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Appropriate wavefront design can endow light fields with many useful properties, such as accelerating, anti‐diffracting, self‐healing, and the capability to exhibit customizable intensity shapes. The strategy of arbitrarily combining these properties to develop novel optical fields mainly relies on caustic methods. However, caustic methods have rarely been applied to the construction of vector fields. Here, slowly changing polarization information is introduced to the caustic rays, aiming to establish direct connections between conventional rays and vector beams in the physical representation. In this manner, a technique is developed to create non‐diffracting vector beams with polarization states that can vary along the caustic curves as needed. It is also demonstrated that the superposition of intersecting ray families can basically determine the polarization states of the other points in the fields. This may provide a new route for designing various novel vector fields and directly promote research in wave and focal field shaping, thereby offering more flexible beam options for applications such as material processing, particle manipulation, and microscopic imaging. [ABSTRACT FROM AUTHOR]

Surface textured materials can exhibit enhanced properties due to their unique morphology, large surface area, and modified surface properties. The laser etching process has garnered significant attention for its capability to create textures on sample surfaces, resulting in a substantial improvement of surface properties. In this study, we investigate the application of femtosecond laser etching on solid electrolytes. To achieve this, an axicon lens is employed to transform the conventional Gaussian beam into a Bessel beam, with an extended focal depth that facilitates the laser etching process. A telescope laser system with a Bessel beam having a focal length of 2 mm is constructed based on finite element analysis. Glassy LAGP [Li1.5Al0.5Ge1.5(PO4)3] with a thickness of 2 mm is successfully etched simultaneously on both surfaces using this approach. Utilization of femtosecond laser pulses effectively prevents sample melting during the process. As predicted by finite element analysis, wider ditches are observed on the surface compared to those on the backside due to higher laser intensity at the surface region. By modifying the parameters of the telescope laser system, size and depth control can be achieved for these ditches. [ABSTRACT FROM AUTHOR]

Laser‐powder bed fusion (L‐PBF) is extensively adopted in the aerospace and automobile industries for producing metallic components. The L‐PBF process involves rapid melting and solidification of metallic powders using a laser source to produce dense parts. Most industrial L‐PBF systems use a fiber‐based laser source that emits a Gaussian beam distribution. However, the conventional Gaussian beam used in L‐PBF processes presents inherent limitations that can impact the quality and properties of the final products. This review aims to provide a theoretical background of laser beam shaping techniques and explores the application of alternative beam shapes in L‐PBF. It investigates how different beam profiles affect the melt pool geometry, process stability, productivity, mechanical properties, microstructure, and surface roughness of fabricated parts. Additionally, it discusses different types of beam shaping techniques and elements utilized to generate distinct beam shapes. Furthermore, different constraints and limitations that hinder the full exploitation of beam shaping are critically discussed. By analyzing the impact of beam shaping in L‐PBF, this review provides insight into optimizing the additive manufacturing process, enhancing part quality, and improving processing performance. It will also help readers to overview the research gaps, challenges, and promising future directions in laser beam shaping applications in L‐PBF. [ABSTRACT FROM AUTHOR]

We describe a family of paraxial and quasi-monochromatic optical wave packets with finite energy and smoothly shaped amplitude in space and time that develops a singularity in the intensity when spatio-temporally focused by imparting a converging spherical wavefront and a negative temporal chirp. This singular behavior upon ideal focusing is manifested in actual focusing with finite apertures and in media with high-order dispersion with "exploding" behavior featuring an indefinitely increasing concentration of the energy when opening the aperture radius, thus exercising continuous control on the focal intensity and spatial and temporal resolution. These wave packets offer a new way of focusing that outperforms what can be achieved with standard Gaussian wave packets in terms of focal intensity and resolution, providing new possibilities in applications where energy concentration and its control are crucial. [ABSTRACT FROM AUTHOR]

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui 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.)

The simplicity and low-cost way to improve qualitative and quantitative analytical performance has always been a crucial concern for laser-induced breakdown spectroscopy (LIBS), and many scientists have been engaged in this evolving research direction. In this review, we investigated an update on recent developments in light-field modulated operation in LIBS. It covered a brief description of LIBS, optical polarization, and beam shaping. Here, the optical polarization is divided into laser beam polarization and plasma polarization. In addition, the methodology and development of light-field modulated LIBS were summarized and discussed. Finally, the existing problems with light-field modulated LIBS were presented, along with some of their own insights and the future direction of their development. This review will provide a guideline for LIBS researchers with basic knowledge, which is very useful in the signal optimization of LIBS research and applications. [ABSTRACT FROM AUTHOR]

THz radiation has gained great importance due to its potential applications in a wide variety of fields. For this reason, continuous efforts have been made to develop technological tools for use in this versatile band of the electromagnetic spectrum. Here, we propose a reflecting device with long focusing performances in the sub-THz band, using a bimirror device in which the relative angle is mechanically adjusted with the displacement of one of the mirrors. Despite the simplicity of the setup, the performance of this device is satisfactory down to a frequency of 0.1 THz. Theory and experience confirm that the bimirror is capable of focusing 0.1 THz radiation with a 2× magnification of the maximum input intensity while maintaining a longitudinal full width at half maximum (FWHM) of about 6 mm, which is about 12 times the depth of focus of a cylindrical optical element of the same focal length. In the absence of suitable THz equipment, the invariance property of the Fresnel diffraction integral allowed the predicted behavior to be tested in the THz range using conventional equipment operating at visible frequencies. [ABSTRACT FROM AUTHOR]

Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 µm. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features. [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.)

