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Non-paraxial theory of self-focusing/defocusing of Hermite cosh Gaussian laser beam in rippled density plasmas
摘要： Present research work focuses on study of self-focusing and self-trapping of Hermite cosh Gaussian (HchG) laser beams in rippled density plasma by considering relativistic non-linearity. The coupled non-linear differential equations for the beam width parameters (for modes m = 0, 1, and 2) were derived by employing higher-order correction in comparison to paraxial ray theory by expanding dielectric function and eikonal up to r4 terms. It is observed that the inclusion of higher-order terms significantly influence the off-axial properties for m ≥ 1 mode indices. Furthermore, the effect of parameters including beam intensity, ripple factor, depth of density modulation, and decentred parameter on self-focusing and self-trapping is analysed and discussed both analytically and numerically.
关键词： self-focusing,Hermite cosh Gaussian beam,self-trapping,relativistic non-linearity
更新于2025-09-19 17:13:59
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Relativistic Self-Focusing of Hermite-cosh-Gaussian Laser Beam in Magnetoplasma with Exponential Plasma Density Ramp
摘要： In the present manuscript, we analyse the effect of exponential plasma density ramp for relativistic self-focusing of Hermite-cosh-Gaussian laser pulse in magnetoplasma. The exponential plasma density ramp is found to be more prominent in achieving the stronger self-focusing of Hermite-cosh-Gaussian laser beam in comparison to the tangential plasma density ramp. We propose a theoretical model for propagation of Hermite-cosh-Gaussian laser pulse in magnetoplasma with exponential density ramp. The nonlinearity in the medium arises because of the relativistic motion of electrons, being responsible for relativistic self-focusing. Equation of the beam width parameter is set up by taking the expression for the dielectric function and following Wentzel-Kramers-Brillouin (WKB) with paraxial ray approximations for mode indices m = 0, 1 and 2. Effect of decentered parameter is also analysed, which results in stronger self-focusing of the Hermite-cosh-Gaussian laser beam. Stronger self-focusing of laser beam is more pronounced in high density plasma with higher magnetic field.
关键词： self-focusing,decentered parameter,Hermite-cosh-Gaussian beam,exponential density ramp
更新于2025-09-19 17:13:59
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Plasma eyepieces for petawatt class lasers
摘要： Focusing petawatt class laser beams to a variety of spot sizes for different applications is expensive in cost, labor, and space. In this paper, we propose a plasma lens to flexibly resize the laser beam by utilizing the self-focusing effect of laser in plasmas. Using a fixed conventional focusing system to focus the laser a short distance in front of the plasma, we can adjust the effective laser beam waist within a certain range, with the plasma lens acting as an adjustable eyepiece in a telescope. Such a setup is a powerful tool for laser wakefield accelerator experiments in state-of-the-art petawatt laser projects and allows for scanning focal spot parameters.
关键词： self-focusing effect,plasma lens,laser wakefield acceleration,petawatt lasers,adjustable eyepiece
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Toroidal and reverse flux of light in the sharp focus
摘要： We obtain a set of explicit analytical expressions that completely describe a light field with a double higher-order singularity (phase and polarization), as well as distributions of its intensity and energy flux near the focus.There is a reverse energy flux on the optical axis near the focus, which is comparable in magnitude with the forward flux. There is a toroidal energy flux in the focal area near the dark rings in the distribution of the longitudinal component of the Poynting vector.
