localized regions in the cardiac monolayer can be stimulated enabling us to initiate signal propagation from a precise location. Furthermore, we demonstrate that probing the cardiac cells with multiple light foci enhances the excitability of the cardiac network. This approach opens new applications in manipulating and visualizing the electrical activity in a cardiac syncytium. [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]

The combination of computer‐generated holography (CGH) and deep learning has opened the possibility to generate both realtime and high‐quality holograms. However, the widely‐used data‐driven deep learning method faces the limitation of the labeled training datasets. To address the above challenges, we propose model‐driven neural networks for high‐fidelity and high‐speed phase‐only hologram (POH) generation. The Fresnel diffraction model is introduced as the constraint to train the networks. Furthermore, the improvements of the network architecture and diffraction model effectively improve the reconstruction quality. High‐fidelity full‐color optical reconstructions of the 4K holograms have been achieved. [ABSTRACT FROM AUTHOR]

We have proposed and demonstrated a scalable and efficient scheme for programmable unitary operations in orbital angular momentum (OAM) domain. Based on matrix decomposition into diagonal and Fourier factors, arbitrary matrix operators can be implemented only by diagonal matrices alternately acting on orbital angular momentum domain and azimuthal angle domain, which are linked by Fourier transform. With numerical simulations, unitary matrices with dimensionality of 3×3 are designed and discussed for OAM domain. Meanwhile, the parallelism of our proposed scheme is also presented with two 3×3 matrices. Furthermore, as an alternative to verify our proposal, proof of principle experiments have been performed on path domain with the same matrix decomposition method, in which an average fidelity of 0.97 is evaluated through 80 experimental results with dimensionality of 3×3.

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]

It is very important for holographic optical tweezers (OTs) to develop high-quality phase holograms through calculation by using some computer algorithms, and one of the most commonly used algorithms is the Gerchberg–Saxton (GS) algorithm. An improved GS algorithm is proposed in the paper to further enhance the capacities of holographic OTs, which can improve the calculation efficiencies compared with the traditional GS algorithm. The basic principle of the improved GS algorithm is first introduced, and then theoretical and experimental results are presented. A holographic OT is built by using a spatial light modulator (SLM), and the desired phase that is calculated by the improved GS algorithm is loaded onto the SLM to obtain expected optical traps. For the same sum of squares due to error SSE and fitting coefficient η, the iterative number from using the improved GS algorithm is smaller than that from using traditional GS algorithm, and the iteration speed is faster about 27%. Multi-particle trapping is first achieved, and dynamic multiple-particle rotation is further demonstrated, in which multiple changing hologram images are obtained continuously through the improved GS algorithm. The manipulation speed is faster than that from using the traditional GS algorithm. The iterative speed can be further improved if the computer capacities are further optimized.

Reconstruction of 3D scenes from digital holograms is an important task in different areas of science, such as biology, medicine, ecology, etc. A lot of parameters, such as the object’s shape, number, position, rate and density, can be extracted. However, reconstruction of off-axis and especially inline holograms can be challenging due to the presence of optical noise, zero-order image and twin image. We have used a deep-multibranch neural network model, which we call HoloForkNet, to reconstruct different 2D sections of a 3D scene from a single inline hologram. This paper describes the proposed method and analyzes its performance for different types of objects. Both computer-generated and optically registered digital holograms with resolutions up to 2048 × 2048 pixels were reconstructed. High-quality image reconstruction for scenes consisting of up to eight planes was achieved. The average structural similarity index (SSIM) for 3D test scenes with eight object planes was 0.94. The HoloForkNet can be used to reconstruct 3D scenes consisting of micro- and macro-objects.

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]

Multi-focal laser direct writing (LDW) based on phase-only spatial light modulation (SLM) can realize flexible and parallel nanofabrication with high-throughput potential. In this investigation, a novel approach of combining two-photon absorption, SLM, and vector path-guided by scalable vector graphics (SVGs), termed SVG-guided SLM LDW, was developed and preliminarily tested for fast, flexible, and parallel nanofabrication. Three laser focuses were independently controlled with different paths, which were optimized according to the SVG to improve fabrication and promote time efficiency. The minimum structure width could be as low as 81 nm. Accompanied by a translation stage, a carp structure of 18.10 μm × 24.56 μm was fabricated. This method shows the possibility of developing LDW techniques toward fully electrical systems, and provides a potential way to efficiently engrave complex structures on nanoscales.

