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Bayesian Optimization of a Free-Electron Laser
摘要： The Linac coherent light source x-ray free-electron laser is a complex scientific apparatus which changes configurations multiple times per day, necessitating fast tuning strategies to reduce setup time for successive experiments. To this end, we employ a Bayesian approach to maximizing x-ray laser pulse energy by controlling groups of quadrupole magnets. A Gaussian process model provides probabilistic predictions for the machine response with respect to control parameters, enabling a balance of exploration and exploitation in the search for the global optimum. We show that the model parameters can be learned from archived scans, and correlations between devices can be extracted from the beam transport. The result is a sample-efficient optimization routine, combining both historical data and knowledge of accelerator physics to significantly outperform existing optimizers.
关键词： Bayesian optimization,accelerator physics,free-electron laser,Gaussian process
更新于2025-09-23 15:19:57
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Top-hat and Gaussian laser beam smoothing of ground fused silica surface
摘要： Laser smoothing is a promising technique for processing optical glass due non-contact characteristics and easy-adaptability to non-spherical surfaces. The smoothing effects of CO2 laser of top-hat and Gaussian intensity on ground fused silica surfaces were examined in the work. The results show that ground surface with surface micro-roughness of 500 nm (RMS) can be smoothed to < 0.5 nm (RMS) with both intensity profiles. Best surface roughness rises with increasing power density of laser and therefore lower power density combined with slow scanning speed is favored to improve surface quality. Numerical model was established to investigate thermal and hydrodynamic transient process to elucidate the underlying mechanism. Simulations show that smoothing process takes place at the same time as the temperature rises due to ever-decreasing viscosity of fused silica. Beam shaping is able to reduce peak power density of high power processing laser and smoothing efficiency might be increased without the loss of the processed quality of glass.
关键词： Laser smoothing,Roughness,Top-hat beam,Gaussian beam,Fused silica,Laser polishing
更新于2025-09-23 15:19:57
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Transient optics of gold during laser irradiation: From first principles to experiment
摘要： Intense femtosecond laser pulses can induce dramatic changes on different properties of materials. Laser induced changes of the optical properties are particularly relevant, since they can lead to a modi?cation of the amount of energy that the material absorbs from the laser pulse. In noble metals, changes of re?ectivity upon femtosecond laser illumination are expected to be strong due to the excitation of d electrons. In this work we perform measurements of the re?ectivity of laser excited gold in the infrared and in the ultraviolet range, respectively. We ?nd a remarkable dependence of the re?ectivity on laser ?uence, which is in turn different in both ranges of photon energy. In order to understand the behavior of the re?ectivity in laser excited solids and to explain our measured re?ectivity curves we develop a theoretical scheme in the framework of the two-temperature model with the electronic temperature as the key parameter. Our approach is based on all-electron calculations of the interband contribution to the re?ectivity and a careful determination of the intraband, Drude-like terms and a realistic model for the space and time resolved energy transfer from a Gaussian laser pulse into the electronic system. We obtain very good agreement between experiment and theory and identify the main mechanisms for re?ectivity changes as a function of laser ?uence.
关键词： intraband,Drude-like terms,interband contribution,electronic temperature,Gaussian laser pulse,re?ectivity,two-temperature model,femtosecond laser pulses,optical properties,gold
更新于2025-09-23 15:19:57
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[IEEE 2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) - Singapore, Singapore (2018.4.22-2018.4.26)] 2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) - Optical Coupling of 3D Silicon Micromirrors
摘要： Free space optical coupling is considered the important feature which affects on the performance of the optical systems. Where coupling elements such as lenses and mirrors are aided in overcome the divergence of the Gaussian beams and to achieve phase matching. Here we concentrate on the studying of the free space coupling of 3D (spherical) mirror based on the propagation of a Gaussian beam. The design and fabrication of 3D mirror in the Optical microelectromechanical systems (MEMS) are studied. The coupling efficiency is a very important factor in the design of any MEMS circuit. High coupling efficiency is obtained by assembling optical parts which increase the integration effort. In this work, we report a high coupling efficiency, monolithically integrated 3D silicon micromirror that is capable of influencing on the Gaussian beams which propagate in the plane of the silicon substrate. A micromachining method is presented for fabricating the 3D micromirror.
关键词： micromachining,3D silicon micromirrors,optical coupling,MEMS,Gaussian beams
更新于2025-09-23 15:19:57
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Generation of pure Laguerre-Gaussian vector beams on the higher-order Poincaré sphere by hollow Gaussian beams through dielectric metasurfaces
摘要： It is a longstanding challenge for the extracavity generation of vector beams (VBs) to have pure Laguerre-Gaussian (LG) modes due to diffraction. Here we propose theoretically and realize experimentally the generation of pure LG VBs by using hollow Gaussian beams (HGBs) through q-plates. A general expression for the VB generated by the HGB with arbitrary polarization is derived. It is found that when the order of the HGB is two times the topological charge of the q-plate, the VB possesses a pure LG mode and that any desired polarization distribution on the higher-order Poincaré sphere can be realized by tuning the incident polarization. Further we implement the q-plates with dielectric metasurfaces and experimentally verify the theoretical results. The generated pure LG VB may find applications in the situations where high mode purity is required.