Terahertz radiation has emerged as a prominent solution for imaging and detection beyond visible and infrared. Active terahertz imaging is a widely used technology in this context especially for security applications and screening. Such systems are built around an illuminating source, a detecting module and a beam shaping system to match the detectors geometry. The overall system performance is largely dependent on an optimized choice of these modules. In this work, an active sub-terahertz scanning system working at 100 GHz frequency is proposed to detect concealed objects in parcels and mail. The system is optimized based on an adapted design of the beam shaper and a preprocessing correction of the images to ensure uniformity of response and cleanness. The proposed system demonstrated through experimentation improved resolution with a uniform response along its detection area. [ABSTRACT FROM AUTHOR]

Today, tailored laser beams are rarely used and thus an opportunity to optimize existing or introduce new processes is missed. New methods of dynamic beam shaping have the potential to change that in future. This keynote paper deals with methods allowing a transient energy input into the workpiece at such time scales that the underlying interaction processes are guided towards the desired result. It shows principles, categorizes necessary system technology, and gives application examples to familiarize the reader with the topic. It postulates that time-scale-dependent coupling between transient energy input and addressed process features is key for achieving the optimum. [ABSTRACT FROM AUTHOR]

In this study, we investigate the performance of axial-conical lenses, commonly referred to as Powell lenses, featuring varying fan angles of 5°, 7.5°, 10°, 15°, and 20°. Our objective is to evaluate their suitability for designing a light sheet generator tailored for fluorescence light-sheet microscopy of large samples. Our results indicate that Powell lenses with fan angles of 5° and 7.5° when integrated with additional aspheric components, exhibit optimal characteristics for this application. Specifically, employing a Powell lens with a 7.5° fan angle and 0.2 mm roundness at the tip facilitates the generation of a light sheet ideal for illuminating samples within a size range of 2,000 µm–15,000 µm. To validate the practicality of our optical design for real-world imaging tasks, we conducted imaging experiments on chicken embryos aged between 3 and 7 days. Our light-sheet microscopy system successfully captured intricate structural details, particularly highlighting the ongoing differentiation of the inner anatomy of these specimens. This approach has a high potential to improve the screening of pharmaceutical drugs acting on the vascularization of the chorioallantois membrane (CAM), a technique that is widely used in pharmaceutical research. [ABSTRACT FROM AUTHOR]

Collimated flat-top beam shapers primarily consisting of freeform lenses have a wide range of applications and pose challenges in terms of processing and integration when the diameter is less than millimeters. Metasurfaces represent a promising solution to planarize optics, can mimic any surface curvature without additional fabrication difficulty, and are suitable for flat-top optics. The conventional metasurface design approach relies on imparting the required phase using meta-atoms and encounters challenges in amplitude modulation due to near-field coupling and varying transmittances among meta-atoms with different phases, making the design of flat-top beam shapers difficult. In this paper, we propose a complex-amplitude constraint Gerchberg–Saxton algorithm for designing a collimated flat-top beam shaper metasurface doublet, which avoids the influence of strong near-field coupling on the amplitude distribution and simultaneously considers the amplitude-phase characteristics of the meta-atoms. A collimated flat-top beam with exceptional homogeneity Up of approximately 0.01, a wavefront error less than 0.1λ, and a transmittance higher than 86 % is experimentally obtained, comparable to commercial products based on freeform lenses. A collimated flat-top beam shaper metasurface doublet for generating flat-top beam is introduced, promoting efficient integration with laser systems. [ABSTRACT FROM AUTHOR]

Beam shaping is of significance for applications in various fields, including laser fusion, laser processing, and optical manipulation. One conventional approach for beam shaping is using the superposition of eigenmodes, such as the Hermite-Gaussian (HG) modes. However, despite the generation of a flat-top beam by HG modes with identical coefficients, it is challenging to achieve other specific intensity distributions by this method. In this study, we validate the feasibility of the beam patterns modulation by optimizing the coefficients of the superimposed modes using an optimization algorithm. Beyond producing square flat-top spots with controllable size and intensity, this method can also achieve specialized intensity distributions including hollow square spots.