We present an array-based volume holographic optical element (vHOE) recorded as an optical combiner for novel display applications such as smart glasses. The vHOE performs multiple, complex optical functions in the form of large off-axis to on-axis wave front transformations and an extended eye box implemented in the form of two distinct vertex points with red and green chromatic functions. The holographic combiner is fabricated by our extended immersion-based wave front printing setup, which provides extensive prototyping capabilities due to independent wave front modulation and large possible off-axis recording angles, enabling vHOEs in reflection with a wide range of different recording configurations. The presented vHOE is build up as an array of sub-holograms, where each element is recorded with individual optical functions. We introduce a design and fabrication method to combine two angular and two spectral functions in the volume grating of individual sub-holograms, demonstrating complex holographic elements with four multiplexed optical functions comprised in a single layer of photopolymer film. The introduced design and fabrication process allows the precise tuning of the vHOE's diffractive properties to achieve well-balanced diffraction efficiencies and angular distributions between individual multiplexed functions. [ABSTRACT FROM AUTHOR]

Optical cryptosystems mostly use spatial distributions of amplitude, phase, and polarization of light to encrypt two-dimensional data/image. In this letter, we demonstrate the use of light carrying an array of optical vortices for image encryption. Spatially concatenated orthogonal states of optical vortices allow high-dimensional encoding and minimize the quality degradation during practical implementation. These features offer an efficient way to design an optical cryptosystem. [ABSTRACT FROM AUTHOR]

The rarely considered case of laser beam propagation and focusaing through the moderately scattering medium was researched. A phase-only spatial light modulator (SLM) with 1920×1080 pixel resolution was used to increase the efficiency of focusing of laser radiation propagated through the 5 mm layer of the scattering suspension of 1 µm polystyrene microbeads in distilled water with the concentration values ranging from 105 to 106 mm−3. A CCD camera with micro-objective was used to estimate the intensity distribution of the far-field focal spot. A Shack-Hartmann sensor was used to measure wavefront distortions. The conducted experimental research demonstrated the 8% increase in integral intensity and 16% decrease in diameter of the far-field focal spot due to the use of the SLM for laser beam focusing. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In two-photon microscopy, aberration correction is an essential technique for realizing high resolution in deep regions. A spatial light modulator (SLM) incorporated into an optical system for two-photon microscopy performs pre-compensation on the wavefront of the excitation beam, restoring the resolution close to the diffraction limit even in the deep region of a biological sample. If a spatial resolution smaller than the diffraction limit can be achieved along with aberration correction, the importance of two-photon microscopy for deep region observation will increase further. In this study, we realize higher resolution observations in the deep region by combining two resolution-enhancement methods and an aberration correction method. Therefore, a z-polarizer is added to the aberration-correction optical system, and the SLM modulates the amplitude and phase of the excitation beam; in other words, complex-amplitude modulation is performed. The lateral resolution is found to be approximately 20% higher than the diffraction limit obtained using a circularly polarized beam. Verification was conducted by simulation and experimentation using model samples and ex vivo biological samples. The proposed method has the potential to be effective for live imaging and photostimulation of the deep region of the sample, although it requires only minor changes to the conventional optical system that performs aberration correction. [ABSTRACT FROM AUTHOR]

Spatial light modulators (SLMs) exhibit a powerful capability of controlling electromagnetic waves. They are found to have numerous applications at terahertz (THz) frequencies, including wireless communication, digital holography, and compressive imaging. However, the development toward large‐scale, multi‐level, and multi‐functional THz SLM encounters technical challenges. Here, an electrically programmable THz metamaterial consisting of an array of 8×8 pixels is presented, in which the phase change material of vanadium dioxide (VO2) is embedded. After successfully suppressing the crosstalk from adjacent pixels, the THz wave can be modulated in a programmable manner. The switching speed of each pixel is in the order of 1 kHz. In particular, utilizing the hysteresis effect of VO2, the memory effect is demonstrated. The THz amplitude of each pixel can be written and erased by individual current pulses. Furthermore, multi‐state THz images can be generated and stored. This programmable metamaterial with memory function can be extended to other frequency bands and opens a route for electromagnetic information processing. [ABSTRACT FROM AUTHOR]

We propose a novel strategy for optical trapping and sorting of micro-nano particles that does not involve the flow of the immersion medium. The method employs the size- and velocity-dependent response of suspended polystyrene particles to the optical sieve of a dynamic fringelike pattern generated by a spatial light modulator. We not only experimentally demonstrate the trapping and transport of polystyrene particles with 2 μm diameter, but also study the sorting of a polydisperse suspension of polystyrene beads with diameters of 0.8 and 2 μm. The results provide new insights into particle manipulation and separation, and reveal that there is still scope for sorting smaller particles based on dynamic optical sieve. [ABSTRACT FROM AUTHOR]

