Flat-top Beam Research Articles

Generation of the flat-top beam using convolutional neural networks and Gerchberg-Saxton algorithm

Abstract Laser technology has made rapid progress in recent years and has been widely used in various fields such as medicine, biology, military, and materials science. However, the limitations of traditional Gaussian intensity distribution of the laser beams in applications have prompted the emergence and development of flat-top beam shaping technology, which has received widespread attention. Here, we introduce a new method for generating flat-top beams that combines the traditional Gerchberg-Saxton algorithm with convolutional neural networks, using spatial light modulators to achieve flat-top beam shaping. A comparative analysis was conducted by comparing the root mean square error and diffraction efficiency of the generated flat-top beam with the results obtained using only the traditional Gerchberg-Saxton algorithm. Compared with the traditional Gerchberg-Saxton algorithm, the method proposed in this paper can generate a flat-top beam with smaller differences from the target light intensity and higher energy utilization, providing new possibilities for the application of laser technology.

Near-infrared double-layer cascaded metasurface for beam shaping

The vast applicability of collimated flat-topped beam shapers, predominantly constructed from traditional lens elements, is met with challenges when the scale is less than wavelength. Metasurfaces have an excellent ability for optical manipulation, which can provide a promising approach to flat optics. Here, a metasurface-based Gaussian beam shaper is designed to combine the transmission phase principle with geometric transformation methods, which can reshape a 1550 nm Gaussian beam into a flat-topped beam with a uniformity of 84.39%. Furthermore, a cascaded metasurface beam shaper design is proposed to address the significant divergence in the flat-topped beam obtained from the single-layer metasurface. Simulation results indicate the output beam exhibits both uniform intensity and phase distributions over a considerable transmission distance, effectively minimizing the divergence of the output beam. This research has potential applications in various fields, such as optical antennas, fiber optics, and other optical systems.

Picosecond pulsed flat-top beam in a mode-locking all-fiber laser

Picosecond pulsed flat-top beam in a mode-locking all-fiber laser

Optimization Algorithm for Flattop Beam Shaping Using Analytically Initial Phase

Optimization Algorithm for Flattop Beam Shaping Using Analytically Initial Phase

Elimination of chromatic aberration in high-order harmonic generation using a plasma-induced flat-top beam in a gas medium

Elimination of chromatic aberration in high-order harmonic generation using a plasma-induced flat-top beam in a gas medium

Characterizing the shaping, transmission, and amplification of near flat-top Gaussian beams through soft-edged apertures

The near flat-top Gaussian beam, which finds significant applications in energy amplification, laser processing, nonlinear frequency transformation, and atmospheric turbulence studies, has received limited attention regarding its transverse mode field distribution characteristics during spatial transmission and amplification. In this study, we simulated the spatial transmission and amplification processes of the near flat-top Gaussian beam using the Collins diffraction equation and a traditional side-pumping gain model. To validate our simulations, we conducted experiments employing a gradual soft-edged aperture to produce a near flat-top Gaussian beam. Our findings revealed that during free transmission, the near flat-top Gaussian beam evolved into a Gaussian-like beam, and a secondary peak emerged when amplified by a conventional laser diode side-pumping amplifier. These results underscored the necessity of using an image transfer system to maintain the energy uniformity of the near flat-top Gaussian beam during amplification. Furthermore, we identified the optimal shaping parameter of the Gaussian beam with a soft-edged aperture to be approximately 2.3. By utilizing an image transfer system and a two-stage amplifier, we successfully amplified the beam energy post-shaping. Ultimately, we achieved a near flat-top Gaussian beam with an energy of 219.5 mJ and an energy root-mean-square (RMS) normalized deviation of 0.144, compared to the initial Gaussian beam, which had an energy of 52.3 mJ and an energy RMS normalized deviation of 1.434.