In this paper, a planar reflectarray antenna is designed. The designed structure consists of new types of metamaterial unit cells. Two different flower-like shaped unit cells were studied at the center frequency of 12.5 GHz. The reflectarray contains multi cells with varying sizes of flowers. A metal plate and an air gap layer are placed behind the metamaterial sheet. A standard Ku band horn antenna feeds the structure. The F/D ratio is unity for the designed reflect array. Compared to previous reflectarray antennas, the designed reflect array consists of a limited number of cells, i.e. 121. Also, a new method without any try-and-error process is presented. The width of the designed reflector is so compact. This proposed method can be used for a reflectarray antenna with gain in the range of 20 to 30dBi with acceptable radiation efficiency. The CST software is performed to simulate and optimize the proposed structure. There is a good agreement between simulation and measurement results. [ABSTRACT FROM AUTHOR]

In recent years, laser technology has made significant advancements, yet there are specific requirements for the energy concentration and uniformity of lasers in various fields, such as optical communication, laser processing, 3D printing, etc. Beam shaping technology enables the transformation of ordinary Gaussian-distributed laser beams into square or circular flat-top uniform beams. Currently, LCOS-based beam shaping algorithms do not adequately meet these requirements, and most of these algorithms do not simultaneously consider the impact of phase quantization and zero-padding, leading to a decrease in the practicality of phase holograms. To address these issues, this paper proposes a novel segmented beam shaping algorithm that combines iterative and simulated annealing approaches. This paper validated the reliability of the proposed algorithm through numerical simulations. Compared to other algorithms, the proposed algorithm can effectively reduce the root mean square error by an average of nearly 37% and decrease the uniformity error by almost 39% without a significant decrease in diffraction efficiency. [ABSTRACT FROM AUTHOR]

In order to improve the uneven distribution of laser energy in laser-induced breakdown spectroscopy(LIBS) technology, simulation software was used to simulate the optical path imaging of flat convex cylindrical mirrors with different focal lengths of 12.5 mm radius. The simulation showed that the optimal focal length meeting the laser conditions was 100 mm. On this basis, a shaping system based on LIBS beam was built. Compared with the non-convex mirror, the mean square error coefficient of focal spot light intensity for the strontium element in the sample decreased by an average of 41.91%, the peak-to-valley ratio of focal spot intensity decreased by an average of 41.27%, the energy uniformity increased by an average of 17.23%, and the coefficient of determination for the fitting increased from 0.860 to 0.914. The results show that the plano-convex cylindrical mirror can improve the uniformity of beam energy, proving that it is an effective method for laser beam shaping. [ABSTRACT FROM AUTHOR]

Near-field bending of a laser diode bar (i.e., the SMILE effect) degrades the laser beam brightness, adversely affecting optical coupling and beam shaping. Previous reports mainly focused on the two-dimensional near-field bending of a laser diode bar. However, the near-field bending of a laser diode bar not only occurs in the laser bar growth direction, but also in the beam propagation direction. The present article proposes the three-dimensional near-field bending of a laser diode array, which is commonly known as the three-dimensional spatial SMILE effect. Through theoretical and simulated investigations, it has been found that a laser bar array not only deforms in the fast axis direction to cause the traditional two-dimensional SMILE effect but also experiences an additional deformation of approximately 2 μm in the laser emission direction simultaneously. Due to the SMILE effect in the beam propagation direction, not all emitters are aligned in a straight line, and some emitters experience defocusing during collimation. Consequently, there is an increase in the residual divergence angle and beam width, resulting in a degradation of the laser bar array's beam quality. According to the theoretical calculations, ZEMAX simulations, and experimental results, for a FAC (fast axis collimation) with a focal length of 300 μm, the divergence angle of single emitter after collimating in the fast axis increases from 4.95 mrad to 6.46 mrad when the offsetting of the working distance between the incident beam waist and FAC lens increases from 0 μm to 2 μm. [ABSTRACT FROM AUTHOR]

In recent years, the topic of beam shaping for improved laser material processing has rapidly grown influencing metal laser powder bed fusion (PBF-LB/M). Given the need to reduce the cost and improve control of the PBF-LB/M process to make it more competitive with traditional manufacturing methods, increasing productivity of PBF-LB/M is critical. When research reports a new beam profile (e.g. ring profile) to improve productivity on a specific material, it is often generalised, and assumed to have the capability to improve productivity in PBF-LB/M across the board. In this work, we use both low-fidelity simulations and experimental work to investigate the difference between Gaussian and ring/spot beam profiles on metals with very different thermal properties (a stainless steel and an aluminium alloy). We show that the two materials have opposite responses to the change in beam profile (both in terms of melt pool dimensions and thermal gradients); further, the most beneficial intensity distribution is dependent on the energy input to the material. This exemplifies yet another way in which the PBF-LB/M process is non-linear and contradicts the idea that a ring/spot laser profile is beneficial for all laser processing technologies. This highlights the need for further research into the non-linear effect of varying intensity distributions on laser processing before the benefits of dynamic beam shaping can be truly realised.

