Neural networks have provided faster and more straightforward solutions for laser modulation. However, their effectiveness when facing diverse structured lights and various output resolutions remains vulnerable because of the specialized end-to-end training and static model. Here, we propose a redefinable neural network (RediNet), realizing customized modulation on diverse structured light arrays through a single general approach. The network input format features a redefinable dimension designation, which ensures RediNet wide applicability and removes the burden of processing pixel-wise light distributions. The prowess of originally generating arbitrary-resolution holograms with a fixed network is first demonstrated. The versatility is showcased in the generation of 2D/3D foci arrays, Bessel and Airy beam arrays, (perfect) vortex beam arrays, and even snowflake-intensity arrays with arbitrarily built phase functions. A standout application is producing multichannel compound vortex beams, where RediNet empowers a spatial light modulator (SLM) to offer comprehensive multiplexing functionalities for free-space optical communication. Moreover, RediNet has the hitherto highest efficiency, only consuming 12 ms (faster than the mainstream SLM framerate of 60 Hz) for a 10002-resolution holograph, which is critical in real-time required scenarios. Considering the fine resolution, high speed, and unprecedented universality, RediNet can serve extensive applications, such as next-generation optical communication, parallel laser direct writing, and optical traps.
Aiming at tightly focusing vector polarized partially coherent vortex laser beams, this paper introduced a new kind of vortex beams, named radially polarized multi-Gaussian Schell-model (MGSM) power-exponent-phase vortex beam (PEPVB). Based on the vectorial diffraction theory, this work theoretically and numerically investigated the tight focusing properties of radially polarized MGSMPEPVB passing through a high numerical aperture objective lens. Thus, we analyzed the impact of topological charge, power exponent, beam index and coherence length on the intensity of focal zone. We discovered that by increasing beam index, the intensity distribution of focal plane gradually changed from Gaussian to flat-top. Especially, when the power exponent was a non-negative fraction close to 1, regardless of whether the topological charge was an integer or not, the circular symmetry of the focused spot at focal plane would be destroyed, showing a non-uniform and asymmetric central dark core optical intensity distribution. Besides, the value of the fractional part of the topological charge would make the hollow structure of the central dark core fully open due to the introduction of power-exponent phase, which is an improvement over the tight focusing properties of radially polarized MGSM vortex beams. This work has clearly demonstrated that by changing the values of topological charge, power exponent, beam index and coherence length, the special focal spot structures with different intensity distributions including flat-top beam and irregular hollow beam can be obtained, which have many potential applications in laser machining and particle capturing such as manipulation of certain irregular microparticles.
By utilizing customized intra-cavity optical elements including graded-phase mirrors, variable reflectivity mirrors, aspherical mirrors, diffractive optical elements and spatial light modulators, the mode discrimination of the cavity is enhanced and a pre-determined transverse mode, usually flat-top beams such as super-Gaussian beams or flattened- Gaussian beams, can be generated in the cavity. The design of such laser cavities oscillating in a predetermined transverse mode is commonly based on the concept of phase conjugation, whereby the desired phase profile of optical element is obtained by reversely propagating the predetermined transverse mode and creating a conjugate field to propagate back. However, this procedure is only accurate under the assumption that the mirror size is infinite and the propagation process is in a lossless manner. Moreover, the parameters of the pre-determined mode, such as beam size and amplitude distribution, must be carefully chosen or else non-negligible errors would occur due to finite-size apertures and associated truncation. Here, we report on a simple and effective approach for intra-cavity mode control based on optimizing the single-mode power factor, which represents the total power extracted by a single mode from the active medium. By optimizing the single-mode power factor of the desired mode, the cavity can be designed to operate in mono-mode, increasing the mode purity significantly. Our method is verified on a digital laser with a spatial light modulator as the rear mirror and the loaded phase profile is acquired by a simulated annealing algorithm. As a result, when the single-mode power factor of TEM00 mode is optimized, the resonator operates in a single fundamental mode. When the single-mode power factor of the vortex mode with a topological charge of 1 is optimized, the output mode purity is close to 100%.
The Galvanized steel sheet is used as the automotive body material, and the evaporation of zinc into the weld seam will cause welding defects during the laser welding process. The multi-point laser beam has great development potential in automobile industry, because it can effectively reduce the integration of the galvanized layer into the weld seam during welding. In this paper, a panda-shaped three-point beam (panda beam) is proposed to replace the original single beam used in welding and three methods to realize the panda beam have been discussed. The beam splitting of the diffraction grating is performed, and the three, five and four beam-splitting ratio Daman gratings are obtained but with relatively high energy loss. Additionally, based on the theory of grating diffraction, a panda beam has been obtained by splitting the 4kW incident laser through the Bragg grating. The single front beam radius is 0.6mm with a power of 1.1261kW, and the distance between the two front beams is 3.8mm. The radius of the main beam is 1mm with a power of 1.7168kW, and the distance from the front beam to the main beam is 9.7mm. Lastly, based on the beam splitting theory of geometric optics, the multi-point beam and the panda beam are realized by the ridge reflector with an energy loss of 14.09%, which shows the great advantage of laser beam splitter compared with multi-light source structure in practical application. When welding with the panda beam, two functions of zinc coating and solder melting are carried out respectively, which can avoid zinc vapor entering the molten pool and improve the welding quality
As a mid-infrared laser with large magnification and high beam quality, carbon dioxide lasers are often used as intermediate amplifiers in picosecond terawatt laser systems. With the combination of gas discharge and optical pump, the gain spectrum in 10μm can be greatly improved. In this paper, a numerical model is set up to describe the laser amplification and kinetic processes, based on six-temperature level structure, in hybrid pump CO2 laser amplifier system. The influences of the pump power and its amplification results compared with conventional CO2 laser are simulated and discussed. Such a hybrid pump CO2 laser amplifier is very promising in improving output pulse quality by reducing the pulse split.
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