A novel design of optical wavelength switch, based on an asymmetric switching architecture for edge node implementation, is presented in this paper. Compared to previous research for optical core transport network applications, the proposed work has a unique aspect to build dynamic multicasting and spectral equalization, vital functionalities for optical wavelength switch in the edge of optical access networks. An optical wavelength switch was experimentally implemented and evaluated in a 4 × 16 switching architecture to demonstrate the concept. This dynamic multicasting and spectral equalization were achieved by utilizing liquid crystal on a silicon spatial light modulator (LCoS-SLM) device. An optimal design of computer-generated holograms (CGHs) through an improved GS algorithm was used to perform the beam steering and wavelength switching. A variety of wavelength switching scenarios has been experimentally evaluated. The measurement results showed an average insertion loss of around −12.5 dB, and the calculated crosstalks were all less than −28 dB. Its applications in digital data transmissions were evaluated to achieve a transmission speed larger than 2.5 Gbps. The eye diagram measurement results showed that most wavelength switching scenarios have nearly bit-error-free transmission. The scenario includes the multicasting with spectral equalization within the proposed asymmetrical switching architecture.

The perfect optical vortex has successfully aroused substantial interest from researchers for its central dark hollow caused by spatial phase singularity in recent years. However, the traditional methods of combining the axicon and helical phase to generate the perfect optical vortex lead to an additional focus deviation in the tightly focused systems. Here, we report a multi-foci integration (MFI) method to produce the perfect optical vortex by accumulating a finite number of foci in the focal plane to overcome the additional focus deviation. Furthermore, based on MFI, we superposed two perfect optical vortices to obtain the spot array with controllable phase distribution and the number of spots. This work deepens our knowledge about superposed vortices and facilitates new potential applications. The micromanipulated experimental results agree well with our theoretical simulation. The spot array field provides new opportunities in direct laser writing, optical tweezers, optical communications, and optical storage.

Aberrations in the optical components and misalignments in the optical system cause a background phase in the coherent illumination. To reconstruct the object phase, the background phase illuminating the object must be measured and subtracted. For diffraction imaging and in-line holography, the traditional phase retrieval method reconstructs the phase diffracting from clear edges. However, it falls into stagnation when solving a background phase slowly varying in the spatial domain. In this study, we propose to solve the background phase using a modulation-based phase retrieval method. Alternative structured phase modulation (ASPM) can be the phase constraint to avoid stagnation when solving the background phase without clear edges. With ASPM, the background phase in the experiment can be efficiently retrieved when 16 phase patterns are employed. The ASPM acts as a phase grating to concentrate the intensities and provides robustness to noise. Compared to the conventional random phase modulations, the ASPM method had a smaller error value in the reconstruction iterations, which leads to a better reconstruction quality. After measuring and subtracting the background phase, the object phase was retrieved using a coherent diffraction imaging system. A phase plate can be accurately reconstructed under three different background phases.

In two-photon microscopy, aberration correction is an essential technique for realizing high resolution in deep regions. A spatial light modulator (SLM) incorporated into an optical system for two-photon microscopy performs pre-compensation on the wavefront of the excitation beam, restoring the resolution close to the diffraction limit even in the deep region of a biological sample. If a spatial resolution smaller than the diffraction limit can be achieved along with aberration correction, the importance of two-photon microscopy for deep region observation will increase further. In this study, we realize higher resolution observations in the deep region by combining two resolution-enhancement methods and an aberration correction method. Therefore, a z-polarizer is added to the aberration-correction optical system, and the SLM modulates the amplitude and phase of the excitation beam; in other words, complex-amplitude modulation is performed. The lateral resolution is found to be approximately 20% higher than the diffraction limit obtained using a circularly polarized beam. Verification was conducted by simulation and experimentation using model samples and ex vivo biological samples. The proposed method has the potential to be effective for live imaging and photostimulation of the deep region of the sample, although it requires only minor changes to the conventional optical system that performs aberration correction.

