Laser Beam Shaping Research Articles

High-power laser beam shaping using a metasurface for shock excitation and focusing at the microscale.

Achieving high repeatability and efficiency in laser-induced strong shock wave excitation remains a significant technical challenge, as evidenced by the extensive efforts undertaken at large-scale national laboratories to optimize the compression of light element pellets. In this study, we propose and model a novel optical design for generating strong shocks at a tabletop scale. Our approach leverages the spatial and temporal shaping of multiple laser pulses to form concentric laser rings on condensed matter samples. Each laser ring initiates a two-dimensional focusing shock wave that overlaps and converges with preceding shock waves at a central point within the ring. We present preliminary experimental results for a single ring configuration. To enable high-power laser focusing at the micron scale, we demonstrate experimentally the feasibility of employing dielectric metasurfaces with exceptional damage threshold, experimentally determined to be 1.1 J/cm2, as replacements for conventional optics. These metasurfaces enable the creation of pristine, high-fluence laser rings essential for launching stable shock waves in materials. Herein, we showcase results obtained using a water sample, achieving shock pressures in the gigapascal (GPa) range. Our findings provide a promising pathway towards the application of laser-induced strong shock compression in condensed matter at the microscale.

Design of a double lens freeform miniaturized antenna

The elliptical laser beam produced by a laser diode (LD) has asymmetrical divergence angle distribution and limits its application in long-distance space optical communication. In this paper, a double lens freeform miniaturized antenna design method is proposed to collimate, shape, and transmit elliptical beams from a LD. Based on the law of conservation of energy, refraction vector theory, equal optical path principle, and the three-dimensional point-by-point construction iterative method, two freeform surfaces on both lenses are constructed simultaneously. According to the simulation results, the maximum divergence angle of the output light is compressed to 4.92 µrad. The volume of the antenna is 1244.61cm3, which realizes the miniaturization of the antenna. In addition, the performance of the system is evaluated under different wavelength shifts, astigmatism based on the proposed improved line light source model, the offset of the light source, and the offset of both lenses. This paper provides a practical method for designing a simplified antenna that can collimate and shape laser beams and improve transmission efficiency. Furthermore, the proposed improved optimization method can provide a reference for the study of the initial parameters of lens freeform antennas.

Application of ultrafast laser beam shaping in micro-optical elements

The manufacturing and application of micro-optical elements are constantly evolving toward miniaturization, integration, and intelligence and have important applications in holographic displays, optical imaging, laser processing, information processing, and other fields. Ultrafast lasers, with their ultrashort pulse width, extremely high peak power, high processing resolution, small thermal influence zone, and nondestructive material processing advantages, have become an important processing method for preparing micro-optical elements. However, the laser output from the laser usually has a Gaussian distribution, with limitations in spatial and temporal energy and shape distribution, making it difficult to meet the requirements of processing efficiency and quality, which poses new challenges to ultrafast laser manufacturing technology. Therefore, by shaping the ultrafast laser beam and regulating nonlinear optical effects, the optimization and adjustment of the beam shape can be achieved, thus improving the quality and efficiency of micro-optical element processing. Ultrafast laser beam shaping technology provides a new method for the manufacture of micro-optical elements. This article first introduces the commonly used manufacturing methods for micro-optical elements. Second, from the perspective of the temporal domain, spatial domain, and spatiotemporal domain, the basic principles, methods, and existing problems of ultrafast laser beam shaping are summarized. Then, the application of these shaping technologies in the preparation of micro-optical elements is elaborated. Finally, the challenges and future development prospects of ultrafast laser beam shaping technology are discussed.

Laser beam shaping in an apodizer with a rectangular serrated aperture

Profile transformation of a uniform monochromatic beam with a flat wavefront after the propagation through an apodizer comprising a square serrated aperture and a spatial filter is theoretically considered at the apodizer exit and behind it. Main differences from the case of the circular apodizer geometry are shown. Roles of the square serrated aperture angles, the phase in Fresnel diffraction, the shape of the aperture serrations and serration height-to-period ratio are analyzed.