关键词： cylindrical vector beam,optical vortex,energy backflow,toroidal vortex,tight focusing
更新于2025-09-19 17:13:59
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Hadron Therapy Based on Laser Acceleration in the Plasma Channel Using Oxygen Ionization
摘要： In a cancer radiation treatment, Hadron therapy plays an important role as a technique with a high accuracy providing treatment results better than conventional radiation therapy methods such as chemotherapy. The laser-based Hadron therapy techniques are attractive due to their compactness in producing miniaturized particle accelerators and supporting a more intense electric field compared to other methods. A good-quality laser beam focusing and guiding in a cold plasma channel leads to an accurate and precise laser spot after focus, which is an important necessity in medical aims and occurs in ????-wavelength (ultra-short pulse) laser types. A method used to level up this treatment approach has been emerged by using high-power lasers along with plasma channels as a source for high energy to more effectively perform the Hadron therapy. Additionally, cancer treatment by using ions as the particle transferor is preferred over other methods for Hadron therapy due to some physical properties such as maximum energy deposition to the cancerous targets providing a better dose delivery to the tumor. In this paper, multiple simulations around the dose delivery procedures were presented for efficient dosimetric evaluations. Moreover, the effects of the electric field on the particle energy enhancement were evaluated in the presence of the plasma channel. Finally, it was demonstrated that the use of Oxygen ion in the presence of plasma channel is the appropriate approach due to its minor energy dissipation through matter on the way to the tumor for a better dose delivery which was impressed with radially polarized laser accelerator simultaneously. The proposed research demonstrated that the Hadrons can reach the maximum accelerated energy and convey the maximum path through the body to the cancerous target and finally deliver the sufficient dose to the tumor by using Oxygen ion beam in a cold plasma channel, which is low in density, with appropriate laser power. Consequently, Hadron therapy by using Oxygen ionization in the laser-plasma based accelerator is an impressive and efficient method for precise cancer treatment. Lastly, Laser-Plasma accelerators have three important limitation factors of “Energy Spread”, “Dephasing Length”, and “Pump Depletion”, which can limit the energy increasing. In this paper, facing up to these limitations was a critical challenge in Hadron therapy for better Hadron acceleration and dose delivery.
关键词： Beam Focusing,Hadron Therapy,Oxygen Ionization,Plasma Channel,Laser Acceleration,Cancer Radiation Therapy,Pump Depletion,Dephasing Length,Energy Spread
更新于2025-09-16 10:30:52
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On the Mechanism of Absorption and Restoration of Radiation Transmission in the Channel of Small-Scale Self-Focusing of a Short Laser Pulse in Neodymium Glass
摘要： When diagnosing a small-scale self-focusing (SSSF) channel of a 0.5-ns laser pulse with an intensity of 3–5 GW/cm2 in neodymium glasses, an absorption jump was detected (with a front of ≈0.5 ns) at wavelengths of 1.06 and 0.66 μ m in addition to filament-like damage typical of SSSF, spectral broadening, and laser radiation scattering. The absorption coefficient reached 0.15 cm–1, and transmission in the medium was restored during 15–35 ns for phosphate glass and 5–10 ns for silicate glass. The physical bases of this effect of the appearance and relaxation of absorption in glasses have not been previously presented. An analysis of the experimental data showed that the absorption jump is due to the fast population of the 4I11/2 level of Nd3+ ions in glasses when nonlinear processes occur in the SSSF channel such as stimulated Raman scattering and broadening of the laser pulse spectrum. The relaxation time of the population at the 4I11/2 level and the restoration of transmission in glasses after the termination of the laser pulse are determined by the characteristic sizes of the Nd3+ ions excitation regions arising in the samples upon interference of the laser and scattered radiation, as well as the thermophysical characteristics of the glasses.