Abstract A simple numerical method is proposed for the design of two aspherical surfaces, each comprising multiple segmented refractive planes, for generating a collimated beam with a specific irradiance profile in a beam shaping system with a divergent light source. However, in real-world manufacturing, this performance improvement is obtained at the expense of a greater cost and complexity. Accordingly, a second algorithm is proposed which maximizes the number of rays passing through the central regions of the refractive planes in the second aspherical surface and hence minimizes the total number of segments required to achieve the same beam shaping performance. The feasibility of the proposed method is demonstrated through the design of two aspherical lenses for generating collimated output beams with ring- and triangle-like irradiance profiles, respectively. The experimental results show that the beam profiles are in close agreement with the desired irradiance distributions. In general, the results indicate that the proposed method provides a versatile and efficient approach for achieving the desired collimated profile in beam forming systems with a divergent light source.

We describe a family of paraxial and quasi-monochromatic optical wave packets with finite energy and smoothly shaped amplitude in space and time that develops a singularity in the intensity when spatio-temporally focused by imparting a converging spherical wavefront and a negative temporal chirp. This singular behavior upon ideal focusing is manifested in actual focusing with finite apertures and in media with high-order dispersion with “exploding” behavior featuring an indefinitely increasing concentration of the energy when opening the aperture radius, thus exercising continuous control on the focal intensity and spatial and temporal resolution. These wave packets offer a new way of focusing that outperforms what can be achieved with standard Gaussian wave packets in terms of focal intensity and resolution, providing new possibilities in applications where energy concentration and its control are crucial.

A simple numerical method is proposed for the design of two aspherical surfaces, each comprising multiple segmented refractive planes, for generating a collimated beam with a specific irradiance profile in a beam shaping system with a divergent light source. However, in real-world manufacturing, this performance improvement is obtained at the expense of a greater cost and complexity. Accordingly, a second algorithm is proposed which maximizes the number of rays passing through the central regions of the refractive planes in the second aspherical surface and hence minimizes the total number of segments required to achieve the same beam shaping performance. The feasibility of the proposed method is demonstrated through the design of two aspherical lenses for generating collimated output beams with ring- and triangle-like irradiance profiles, respectively. The experimental results show that the beam profiles are in close agreement with the desired irradiance distributions. In general, the results indicate that the proposed method provides a versatile and efficient approach for achieving the desired collimated profile in beam forming systems with a divergent light source. [ABSTRACT FROM AUTHOR]

Laser welding is a key enabling technology that transitions toward electric mobility, producing joints with elevated electrical and mechanical properties. In the production of battery packs, cells to busbar connections are challenging due to strict tolerances and zero-fault policy. Hence, it is of great interest to investigate how beam shaping techniques may be exploited to enhance the electromechanical properties as well as to improve material processability. Industrial laser systems often provide the possibility to oscillate dynamically the beam or redistribute the power in multicore fibers. Although contemporary equipment enables elevated flexibility in terms of power redistribution, further studies are required to indicate the most adequate solution for the production of high performance batteries. Within the present investigation, both in-source beam shaping and beam oscillation techniques have been exploited to perform 0.2–0.2 mm Ni-plated steel welds in lap joint configuration, representative of typical cell to busbar connections. An experimental campaign allowed us to define process feasibility conditions where partial penetration welds could be achieved by means of in-source beam shaping. Hence, beam oscillation was explored to perform the connections. In the subset of feasible conditions, the mechanical strength was determined via tensile tests alongside electrical resistance measurements. Linear welds with a Gaussian beam profile enabled joints with the highest productivity at constant electromechanical properties. Spatter formation due to keyhole instabilities could be avoided by redistributing the emission power via multicore fibers, while dynamic oscillation did not provide significant benefits. [ABSTRACT FROM AUTHOR]

Despite the maturity of laser-based powder bed fusion of metals (PBF-LB/M), some barriers prevent the manufacturing process from fully being established in the industry. One drawback is spatter formation, which is disadvantageous to PBF-LB/M for three main reasons. First, adhering spatter can initiate coater collision, resulting in process failure. Second, large adhering spatter may cause lack-of-fusion defects as they require more energy to remelt sufficiently compared to unprocessed powder. Furthermore, big nonadhering spatter cannot be recycled as powder. The recycling of small spatter particles potentially results in degraded material properties. Ring-shaped beam profiles have been established for deep penetration welding to reduce spatter formation. Investigations on ring-shaped beam profiles in PBF-LB/M focus on improving productivity and process robustness. Qualitative spatter reduction in PBF-LB/M using ring-shaped beam profiles has also been reported. This publication quantitatively examines the influence of ring-shaped beam profiles on spatter formation in PBF-LB/M. Image processing algorithms of on-axis high-speed images are utilized for spatter detection and tracking. A self-developed spatter segmentation is used to determine the spatter size. A Laplacian of Gaussian filter is combined with a Kalman tracker to count and track the spatter. The results show that spatter formation is highly influenced by the beam profile and the chosen process parameters. Considering the melt track width, ring-shaped beam profiles could reduce the number of spatter per fused area. High numbers of spatter are generated when parameter sets result in balling. Moreover, spatter velocity is primarily dependent on the introduced dimensionless enthalpy. [ABSTRACT FROM AUTHOR]