Laser beam shape optimization in powder bed fusion of metals

Laser beam shape optimization in powder bed fusion of metals

Broadband structured light using digital micro-mirror devices (DMDs): a tutorial

Laser beam shaping is a venerable topic that enjoyed an explosion in activity in the late 1990s with the advent of diffractive optics for arbitrary control of coherent fields. Today, the topic is experiencing a resurgence, fuelled in part by the emerging power of tailoring light in all its degrees of freedom, so-called structured light, and in part by the versatility of modern day implementation tools. One such example is that of digital micro-mirror devices (DMDs), for fast, cheap and dynamic laser beam shaping. In this tutorial we outline the basic theory related to shaping light with DMDs, give a practical guide on how to get started, and demonstrate the power of the approach with several case studies, from monochromatic to broadband light.

Partially coherent laser beam shaping in a zoom homogenizer.

This paper proposes a synthesis method including wave optics and geometric optics to design the zoom homogenizer for partially coherent laser beams and discusses the effects of the spatial coherence and system parameters on the beam performance. Based on the principles of pseudo-mode representation and matrix optics, a numerical model for fast simulation has been built and the parameter constraints for avoiding beamlet crosstalk have been presented. The relation of the size and the divergence angle of the highly uniform beams formed in the defocused plane with system parameters has been developed. The variations in the intensity profile and the uniformity of the variable-size beams during zooming have been explored.

Effects of Beam Shape on the Microstructures and Mechanical Properties during Thin-Foil Laser Welding

In this study, a fiber laser at a wavelength of 1070 nm with different beam shapes (spot, dough-nut, and spot-wobble) was used to weld thin 316 L stainless steel foils. The welding speed was varied from 400 to 1000 mm/s in the absence of shielding gas. The weld geometry, microstructure, lap shear strength, and crystallographic grain structure of the micro-joints were analyzed and correlated with the beam shape and welding speed. The results indicate that the laser beam shape significantly affected the weld width and penetration depth, and the best welding speed was 500 mm/s. This study proved for the first time that a spot-wobble laser beam could achieve better mechanical properties and microstructural characteristics than a doughnut beam during the high-power laser welding of thin-foil stainless steel plates.

The effect of incidence angle on the interaction of a pulse laser with ultra-high-performance concrete in the scabbling process

After prolonged service, concrete surfaces can develop a range of issues such as cracking, spalling, scaling, delamination, and contamination. Meanwhile, laser scabbling can be used as an advanced method for removing concrete surface defects. Besides, the downward direction is still mainly used in the scabbling process and variation in inclination angles of the laser beam has not been investigated in the laser scabbling process. In this study, nanosecond laser scabbling on Ultra-High Performance Concrete (UHPC) with different angles of the sample was carried out. The change in sample angle leads to changes in laser beam shape and the laser intensity distribution in the processing zone. The surface morphology and depth of the glassy layer were revealed by using a 3D Confocal Microscope corresponding to different incident angles of the laser beam. Moreover, a Scanning Electron Microscope (SEM) was also used to examine the pore size distribution in the glassy layer and heat-affected zone as compared to the non-processed zone. The molten material moved easily during the laser scabbling process as the inclination of the sample increased, causing the pores in the molten zone to collide and form a larger size.

A 3D Multiscale Model for Prediction of the Microstructure Evolution in Ti6Al4V Components Produced by Laser Powder Bed Fusion

A transient 3D multiscale model has been created to simulate the evolution of solidification microstructures rapidly and effectively in Ti6Al4V parts produced through Laser Powder Bed Fusion (LPBF). The microstructure simulation tool has been enhanced to account for rapid solidification conditions in Ti6Al4V alloys during processing of multi-layer multi-track LPBF parts. The simulation tool can evaluate the impact of part geometry, lase power input, laser speed, and laser beam shape on the formation of the microstructure in LPBF-processed Ti6Al4V alloy. The multiscale model considers several factors, including preferential crystallographic growth direction, isomorphism, epitaxy, melt pool motion, and temperature gradients to generate the observed texture and morphology of the microstructure in Ti6Al4V components. The model can evaluate various microstructure characteristics, such as grain size and texture. Consequently, it could aid in controlling the formation of solidification microstructures in Additive Manufacturing (AM) processed parts. The simulation tool has been previously validated by using IN625 laser remelting experiments made by National Institute of Standards and Technology. The 3D simulation tool can also be utilized to predict the microstructure formation in Ti6Al4V components produced by the Electron Beam AM processes.