Jones–Stokes polarimetry is a robust in vitro polarimetric technique that can be used to investigate the anisotropic properties of a birefringent medium. The study of spatially resolved Jones matrix components of an object is a heuristic approach to extract its phase and polarization information. However, direct interpretation of Jones matrix elements and their decomposition into associated anisotropic properties of a sample is still a challenging research problem that needs to be investigated. In this paper, we experimentally demonstrate combined Jones–Stokes polarimetry to investigate the amplitude, phase, and polarization modulation characteristics of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). The anisotropic response of the SLM is calibrated for its entire grayscale range. We determine the inevitable anisotropic properties viz., diattenuation, retardance, isotropic absorption, birefringence, and dichroism, which are retrieved from the measured Jones matrices of the SLM using Jones polar decomposition and a novel algebraic approach for Jones matrix decomposition. The results of this study provide a complete polarimetric calibration of the SLM within the framework of its anisotropic characteristics. [ABSTRACT FROM AUTHOR]

The necessity of the correction of errors emerging during the optical encryption process led to the extensive use of data containers such as QR codes. However, due to specifics of optical encryption, QR codes are not very well suited for the task, which results in low error correction capabilities in optical experiments mainly due to easily breakable QR code's service elements and byte data structure. In this paper, we present optical implementation of information optical encryption system utilizing new multilevel customizable digital data containers with high data density. The results of optical experiments demonstrate efficient error correction capabilities of the new data container. [ABSTRACT FROM AUTHOR]

An optical system for converting linearly polarized laser beams into cylindrical vector beams is developed and experimentally investigated. The scheme is based on the coherent addition of mode beams using a Mach-Zehnder interferometer. The simplicity and versatility of the optical setup is achieved through the use of different sections in the area of the spatial light modulator for the si-multaneous generation of two spatially separated given mode beams. Each of the beams then propagates in one of the arms of the interferometer and undergoes the necessary polarization-phase transformations to obtain a cylindrical vector beam after the addition of mode beams.

We present an approach for engineering the intensity trajectory and phase gradient of light beams with arbitrary shapes by estimating their parametric equations using Freeman chain code and by applying the fast Fourier transform. The analysis of the electric field distribution expected for a given curve allows the phase extraction over each local coordinate, generating a phase pattern to be displayed over a spatial light modulator. The intensity and phase gradient of eight different shapes is encoded during our experiments. The far field intensity profiles are captured and compared in shape to those designed, while the encoded phase is demonstrated by implementing a common path interference setup with a pair of beams from the spatial light modulator. The designed beams, initially drawn either by hand or generated with software, exhibit both the intensity and phase profiles encoded onto them.

Holography is a prominent 3D display approach as it offers a realistic 3D display without the need for special glasses. Due to advancements in computation power and optoelectronic technology, holographic displays have emerged as widely appreciated technology among other 3D display technologies and have drawn a lot of research interest in recent years. The core of dynamic holographic displays is spatial light modulator (SLM) technology. However, owing to the limited resolution and large pixel size of SLMs, holographic displays suffer from certain bottlenecks such as limited field of view (FOV) and narrow viewing angle. To develop a holographic display at the commercial level, it is crucial to solve these problems. A variety of probable solutions to these challenges may be found in the literature. In this review, we discuss the essence of these approaches. We study the important milestones of the various methodologies from three primary perspectives—algorithms, optical systems, and devices employed for FOV extension—and provide useful insights for future research.

Achievements in the field of high-speed spatial modulation electrooptic components provide the possibility to create perspective optical-digital diffractive systems for information storage and processing that outperform modern electronic counterparts by utilizing throughput, energy efficiency, and reliability. This work presents a study of computer-generated holography methods that allow the formation of spatially-modulated information signals (data pages) with high accuracy using phase-only spatial light modulators. Computer-generated Fourier hologram fringe patterns were formed using bipolar intensity and double-phase coding. Numerical and experimental results of both methods’ implementation are compared. It was determined that bipolar intensity holograms provide higher data density on the data page if complex digital modulation methods such as multilevel amplitude and phase or quadrature modulation are used to represent data points. Double-phase coding can offer perspective for multilevel amplitude or multilevel intensity modulated data page reconstruction; however, exact control of phase modulation characteristics is required to obtain high reconstruction quality.