High-fidelity metasurface holography illuminated by ultra-uniform flat-top beam generated through active wavefront shaping

High-fidelity metasurface holography illuminated by ultra-uniform flat-top beam generated through active wavefront shaping

Efficient Beam Manipulation With Phase Symmetry Operations on Transmitarrays for Flat-Top Beams

Efficient Beam Manipulation With Phase Symmetry Operations on Transmitarrays for Flat-Top Beams

Near-field propagation of a flat-topped gaussian beam: analysis in weakly ‎turbulent atmospheres

We investigate the analysis of optical communication employing the shape beams, definitely concentrating on the effect of factors on the physical characteristics of a Flat Top Gaussian (FTG) beam. The propagation of a beam of laser light in the atmosphere layer is disposed to being affected by many optical phenomena such as scattering, absorption, and turbulence. These phenomena arise from differences in the scintillation index and the intensity modes realized in the source and receiver planes. This work is a numerical investigation of the FTG laser beam as it beams trekking through a zone of low turbulence using open-source software. This simulation will be conducted using a mathematical model derived from the split-step beam propagation technique. The intensity distributions of the source plane and the average intensity is received in air turbulence are computed, with an extra contour at the transducer plane. The Rytov approach to develops the scintillation index, structural constant, source size, and supplementary parameters to measure the weak turbulent model. Furthermore, these factors are studied in the context of near-field propagation. Also, the impression of the scintillation and wander of the beam is assessed. All simulated results are analyses and contrasted with the TEM00 Gaussian beam. At last, these discoveries are compared with the data obtained in the experimental piece of the study, additionally by applied in laser applications.

Design of a long depth of focus Gaussian beam shaping system via aspheric lenses

This paper presents a beam shaping system that uses a Galilean beam shaper. The light mapping function and the aspherical coefficient, which determines the characteristics of the aspheric lens, are derived based on the law of conservation of energy. Furthermore, optical software (i.e., ZEMAX) was utilized to simulate the design of the shaping system. In addition, a spherical collimation system is introduced to achieve the shaping system with long depth of focus. The results show that the output flat-top beam has the uniformity over 90% within the 300mm depth of focus range and the divergence angle no more than 0.6°, which is in line with the theoretical expectation. Compared to the previous works, our beam shaping system is characterized by long depth of focus, simple structure and good beam shaping effect, which makes the present shaping beam more flexible for the application in the field of laser processing.

Hot Crack Formation Mechanism and Inhibition of a Novel Cobalt-Based Alloy Coating during Laser Cladding.

Laser cladding provides advanced surface treatment capabilities for enhancing the properties of components. However, its effectiveness is often challenged by the formation of hot cracks during the cladding process. This study focuses on the formation mechanism and inhibition of hot cracks in a novel cobalt-based alloy (K688) coating applied to 304LN stainless steel via laser cladding. The results indicate that hot crack formation is influenced by liquid film stability, the stress concentration, and precipitation phases. Most hot cracks were found at 25°-45° high-angle grain boundaries (HAGBs) due to the high energy of these grain boundaries, which stabilize the liquid film. A flat-top beam, compared to a Gaussian beam, creates a melt pool with a lower temperature gradient and more mitigatory fluid flow, reducing thermal stresses within the coating and the fraction of crack-sensitive, high-angle grain boundaries (S-HAGBs). Finally, crack formation was significantly inhibited by utilizing a flat-top laser beam to optimize the process parameters. These findings provide a technical foundation for achieving high-quality laser cladding of dissimilar materials, offering insights into optimizing process parameters to prevent hot crack formation.

Experimental system and method of aerobic thermal environment simulation based on laser heating

Considering the superior luminous intensity characteristics of lasers, a thermal simulation platform employing laser-induced heating in an aerobic environment was developed. Achieving a uniformly distributed flat-topped square laser beam output was facilitated through optical fibre bundling techniques, while precise control over laser power output was attained through current modulation. Utilising the aforementioned system, thermal shock simulation experiments were conducted in an aerobic environment, subjecting two types of high-temperature-resistant composites, namely C/C and C/SiC, to temperatures up to 1800 °C. These composites were lightweight, heat-resistant materials designed for hypersonic vehicle applications. The results show that the system and method can be used to simulate high temperatures, rapid temperature increases, and thermal shocks on C/C composite materials, with minimal variation in the coupling coefficient under aerobic conditions. The system and method can also provide key technology support for thermal-force-oxygen coupling testing of high temperature resistant materials.