关键词： Vector beam,Laguerre-Gaussian mode,Diffraction,Metasurfaces,Pancharatnam-Berry phase,Hollow Gaussian beam
更新于2025-09-19 17:15:36
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Vortex solitons in Bose–Einstein condensates with spin–orbit coupling and Gaussian optical lattices
摘要： We investigate the generation and stability of three-dimensional (3D) solitons in binary atomic Bose–Einstein condensates with spin–orbit coupling (SOC) and Super-Gaussian optical lattices. We examine the stability of 3D solitons using their norm and energy. The evolution of solitons is made more stable and their resistance to collapse more robust by the introduction of Gaussian lattices. Depending on the relative strength of SOC, the nonlinearity modulation parameter, and the lattice parameters, we observe stable solitons of the semi-vortex and mixed-mode type. In addition, we demonstrate the robustness of solitons in propagation and collisions.
关键词： Spin–orbit coupling,Gaussian lattices,Bose–Einstein condensates,Vortex solitons
更新于2025-09-19 17:15:36
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Optimal Gaussian measurements for phase estimation in single-mode Gaussian metrology
摘要： The central issue in quantum parameter estimation is to find out the optimal measurement setup that leads to the ultimate lower bound of an estimation error. We address here a question of whether a Gaussian measurement scheme can achieve the ultimate bound for phase estimation in single-mode Gaussian metrology that exploits single-mode Gaussian probe states in a Gaussian environment. We identify three types of optimal Gaussian measurement setups yielding the maximal Fisher information depending on displacement, squeezing, and thermalization of the probe state. We show that the homodyne measurement attains the ultimate bound for both displaced thermal probe states and squeezed vacuum probe states, whereas for the other single-mode Gaussian probe states, the optimized Gaussian measurement cannot be the optimal setup, although they are sometimes nearly optimal. We then demonstrate that the measurement on the basis of the product quadrature operators ^X^P + ^P^X, i.e., a non-Gaussian measurement, is required to be fully optimal.
关键词： Gaussian states,Fisher information,optimal measurements,quantum metrology,phase estimation
更新于2025-09-19 17:15:36
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Nonlinear Electrothermal Model for Investigating Transient Temperature Responses of a Through-Silicon Via Array Applied With Gaussian Pulses in 3-D IC
摘要： In this paper, a through-silicon via (TSV) array under Gaussian pulse is studied comprehensively with a rigorous consideration of its electrothermal characteristics. To enhance the computational efficiency and reduce the memory cost, we develop a unified radial point interpolation method (RPIM) to handle these TSV electrothermal coupling problems. The comparison between the results of the proposed formulas and fine-grid finite-element method (FEM) shows that the RPIM has a very high accuracy and reduces computational time by up to 88% in comparison with the fine-grid FEM. The transient temperature responses are studied in detail for three layouts of single-layered TSV arrays with different silicon dioxide layer thicknesses and areas enclosed by TSVs. Furthermore, the two-layered TSV array structure including microbumps and RDLs is simulated electrothermally to verify the scalability of this method. Our work demonstrated the capability of addressing a large number of TSV arrays and the proposed method enables faster and more accurate electrothermal design of TSV-based 3-D ICs.
关键词： transient temperature,Electrothermal,through silicon vias (TSV),radial point interpolation method (RPIM),TSV array,Gaussian pulse
更新于2025-09-19 17:15:36
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Sparse Representation for Color Image Super-Resolution with Image Quality Difference Evaluation
摘要： The sparse representation models have been widely applied in image super-resolution. The certain optimization problem is supposed and can be solved by the iterative shrinkage algorithm. During iteration, the update of dictionaries and similar patches is necessary to obtain prior knowledge to better solve such ill-conditioned problem as image super-resolution. However, both the processes of iteration and update often spend a lot of time, which will be a bottleneck in practice. To solve it, in this paper, we present the concept of image quality difference based on generalized Gaussian distribution feature which has the same trend with the variation of Peak Signal to Noise Ratio (PSNR), and we update dictionaries or similar patches from the termination strategy according to the adaptive threshold of the image quality difference. Based on this point, we present two sparse representation algorithms for image super-resolution, one achieves the further improvement in image quality and the other decreases running time on the basis of image quality assurance. Experimental results also show that our quantitative results on several test datasets are in line with exceptions.
关键词： generalized Gaussian distribution feature,image super-resolution,fast iterative shrinkage algorithm,sparse representation,image quality difference
更新于2025-09-19 17:15:36
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Propagation Property of an Astigmatic sin–Gaussian Beam in a Strongly Nonlocal Nonlinear Media
摘要： Based on the Snyder and Mitchell model, a closed-form propagation expression of astigmatic sin-Gaussian beams through strongly nonlocal nonlinear media (SNNM) is derived. The evolutions of the intensity distributions and the corresponding wave front dislocations are discussed analytically and numerically. It is generally proved that the light field distribution varies periodically with the propagation distance. Furthermore, it is demonstrated that the astigmatism and edge dislocation nested in the initial sin-Gaussian beams greatly influence the pattern configurations and phase singularities during propagation. In particular, it is found that, when the beam parameters are properly selected, a vortex beam with perfect doughnut-shaped profile can be obtained for astigmatic sin-Gaussian beams with two-lobe pattern propagating in SNNM.
关键词： nonlocal nonlinear medium,screw dislocation,vortex,astigmatic sin–Gaussian beam,edge dislocation
更新于2025-09-19 17:15:36