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Impact of Nonlinear Kerr Effect on the Focusing Performance of Optical Lens with High-Intensity Laser Incidence
摘要： The rapid development of high-energy and high-power laser technology provides an important experimental means for the research of extreme physical state in the laboratory and for the design of large laser facilities for realizing inertial con?nement fusion. However, when the incident laser ?eld is very strong, the Kerr e?ect of materials a?ects the nominal performance of optical elements. In this work, the impact of Kerr e?ect on the focusing performance of an optical lens is studied by calculating and comparing the ?led patterns of focal spots for three di?erent incident laser beams together with three di?erent levels of light intensities. The traditional transfer function of an optical lens is ?rstly modi?ed according to the theory of nonlinear Kerr e?ect. We use the two-dimensional fast Fourier transform algorithm and angular spectrum algorithm to numerically calculate the ?eld distributions of focal spots in the nominal focal plane of lens and its adjacent planes based on the Fresnel di?raction integral formula. The obtained results show that the Kerr e?ect a?ects the focusing characteristics of lens, especially for the incidence of high-order Gaussian beams, such as Hermite-Gaussian beams and Laguerre-Gaussian beams. At the same time, the focal length and refractive index of lens also change the ?eld patterns of focal spots. The presented methodology is of great value in engineering applications where the practical problem with beam size up to 100 mm can be calculated using a common laptop computer. The work provides an e?cient numerical technique for high-intensity incident laser beams focused by lens that takes Kerr e?ect into consideration, which has potential applications in high energy density physics and large laser facilities for inertial con?nement fusion.
关键词： Kerr effect,optical lens,numerical analysis,focal spot,high-intensity laser
更新于2025-09-23 15:21:01
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Detection of the focal spot motion relative to the collimator axis of a linear accelerator under gantry rotation
摘要： The potential for delivering high precision radiotherapy using linear accelerators (linacs) has been improved with the development of digital x-ray electronic portal imaging devices (EPID) for acquiring kilovoltage (kV) cone-beam CT and megavoltage (MV) images for patient positioning. EPIDs have also opened the possibilities of developing novel quality assurance and insight into radiotherapy equipment performance. The aim of this work was to measure the offset of the focal spot position (FSP) of a linac under gantry rotation relative to the collimator axis using an EPID. The focal spot was assumed to be a point source of MV x-ray generation. A special phantom was designed for attachment to the gantry head and supporting two tungsten-carbide ball-bearings at two different distances from the focal spot. The methodology was demonstrated on a series of images acquired of the phantom on three Elekta linacs in clinical use with 6 MV flattening-filter-free (FFF) beams. The gantry and collimator were rotated 360° in steps of 30°. For each position an image of the phantom was acquired using the EPID. Each series consisted of 169 EPID images. The images were analysed using in-house developed software. Analyses of the EPID images acquired with 6 MV FFF beams showed that the focal spot motion amplitudes relative to the collimator axis during gantry rotation in the longitudinal and lateral directions were less than 0.10 mm and 0.50 mm, respectively, for an optimized 6 MV FFF FSP calibrated linac.
关键词： MV radiation,focal spot,ball-bearing,EPID,collimator,linear accelerator
更新于2025-09-23 15:19:57
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Application of harmonics imaging to focal spot measurements of the “PETAL” laser
摘要： By using numerical simulations and experimental campaigns on a small-scale laser facility, the concept of the focal spot imaging on harmonics of laser frequency is developed and implemented on the Laser MegaJoule (LMJ)/PETawatt Aquitaine Laser (PETAL) facility. The Two/Three ω Imaging System was activated and validated during the first 2017–2019 interaction campaigns of PETAL on the LMJ. It provides major information on focal spot characteristics on a target. Such an approach could be easily applied to any high-intensity facility in the relativistic intensity regime (>1018 W cm?2).
关键词： PETAL laser,harmonics imaging,high-intensity laser-plasma interaction,focal spot measurements
更新于2025-09-16 10:30:52
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Effect of Small Focus on Electron Heating and Proton Acceleration in Ultrarelativistic Laser-Solid Interactions
摘要： Acceleration of particles from the interaction of ultraintense laser pulses up to 5 × 1021 W cm?2 with thin foils is investigated experimentally. The electron beam parameters varied with decreasing spot size, not just laser intensity, resulting in reduced temperatures and divergence. In particular, the temperature saturated due to insufficient acceleration length in the tightly focused spot. These dependencies affected the sheath-accelerated protons, which showed poorer spot-size scaling than widely used scaling laws. It is therefore shown that maximizing laser intensity by using very small foci has reducing returns for some applications.
关键词： proton acceleration,focal spot size,ultrarelativistic laser-solid interactions,electron heating,laser intensity
更新于2025-09-16 10:30:52
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Influence of focal spot diameter and beam oscillation on the process efficiency of laser beam welding utilizing a direct diode laser
摘要： Costs of power consumption, efficiency improvement and a green image are increasing issues for automotive manufacturers. One possibility to reduce energy consumption is to increase process efficiency of the established laser beam welding. For this reason this contribution examines whether the laser output power of a direct diode laser can be reduced whilst keeping weld seam volumes constant. This is realized by a reduced spot diameter from initial 664 μm to 368 μm in combination with beam oscillation in order to generate blind seams in 22MnB5 and DC01 steel. It is shown that energy consumption can be reduced significantly.
关键词： Energy efficiency,Oscillation,Focal spot diameter,Direct-diode laser,Automotive
更新于2025-09-12 10:27:22