In the recent years, laser beam welding has become an established joining process, especially for components in the electrical powertrain (copper applications). However, laser beam welding of copper is generally considered to be difficult, particularly due to its high heat conductivity and due to its low absorptivity using laser sources with a wavelength of 1 μm. The resulting welds show numerous weld defects, such as pores and spatters. Using "blue" lasers with a wavelength of 450 nm promises a smoother welding process with less spatters. Therefore, a blue diode laser with increased absorptivity in copper materials was developed by Laserline and used for welding copper. In this contribution, the results of welding copper using blue lasers with respect to the penetration depth and the resulting weld quality are discussed. In addition, investigations by Bosch at the electron-synchrotron DESY with a blue diode laser enabled us to have a look into the material during welding. Consequently, melt pool dynamics and capillary dynamics were analyzed with respect to the formation of weld defects and will be discussed as well. Furthermore, it is demonstrated that it can be beneficial to use a so-called spot-in-spot beam shaping tool to further improve the melt pool dynamics and, therefore, the resulting weld quality. [ABSTRACT FROM AUTHOR]

The ever-increasing popularity of the terahertz (THz) frequency range reveals the increasingly obvious applicability limiting factor - the price of the final setup. This study is intended to contribute to the solution by evaluating the THz frequency range suitability of the optical components, fabricated using two easily accessible materials - high impact polystyrene (HIPS) and paraffin. The primary analysis using time-domain spectroscopy (TDS) revealed promising results, as both materials had sufficient refractive indexes of n ≈ 1.55 and a high transmittance. That allowed one to assume the feasibility of creating a low-cost THz frequency range lens. Lenses of focal lengths of f = 20, 30, 40 mm were fabricated using extrusion 3D printing and paraffin moulding. The produced lenses showcased the satisfactory beam focusing ability, comparable to that of already existing much less cost-efficient solutions. The THz imaging using the fabricated lenses has successfully been realized, proving the applicational possibilities of the imaging system with the proposed low-cost components employed. [ABSTRACT FROM AUTHOR]

Line-shaped beam-based Doppler distance sensors enable 3D shape measurements of rotating objects, for instance for working lathe monitoring with a simultaneous, multipoint velocity, and distance measurement. The velocity and distance estimations are fundamentally referred to the interference fringe spacing of the sensors. In this case, the fringe spacing variation-caused measurement error is significant; however, a complete, accurate model of the fringe geometry distribution for the line-shaped fringe volume is still missing and required to identify and minimize the error. Therefore, this work presents a high-accuracy 3D model for the fringe spacing evaluation of the sensors with experimental investigations. The model is derived from the phase expression of Gaussian beams introducing extension ratio, and can be universally applied to describe fringe geometry distribution throughout the intersection volume of spherical and line-shaped beams. With an experimental setup of a laser Doppler sensor, a full-field fringe spacing estimation using a high-resolution matrix camera is performed with dual-wavelength beams. The numerical modeling and experimental results show an average relative difference below 0.6 % . [ABSTRACT FROM AUTHOR]

Solidification cracking is a prevalent defect in welding aluminium alloys which can be effectively mitigated by employing grain refinement strategies. This paper investigates the feasibility of tailoring the weld zone grain structure of 6xxx series aluminium alloys using an adjustable ring mode (ARM) laser beam to reduce the centreline cracking susceptibility. An in-process monitoring approach, comprising a high-speed camera and an ad-hoc Digital Image Correlation, was adopted to examine the strain development during laser welding on a self-restraint test rig. Results revealed that transverse strain in the weld centre exhibits a parabola-like relationship with the core/ring power ratio, with the minimum strain determined at the power ratio of ∼1.5, regardless of the total power employed. The microstructural analysis demonstrated that increasing the core/ring power ratio can lead to the refinement of columnar and equiaxed grains. Furthermore, the formation of secondary equiaxed grains is promoted when the power ratio increases, and this is proved to be related to the characteristic of the ARM laser by the like-for-like comparison. Overall, a fine-tuned power ratio of 1.5 is determined in the studied material and welding configuration for achieving a centreline crack free weld, benefiting from the improved microstructure and reduced thermal strain.

Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 µm. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features.

THz radiation has gained great importance due to its potential applications in a wide variety of fields. For this reason, continuous efforts have been made to develop technological tools for use in this versatile band of the electromagnetic spectrum. Here, we propose a reflecting device with long focusing performances in the sub-THz band, using a bimirror device in which the relative angle is mechanically adjusted with the displacement of one of the mirrors. Despite the simplicity of the setup, the performance of this device is satisfactory down to a frequency of 0.1 THz. Theory and experience confirm that the bimirror is capable of focusing 0.1 THz radiation with a 2× magnification of the maximum input intensity while maintaining a longitudinal full width at half maximum (FWHM) of about 6 mm, which is about 12 times the depth of focus of a cylindrical optical element of the same focal length. In the absence of suitable THz equipment, the invariance property of the Fresnel diffraction integral allowed the predicted behavior to be tested in the THz range using conventional equipment operating at visible frequencies.