Effect of 980 nm Laser Photobiomodulation Using Flat-Top Beam Profile Modifier in Acceleration of Canine Retraction: A Randomized Clinical Trial

Effect of 980 nm Laser Photobiomodulation Using Flat-Top Beam Profile Modifier in Acceleration of Canine Retraction: A Randomized Clinical Trial

Dynamical characteristics of tightly focused flat-topped double vortex beam for enhanced optical manipulation

The Flat-topped Vortex (FTV) beam has shown remarkable utility in a diverse range of industrial procedures, primarily attributed to its central intensity plateau. Nevertheless, the substantial potential of the FTV beam in particle trapping and manipulation has been largely underappreciated. In this work, we conducted the first study on the focusing properties and dynamic characteristics of the Flat-topped double vortex (FTDV) beam under different polarization for the absorption of Rayleigh particles. Through superimposing linearly two FTV beams with equal but opposite topological charges, the FTDV beam emerged naturally. Moreover, a comprehensive numerical analysis was subsequently performed to decode the interactions between the focusing field of the FTDV beam and Rayleigh particles. The analysis demonstrated that the focusing field of FTDV beam can perform multi-particle capture and effectively manipulate particles by modulating the topological charge |m|, the flatness order n, and the polarization state of the FTDV. Furthermore, a comparison between the focusing field of FTDV beam with that of vector vortex (VV) beam revealed that the FTDV beam was capable to generate spin angular momentum (SAM) density and spin torque at least an order of magnitude higher. These findings highlight the superior capabilities of FTDV beam in optical manipulation, and provide essential theoretical support for its utilization in particle capture and management.

Simulation of melt kinetics of in-situ molding of thermoplastic CF/PEEK composites

To reveal the interaction mechanism between the composites and the laser during the laser in-situ forming process of carbon fiber composites, the temperature change history and phase transition process on the surface of CF/PEEK composites under the action of flat-top beams with different moving directions were simulated by using COMSOL Multiphysics finite element simulation software. The results show that, due to the anisotropy of CF/PEEK composites, the transverse spread of the temperature field is always larger than the longitudinal spread, and when the moving angle is less than 45°, the surface temperature and the surface heat-affected zone of CF/PEEK composites increase with the increasing of the moving angle. The surface temperature and the area of heat affected zone are maximum when the angle of movement is 45°. As the angle of movement increases from 45° to 90°, the area and temperature of the heat-affected zone on the surface of the composite decreases with the increase in the angle of movement. The area of the melting zone is consistent with the distribution of the temperature field on the composite surface. The transverse broadening of the melting zone is always larger than the longitudinal broadening. The area of the melting zone is largest when the laser spot moves at an angle of 45°, and the area of the melting zone is smallest when the spot moves at an angle of 90°.

Design of a Compact Log Periodic Dipole Array Antenna for Broadband and High-Power Beam Synthesis Using Superposition

This paper investigates various array beam shapes for high-power electronic warfare applications using an actual broadband array antenna. For use in a limited mounting space, a compact printed log periodic dipole array (LPDA) operating over a wide bandwidth is designed. The LPDA is then extended to an 8 × 1 array, with active element patterns (AEPs) obtained through simulation and measurement. Beam synthesis is performed by the superposition of several array patterns, which involves adjusting the weight of each AEP. To derive a synthesized array beam shape that is similar to the guided mask, the Taylor window weighting method is applied to each array pattern. Finally, beam synthesis for the flat-top beam, cosecant-squared beam, and iso-flux beam is performed using Taylor window-weighted AEPs, and the results are compared with those of beam shapes using ideal isotropic patterns. The results demonstrate that various beam shapes can be achieved for high-power electronic warfare applications using the AEPs of an actual array antenna.

Evaluating the effectiveness of two wavelengths of 810 and 980 nm Diode laser with two different beam profiles on tooth discoloration in bleaching: an experimental study