Modeling optical fluence and diffuse reflectance distribution in normal and cancerous breast tissues exposed to planar and Gaussian NIR beam shapes using Monte Carlo simulation

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 (800-1100nm) 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.

Wide-spectrum laser beam shaping for full-color volume holographic optical element recording.

For homogeneous diffraction efficiency of the recorded volume holographic optical element (vHOE), a recording beam of uniform intensity is required. A multicolor vHOE is recorded by an RGB laser source with Gaussian intensity distribution; during equal exposure time, recording beams of different intensities would result in different diffraction efficiencies in different recording areas. In this paper, we present a wide-spectrum laser beam shaping system design method, by which the incident RGB laser beam can be controlled into uniform intensity distribution with a spherical wavefront. This beam shaping system can be added to any recording system to obtain uniform intensity distribution without altering the beam shaping effect of the original recording system. The proposed beam shaping system is composed of two aspherical lens groups, and the design method with an initial point design and optimization design method is given. An example is built to demonstrate the feasibility of the proposed beam shaping system.

Integration of Bragg gratings in aerosol-jetted polymer optical waveguides for strain monitoring capabilities.

We demonstrate and discuss the integration of Bragg gratings in aerosol-jetted polymer optical waveguides, produced in the optical assembly and connection technology for component-integrated bus systems (OPTAVER) process. By using a femtosecond laser and adaptive beam shaping, an elliptical focal voxel generates different types of single pulse modification by nonlinear absorption in the waveguide material, which are arranged periodically to form Bragg gratings. Integration of a single grating structure or, alternatively, an array of Bragg grating structures in the multimode waveguide yields a pronounced reflection signal with typical multimodal properties, i.e., a number of reflection peaks with non-Gaussian shapes. However, the main wavelength of reflection, located around 1555 nm, is evaluable by means of an appropriate smoothing algorithm. When loaded by mechanical bending, a pronounced Bragg wavelength shift of this reflected peak up to 160 pm is detected. This demonstrates that the additively manufactured waveguides can be used not only for signal transmission but also as a sensor.

Study of spatter net forming mechanism and penetration mode under flexible ring mode laser welding

Flexible ring mode (FRM) laser technology can generate different powers by adjusting the power ratio of the inner and outer rings, and has great potential for welding copper and its alloys with high reflectivity. This paper used a high-speed photographic camera to monitor the behavior and spatter-forming process of molten pool on the front of red copper plate. The spattering behavior in different penetration modes and net forming mechanisms under FRM are revealed. The results show that full penetration causes the high-temperature vapor to escape from the upper and lower openings. More energy is absorbed by the molten pool and keyhole in the semi-penetration mode, forming an expansion zone and increasing the pool's instability. The outer ring laser of FRM reduces the temperature gradient, which can lower the surface tension gradient, making the flow of the molten pool smoother and the height and formation times of the liquid column lower and less, thereby reducing the spatter. Moreover, FRM laser produces a larger and more stable keyhole, making the escape of metal vapor easier and minimizing the kinetic energy. The reasons above bring the sound result of high yield rate, improved by 75%, comparing with pure Gaussian laser. This paper provides theoretical guidance for engineering researchers to understand the role of shaping laser beams in the welding of highly reflective materials.