We demonstrate and compare two approaches for reducing processing time for ultrashort pulse laser surface functionalization with application to femtosecond laser hyperdoping of silicon with a laser pulse duration of 800 fs and an irradiation wavelength of 1030 nm. In the first, we use a Gaussian intensity distribution and increase the repetition rate from 1 kHz to 1002 kHz while keeping all other parameters and thus the accumulated fluence constant. We find that the sub-bandgap absorptance of the material, which we take as target measure, decreases above a repetition rate of 250 kHz. This suggests an inherent limitation of this approach. The second approach is characterized by the use of a line-shaped intensity distribution which is achieved by diffractive beam shaping using a phase-only spatial light modulator. This process proves to be suitable for laser hyperdoping of silicon with a 22-fold enhanced area processing rate while maintaining a sub-bandgap absorptance of above 80 %abs. [ABSTRACT FROM AUTHOR]

Fabricating precision microgrooves with controllable cross‐sections on difficult‐to‐machine materials is significantly valuable but still challenging. Herein, a patterned laser‐induced microjet‐assisted ablation method for cross‐sectional profiles controllable laser micromachining is proposed. During the liquid‐assisted laser ablation process, debris and bubbles that may disturb the laser energy deposition can be instantaneously expelled by a directional laser‐induced microjet. The Gaussian laser spot is spatially modulated into specific geometric shapes, such as triangles, to tune locally deposited laser energy to carve microgrooves with designed cross‐sections. To achieve customized microgrooves efficiently, a reliable geometrical model based on the ablation threshold theory is developed to guide the processing parameter selection, including the laser spot shape, polarization, pulse energy, and scanning strategies. The simulation and experimental results confirm that this method achieves the decoupled control of the groove depth and width in a single‐path laser ablation process. Using this method, the design and manufacturing of microgrooves with controllable cross‐sections on single crystalline silicon carbide are demonstrated. The patterned laser‐induced microjet‐assisted ablation method provides a new route for fabricating precision microgrooves with controllable cross‐sections on difficult‐to‐machine materials. [ABSTRACT FROM AUTHOR]

In this paper, a beam shaping-based method for design of optical imaging lens is proposed. The optical imaging lens is designed with Fresnel diffraction theory to focus light, and the focusing parameters of the lens, such as the number of the foci, the focal length, the size and the shape of the focal spot, and so on, can be set with great freedom. Therefore, the lens has great flexibility in optical imaging, and the imaging resolution can also be varied with the design. The optical imaging lenses possess advantages such as simple structure, compact size, customized imaging effect, and high performance. The proposed method can be extensively applied to the design of flat optical elements and the customized optical imaging. [ABSTRACT FROM AUTHOR]

This study seeks to characterize and modify some of the major parameters of blue-light diode lasers and indicate the significance of developing this field of technology. Our diode begins to work at the threshold current of 650 mA with the output wavelength of 463 nm. By designing an efficient cooling system, a current of 5.8 (even further) Amperes can pass safely through the diode at a voltage of 6.3 V., to produce a stable 3.5 Watts output power. With an optical arrangement for the shaping of the beam emitted from the diode, the M2 factor is decreased from the value of 11.27 × 2.34 before the beam shaping to the value of 1.38 × 1.59 after the beam shaping with the beam spot size of 240.30 × 232.45 μm2. The major parameters such as laser stability in time, voltage–current-power diagram, slope efficiency, external quantum efficiency, power conversion efficiency, and the polarization degree were also measured. [ABSTRACT FROM AUTHOR]

In this paper, a beam shaping scheme is presented for the optimal design of base station antenna array. The antenna array consists of four linearly arranged dual-band dual-polarized antenna elements, and it is designed to cover the LTE frequency band (2.3-2.69 GHz) and 5G frequency band (3.3-3.6 GHz). The shaped beams with possible maximum gain, suppressed sidelobe level smaller than −16 dB, front-to-back ratio larger than 18dB, and filled-up null point larger than −23 dB are accomplished through two steps by using the unconstrained methods of maximum power transmission efficiency (MMPET) and constrained MMPTE, respectively. In the proposed beam shaping scheme, all the realistic factors of the antenna array have been taken into account, such as the difference of element radiation patterns, complexity and tolerance of the element structure and spacing.

In recent years, laser technology has made significant advancements, yet there are specific requirements for the energy concentration and uniformity of lasers in various fields, such as optical communication, laser processing, 3D printing, etc. Beam shaping technology enables the transformation of ordinary Gaussian-distributed laser beams into square or circular flat-top uniform beams. Currently, LCOS-based beam shaping algorithms do not adequately meet these requirements, and most of these algorithms do not simultaneously consider the impact of phase quantization and zero-padding, leading to a decrease in the practicality of phase holograms. To address these issues, this paper proposes a novel segmented beam shaping algorithm that combines iterative and simulated annealing approaches. This paper validated the reliability of the proposed algorithm through numerical simulations. Compared to other algorithms, the proposed algorithm can effectively reduce the root mean square error by an average of nearly 37% and decrease the uniformity error by almost 39% without a significant decrease in diffraction efficiency.