Teeth color has a significant impact on facial aesthetics. Tooth bleaching is the safest way to lighten the color of your teeth. Today, hydrogen peroxide is the most commonly used bleaching agent. The diode laser is one of the light sources that speeds up the bleaching process. One of the laser beam features is the laser beam profile, which depicts the distribution of laser intensity across the beam section. The goal of this study is to look into the effectiveness of Gaussian and Flat top beam profiles on tooth shade using two diode laser wavelengths of 810 and 980 nm in the tooth bleaching process. Fifty human anterior and premolar teeth were extracted and placed in a tea and coffee solution for three weeks before being divided into five groups. The first group did not receive laser radiation because 40% hydrogen peroxide was used; in the second and third groups, the profile of the flat top beam and the wavelength were 810 and 980 nm, respectively; and in the fourth and fifth groups, the wavelength of the Gaussian beam profile was 810 and 980 nm. The shade of the samples before and after bleaching was measured with a CIELab-based spectrophotometer, and the results were analyzed using one-way ANOVA and Tukey’s multiple comparison test. All bleaching methods resulted in a significant change in tooth color (ΔE>3.3). There was a significant difference in average shade changes across groups (P<0.001). The highest degree of shade change was observed in two groups of lasers with a wavelength of 980 nm and profiles of Flat top beam (ΔE=5.35) and Gaussian (ΔE=5.02). There were no differences between the remaining groups. We conclude that the 980 nm wavelength produces a greater shade change than the 810 nm wavelength and chemical method. The diode laser’s 810 nm wavelength has no effect on the shade of teeth.

Polarization singularities for shaping of vector flat-top beams in utilization for high-power laser micromachining of various materials

Structured light is desired in the micromachining of various materials. As the latest ultrashort laser sources increase the average power by increasing the repetition rate, the efficiency of the process becomes crucial in laser micromachining. The standard Gaussian beam shape, because of its slow ascending/descending slope, is not the most efficient beam, neither in precise energy deposition nor in heat management. Flat-top beams are required for precise and even energy distribution and are used in laser ablation or thin-film removal. We look at a rather abstract concept of polarization singularities and investigate them to create a vector flat-top beam. For this purpose, we devise a beam-shaping method based on the volumetric birefringent nano gratings which allow the generation of high-energy polarization singularities. By tuning the input beam waist, we have generated three most common laser micromachining beam profiles (Gaussian, Flat-top, and ring- or doughnut-shaped). The resulting high-quality and high-energy polarization singularities allow us to systematically demonstrate their use in transparent and opaque material micromachining, as well as the usual application for flat-top beams of thin-film removal.

On the role of flat-top beam in pore elimination and fatigue performance of Ti-6Al-4V fabricated by laser powder bed fusion

It's unavoidable to produce defects in the repeated layer-by-layer manufacturing process of laser powder bed fusion (LPBF). This limits the application of LPBF for safety–critical parts. The formation of defects is closely related to the interaction between the laser beam and material in the molten pool. In this paper, beam shaping was used to improve the building quality of LPBF. Process parameter optimization was performed to obtain samples with the fewest defects. Heat treatment was also employed to further improve the mechanical properties. The results showed that the obtained flat-top beam significantly reduced the propensity for keyhole pore formation and enlarged the process windows. In-situ heat treatment induced by high heat input led to the decomposition of martensite and improved the fatigue crack growth (FCG) threshold (∼3.7 MPa m0.5) of the as-built samples. After heat treatment (annealed and solution/aged), the FCG threshold further increased to 5.5/6.3 MPa m0.5, respectively. Reduced defects and high FCG resistance resulted in a fatigue limit above 600 MPa (N = 1e7, R = 0.1), which is comparable to wrought and aged Ti-6Al-4V parts. This study demonstrates the feasibility of improving molten pool stability and reducing defects through beam shaping, providing a new approach to manufacturing high-quality LPBF parts.

Performance optimization of a SERF atomic magnetometer based on flat-top light beam

We explore the impact of pumping beams with different transverse intensity profiles on the performance of the spin-exchange relaxation-free (SERF) atomic magnetometers (AMs). We conduct experiments comparing the traditional Gaussian optically-pumped AM with that utilizing the flat-top optically-pumped (FTOP) method. Our findings reveal that the FTOP-based approach outperforms the conventional method, exhibiting a larger response, a narrower magnetic resonance linewidth, and a superior low-frequency noise performance. Specifically, the use of FTOP method leads to a 16% enhancement in average sensitivity within 1 Hz–30 Hz frequency range. Our research emphasizes the significance of achieving transverse polarization uniformity in AMs, providing insights for future optimization efforts and sensitivity improvements in miniaturized magnetometers.