Effects of the adjustable ring-mode laser on intermetallic formation and mechanical properties of steel to aluminium laser welded lap joints

Research has confirmed a positive effect of laser beam shaping on controlling weld profiles and keyhole stabilisation, with significant reductions of porosity in weldments. However, few attempts with scattered results have studied the impact of laser beam shaping on intermetallicphase formation. This paper implements the adjustable-ring mode (ARM) laser and studies the impact of the core/ring power ratio to explore the impact on intermetallic phase formation and mechanical properties during remote laser welding of IF steel to 1050 aluminium. It was found that in conduction mode, the core/ring power ratio of 0.2 provided a larger surface area for bonding at the weld interface, and this was translated through the maximum lap-shear strength of 97.6 N/mm2 (joint efficiency 71%). Furthermore, this significantly reduced the Fe2Al5 intermetallic compound (IMC) thickness by 62% and total IMC thickness by 40% in contrast to a core-dominant beam (power ratio greater than one). In keyhole mode, cracking and lower lap-shear strengths were observed compared to the conduction mode. Notably, with a core/ring power ratio of 0.5 a significant grain refinement in the steel side of the weld was observed.

Toward Arbitrary Spin‐Orbit Flat Optics Via Structured Geometric Phase Gratings

AbstractReciprocal spin‐orbit coupling (SOC) via geometric phase with flat optics provides a promising platform for shaping and controlling paraxial structured light. Current devices, from the pioneering q‐plates to the recent J‐plates, provide only spin‐dependent wavefront modulation without amplitude control. However, achieving control over all the spatial dimensions of paraxial SOC states requires spin‐dependent control of corresponding complex amplitude, which remains challenging for flat optics. Here, to address this issue, a new type of flat‐optics elements termed structured geometric phase gratings is presented, that is capable of conjugated complex‐amplitude control for orthogonal input circular polarizations. By using a microstructured liquid crystal photoalignment technique, a series of flat‐optics elements is engineered and their excellent precision in arbitrary SOC control is shown. This principle unlocks the full‐field control of paraxial structured light via flat optics, providing a promising way to develop an information exchange and processing units for general photonic SOC states, as well as extra‐/intracavity mode convertors for high‐precision laser beam shaping.

RETRACTED: Effect of a variable laser beam profile system on productivity and surface quality of 316L stainless steel parts produced by Laser Powder Bed Fusion

Laser beam shaping promises to increase the productivity of layer-based Laser Powder Bed Fusion additive manufacturing. However, most non-Gaussian intensity profiles entail larger laser spots, reducing the resolution. This paper reports the development of a system incorporating a multi-core fiber laser capable of switching between small single mode beams and larger ring shapes within a layer. The intensity profiles were measured, and a model informed initial optimization showed at minimum 73% productivity increase by combining small single mode beam contour scans with wider ring-shaped fill scans while maintaining the high accuracy associated with using a small Gaussian beam.

Freeform surface design of laser beam shaping by iteration in two orthogonal directions (invited)

Freeform surface design of laser beam shaping by iteration in two orthogonal directions (invited)

Design of High-Smoothness Freeform Lens for Laser Beam Shaping

Design of High-Smoothness Freeform Lens for Laser Beam Shaping

Fabrication of large-scale scaffolds with microscale features using light sheet stereolithography.

The common characteristics that make scaffolds suitable for human tissue substitutes include high porosity, microscale features, and pores interconnectivity. Too often, however, these characteristics are limiting factors for the scalability of different fabrication approaches, particularly in bioprinting techniques, in which either poor resolution, small areas, or slow processes hinder practical use in certain applications. An excellent example is bioengineered scaffolds for wound dressings, in which microscale pores in large surface-to-volume ratio scaffolds must be manufactured - ideally fast, precise, and cheap, and where conventional printing methods do not readily meet both ends. In this work, we propose an alternative vat photopolymerization technique to fabricate centimeter-scale scaffolds without losing resolution. We used laser beam shaping to first modify the profile of the voxels in 3D printing, resulting in a technology we refer to as light sheet stereolithography (LS-SLA). For proof of concept, we developed a system from commercially available off-the-shelf components to demonstrate strut thicknesses up to 12.8 ± 1.8 μm, tunable pore sizes ranging from 36 μm to 150 μm, and scaffold areas up to 21.4 mm × 20.6 mm printed in a short time. Furthermore, the potential to fabricate more complex and three-dimensional scaffolds was demonstrated with a structure composed of six layers, each rotated by 45° with respect to the previous. Besides the demonstrated high resolution and achievable large scaffold sizes, we found that LS-SLA has great potential for scaling-up of applied oriented technology for tissue engineering applications.