Near-field bending of a laser diode bar (i.e., the SMILE effect) degrades the laser beam brightness, adversely affecting optical coupling and beam shaping. Previous reports mainly focused on the two-dimensional near-field bending of a laser diode bar. However, the near-field bending of a laser diode bar not only occurs in the laser bar growth direction, but also in the beam propagation direction. The present article proposes the three-dimensional near-field bending of a laser diode array, which is commonly known as the three-dimensional spatial SMILE effect. Through theoretical and simulated investigations, it has been found that a laser bar array not only deforms in the fast axis direction to cause the traditional two-dimensional SMILE effect but also experiences an additional deformation of approximately 2 μm in the laser emission direction simultaneously. Due to the SMILE effect in the beam propagation direction, not all emitters are aligned in a straight line, and some emitters experience defocusing during collimation. Consequently, there is an increase in the residual divergence angle and beam width, resulting in a degradation of the laser bar array’s beam quality. According to the theoretical calculations, ZEMAX simulations, and experimental results, for a FAC (fast axis collimation) with a focal length of 300 μm, the divergence angle of single emitter after collimating in the fast axis increases from 4.95 mrad to 6.46 mrad when the offsetting of the working distance between the incident beam waist and FAC lens increases from 0 μm to 2 μm.

Thanks to its unique optical sectioning capability, light-sheet fluorescence microscopy has proven to be a powerful technique for volumetric imaging of entire model organisms with high spatial and temporal resolution. For light sheet generation with scanned laser beams, holographic beam shaping offers precise control over the optical fields exciting the fluorescence. Various illumination schemes have been proposed, aiming for best image quality with regard to axial resolution, optical sectioning, illumination homogeneity and photobleaching while at the same time retaining a large field of view. Here, we have engineered and characterized a variety of beams and analyzed their imaging performance by using phantom samples and zebrafish embryos. These data may assist researchers to select the light sheet best suited to the imaging application at hand.

In ultra-high-power/energy solid-state Nd:glass laser facilities, the gain distribution of the main amplifier system (MAS) is nonuniform owing to strong amplified spontaneous emissions in the MAS. A shaped beam profile from a preamplifier (PreAMP) should be set opposite to the gain profile in the MAS to obtain a high-power beam with an approximately flat beam profile. This flat beam profile can result in the high efficiency of the frequency-conversion crystals. In this study, the laser beam was spatially formatted as an M-shaped beam with precompensation (PreCOM) for the nonuniform gain profile of the MSA. Modulation of the cross-sectional gain distribution of the PreAMP was demonstrated by selecting the absorption coefficient of the Nd:glass rod and pump configuration. Using the proposed off-axis relay-imaging eight-pass amplifier, an M-shaped beam with an output pulse energy of 1 J and a repetition rate of 1 Hz was experimentally achieved. With an Nd3+ concentration of 1.2 wt% and Nd: glass rod diameter of 18 mm, an M-shaped beam profile with a 4.3:1 ratio of intensity at the margin to that at the center was successfully obtained. Such controllable M-shaped beams can be optionally introduced to the MAS to compensate for non-uniform spatial gain profiles.

An iterative algorithm of high resolution is presented that resolves the complex local modulation problem of light fields by determining random phase-only masks. The algorithm is constructed from the discrimination of spatial frequencies of the target field. The relation between the maximum intensity values of the incident and target fields allows quantifying the level of accuracy accepted by the user. The advantages and disadvantages of this approach are shown and discussed. The high quality obtained in the random phase-only masks calculation suggests the implementation of double image encryption methods when the incident field possesses amplitude and phase random values. [ABSTRACT FROM AUTHOR]

The commonly used Gaussian intensity distribution during the laser-based processing of metals can negatively affect melt pool stability, which might lead to defects such as porosity, hot cracking, or poor surface quality. Hot cracking is a major factor in limiting production rates of high-strength aluminium alloys in laser-based processes such as welding or the powder bed fusion of metals (PBF-LB/M). Going away from a Gaussian intensity distribution to ring-shaped profiles allows for a more even heat distribution during processing, resulting in more stable melt pools and reduced defect formations. Therefore, the aim of this study is to investigate the influence of different laser beam profiles on the processing of high-strength aluminium alloys by using a multicore fiber laser, allowing for in-house beam shaping. Single weld tracks on the aluminium alloy EN AW-5083 are produced with varying laser powers and weld speeds, as well as different beam profiles, ranging from Gaussian intensity distribution to point/ring profiles. The molten cross sections are analyzed regarding their geometry and defects, and the surface roughness of the weld tracks is measured. By using point/ring beam profiles, the processing window can be significantly increased. Hot cracking is considerably reduced for weld speeds of up to 1000 mm/s compared to the Gaussian beam profile. Furthermore, the melt pool width and depth are more stable, with varying parameters for the point/ring profiles, while the Gaussian beam tends to keyhole formation at higher beam powers. Finally, a strong decrease in surface roughness for the point/ring profiles, accompanied by a significantly reduced humping effect, starting even at lower beam powers of 200 W, can be observed. Therefore, these results show the potential of beam shaping for further applications in laser-based processing of high-strength aluminium alloys. [ABSTRACT FROM AUTHOR]