Compressive sensing (CS) has been proposed as a disruptive approach to developing a novel class of optical instrumentation used in diverse application domains. Thanks to sparsity as an inherent feature of many natural signals, CS allows for the acquisition of the signal in a very compact way, merging acquisition and compression in a single step and, furthermore, offering the capability of using a limited number of detector elements to obtain a reconstructed image with a larger number of pixels. Although the CS paradigm has already been applied in several application domains, from medical diagnostics to microscopy, studies related to space applications are very limited. In this paper, we present and discuss the instrumental concept, optical design, and performances of a CS imaging spectrometer for ultraviolet-visible (UV–Vis) stellar spectroscopy. The instrument—which is pixel-limited in the entire 300 nm–650 nm spectral range—features spectral sampling that ranges from 2.2 nm@300 nm to 22 nm@650 nm, with a total of 50 samples for each spectrum. For data reconstruction quality, the results showed good performance, measured by several quality metrics chosen from those recommended by CCSDS. The designed instrument can achieve compression ratios of 20 or higher without a significant loss of information. A pros and cons analysis of the CS approach is finally carried out, highlighting main differences with respect to a traditional system.

Nowadays, wavefront sensors are widely used to control the shape of the wavefront and detect aberrations of the complex field amplitude in various fields of physics. However, almost all of the existing wavefront sensors work only with quasi-monochromatic radiation. Some of the methods and approaches applied to work with polychromatic radiation impose certain restrictions. However, the contemporary methods of computer and digital holography allow implementing a holographic wavefront sensor that operates with polychromatic radiation. This paper presents a study related to the analysis and evaluation of the error in the operation of holographic wavefront sensors with such radiation.

Finding appropriate strategies to increase the robustness through turbulence with extended depth of focus (DOF) is a common requirement in developing high-resolution imaging through air or water media. However, conventional lenses with a specially designed structure require high manufacturing costs and are limited by a lack of dynamic modulation characteristics. Spatial light modulators (SLMs) are unique flat-panel optical devices which can overcome the distance limitation of beam propagation for the dynamic modulation property. In this work, we address the dynamic generation of a steady optical beam (STOB) based on the mechanism of transverse wave vector elimination. STOBs generated by the SLM have significant advantages over Gaussian beams for the characteristics of peak intensity, robust propagation, extended-DOF beam profile, and dynamic wavefront modulation over a long distance under strong turbulent media. Our versatile, extensible, and flexible method has promising application scenarios for the realization of turbulence-resistant circumstances.

Limited by the low space-bandwidth product of the spatial light modulator (SLM), it is difficult to realize multiview holographic three-dimensional (3D) display. To conquer the problem, a method based on the holographic optical element (HOE), which is regarded as a controlled light element, is proposed in the study. The SLM is employed to upload the synthetic phase-only hologram generated by the angular spectrum diffraction theory. Digital grating is introduced in the generation process of the hologram to achieve the splicing of the reconstructions and adjust the position of the reconstructions. The HOE fabricated by the computer-generated hologram printing can redirect the reconstructed images of multiview into multiple viewing zones. Thus, the modulation function of the HOE should be well-designed to avoid crosstalk between perspectives. The experimental results show that the proposed system can achieve multiview holographic augmented reality (AR) 3D display without crosstalk. The resolution of each perspective is 4K, which is higher than that of the existing multiview 3D display system.

A polarization‐independent liquid crystal (LC) device for large optical phase depth is demonstrated. Using LC layer with the twist angle of 180°, the parallel rubbing LC device shows good polarization‐independence. A phase modulator with a 180° twist LC layer and cell gap of 12um was fabricated whose polarization dependence can be lowered to 0.1% for 8.7π phase retardation at 532nm. The proposed LC phase modulator shows great potential for optical communication and imaging systems. [ABSTRACT FROM AUTHOR]

Silver nanowires (AgNWs) conductors with fine flexibility and high conductivity have been considered to have a promising perspective in the area of flexible transparent electrode. However, many challenges still exist in improving the conductivity of AgNWs films, such as high temperature and time‐consuming. Herein, an efficient and rapid method to weld AgNWs by spatial light modulated femtosecond (fs) laser is proposed. The Gaussian laser beam is modulated into a line‐shaped laser beam with the length of 773 μm. Compared with traditional spherical lens focus irradiation welding, the welding efficiency can be improved up to tens of times. The mechanism of fs laser welding is mainly to use high‐energy laser beam irradiation to generate local field enhancement which causes local high temperature at the nanowire junction. After laser welding, the sheet resistance of AgNWs films can be reduced to 14.7 Ω sq−1 at the transmittance of 89.5% without substrate damage. The welded AgNWs films exhibit excellent electrical conductivity even after 10 000 bending cycles. Moreover, the welded AgNWs films are used to make a flexible transparent heater, showing superior sheet resistance uniformity. [ABSTRACT FROM AUTHOR]