Digital programmable coding metasurfaces (DPCMs) have recently attracted enormous attention and have been broadly applied, owing to their ability to manipulate electromagnetic (EM) wave behaviours and programmable multi-functionality. Recent DPCM works are divided into reflection and transmission types (R-DPCM and T-DPCM, respectively); however, there are only a few reported T-DPCM works in the millimetre-wave spectrum, owing to the difficulty of realising the large-phase controllable range while maintaining low transmission losses with electronic control components. Consequently, most millimetre-wave T-DPCMs are demonstrated only with limited functions in a single design. Additionally, all these designs use high-cost substrate materials that constrain practical applicability, owing to cost-ineffectiveness. Herein, we propose a 1-bit T-DPCM that simultaneously performs three dynamic beam-shaping functions with a single structure for millimetre-wave applications. The proposed structure is completely constructed using low-cost FR-4 materials, and operation of each meta-cell is manipulated using PIN-diodes, thus driving the achievement of multiple effective dynamic functionalities including dual-beam scanning, multi-beam shaping, and orbital-angular-momentum-mode generation. It should be noted that there are no reported millimetre-wave T-DPCMs demonstrating multi-function design, thus showing a gap in the recent literature of millimetre-wave T-DPCMs. Moreover, cost-effectiveness can be significantly enhanced, owing to the construction of the proposed T-DPCM using only low-cost material. [ABSTRACT FROM AUTHOR]

The shape of the laser beam used for fusion cutting significantly influences the geometry of both the cutting front and the cutting kerf. The angle of the cutting front in turn impacts the local absorptivity, while the width of the kerf defines the amount of material, which has to be molten. The kerf's geometry therefore determines the maximum possible cutting speed at which a successful cut is feasible with a given available laser power. The absorptivity, the width of the kerf, and the maximum possible cutting speed can be estimated from a simple model considering the conservation of energy and rough geometrical approximations. In order to verify the prediction of the model, the geometry of the cutting front and kerf resulting from different processing conditions was observed by means of online high-speed X-ray diagnostics. The geometry of the interaction zone was recorded with a framerate of 1000 Hz during fusion cutting of 10-mm-thick samples of stainless steel. Comparing the results obtained with different shapes of the laser beam, it was found that the absorptivity is increased when the beam's longitudinal cross-section (parallel to the feed) is enlarged. Reducing the width of the beam in the transversal direction normal to the feed reduces the cross-sectional area of the cutting kerf. The findings show a good agreement with the geometric model which enabled the prediction of the absorptivity and the cross-sectional area of the cutting kerf and hence allows to reliably estimate the maximum cutting speed for different shapes of the laser beam, laser power, and sheet thicknesses. [ABSTRACT FROM AUTHOR]

Varnish removal from easel paintings is a restoration procedure that is regularly undertaken by cultural heritage conservators. In very few cases, traditional methods (chemical and mechanical) do not allow them to reach the goal of a perfectly controlled and selective cleaning. UV laser ablation has been considered since the 1990s to overcome these limitations, but its application to real cases is far from common practice. This study proposes a calibrated procedure based on ablation by an ns UV Nd:YAG laser at 266 nm combined with optical coherence tomography for micrometric laser varnish removal from inhomogeneous and highly photosensitive pictorial layers. The use of this wavelength for varnish removal, not adapted according to the literature, is discussed again after the beam shaping leading to a homogeneous and controlled intensity distribution. The innocuity is controlled by laser-induced luminescence, and some solutions for the transparency loss of the residual varnish following ablation are proposed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Precise knowledge about light propagation in biological tissues is necessary for accurate diagnostics and effective therapies utilizing optical technologies. In the current paper, the Monte Carlo simulation is applied to study light dispersion in normal and cancerous breast after irradiating to different laser beam shapes. Two distinct laser wavelengths (800–1100 nm) with planar and Gaussian shapes were employed. The spatially resolved steady-state diffuse reflectance of normal tissue and tumor was investigated using Monte Carlo simulation method via MCML and MCXLAB computations. The diffusion equation was solved to simulate the fluence rate at the tissue surface based on the optical parameter values (i.e., scattering and absorption coefficients). The results confirm differences in diffuse reflectance and optical fluence distribution between the normal and tumor tissues at each wavelength. Tissue optical parameters and the utilized laser beam shape control the distribution of the fluence rate within tissues. Therefore, offering visual representations of these distributions can provide a secure visual route for biological diagnostics. [ABSTRACT FROM AUTHOR]