关键词： self-focusing,neodymium glass,powerful laser pulse,induced absorption
更新于2025-09-16 10:30:52
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HIGH GAIN SLOTTED WAVEGUIDE ANTENNA BASED ON BEAM FOCUSING USING ELECTRICALLY SPLIT RING RESONATOR METASURFACE EMPLOYING NEGATIVE REFRACTIVE INDEX MEDIUM
摘要： In this paper, a new high performance slotted waveguide antenna incorporated with negative refractive index metamaterial structure is proposed, designed and experimentally demonstrated. The metamaterial structure is constructed from a multilayer two-directional structure of electrically split ring resonator which exhibits negative refractive index in direction of the radiated wave propagation when it is placed in front of the slotted waveguide antenna. As a result, the radiation beams of the slotted waveguide antenna are focused in both E and H planes, and hence the directivity and the gain are improved, while the beam area is reduced. The proposed antenna and the metamaterial structure operating at 10 GHz are designed, optimized and numerically simulated by using CST software. The e?ective parameters of the eSRR structure are extracted by Nicolson Ross Weir (NRW) algorithm from the s-parameters. For experimental veri?cation, a proposed antenna operating at 10 GHz is fabricated using both wet etching microwave integrated circuit technique (for the metamaterial structure) and milling technique (for the slotted waveguide antenna). The measurements are carried out in an anechoic chamber. The measured results show that the E plane gain of the proposed slotted waveguide antenna is improved from 6.5 dB to 11 dB as compared to the conventional slotted waveguide antenna. Also, the E plane beamwidth is reduced from 94.1 degrees to about 50 degrees. The antenna return loss and bandwidth are slightly changed. Furthermore, the proposed antenna o?ered easier fabrication processes with a high gain than the horn antenna, particularly if the proposed antenna is scaled down in dimensionality to work in the THz regime.
关键词： negative refractive index,slotted waveguide antenna,metamaterial,beam focusing,high gain,electrically split ring resonator
更新于2025-09-16 10:30:52
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Second harmonic generation of high power laser beam in cold quantum plasma
摘要： Second harmonic generation of high power laser beam in cold quantum plasma (CQP) is investigated in present communication. In order to derive 2nd order differential equations governing the behavior of laser beam against normalized distance, paraxial theory and WKB approximation are adopted. There is self-focusing of beam on account of relativistic increase in mass of electron, which further results in production of intensity gradients in transverse direction. The electron plasma wave (EPW) gets excited due to these intensity gradients at pump wave frequency. Further, there is an interaction of EPW with pump beam thereby producing second harmonics. In order to study the effect of various parameters of laser and plasma medium on self-focusing of pump beam and second harmonic yield, we have carried out numerical simulations. The comparison of present results is made with classical relativistic plasma (CRP).
关键词： Second harmonic yield,Cold quantum plasma,Electron plasma wave,Self-Focusing
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Comparison of SC Fibers for fs Ti:Sapphire Based Hyperspectral CARS Microscopy
摘要： Hyperspectral coherent anti-Stokes Raman scattering (CARS) microscopy is a rapidly developing field enabling label-free, chemically selective bio-imaging based on Raman signatures. A significant factor limiting its clinical application is the complexity of current laser sources. A solution immediately relevant to two-photon excited fluorescence imaging laboratories is coherently broadening a fs Ti:Sapphire laser seed in a fiber to provide the Raman wavelengths via spectral-focusing (SF) CARS. The NKT fiber with two Zero Dispersion Wavelengths (ZDWs) is one option but the spectrum exhibits low Power Spectral Density (PSD) because of the large (>800 nm) spectral broadening. Here we perform the first systematic comparison sweeping (i) input pump power, (ii) pump wavelength and (iii) fiber length comparing the coherent SC from a femtoWHITE-CARS (2 ZDWs) fiber, a fiber with one ZDW offset above the seed wavelength, and an all-normal dispersion (ANDi) fiber. Starting with the seed laser polarisation aligned to a principal fiber axis, we show the total experimentally measured spectral output and importantly the polarisation resolved spectral component on the orthogonal axis, which is a measure of the nonlinear power-dependent depolarisation. This orthogonal component will degrade the efficiency of the CARS signal but still contributes to the bio-toxicity that limits the maximum power for imaging. Finally, we show representative SF-CARS microscopy images to showcase the power of this technique.
关键词： fiber optics,spectral-focusing,Ti:Sapphire laser,Hyperspectral CARS microscopy,supercontinuum generation
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Zhenjiang, China (2019.8.4-2019.8.8)] 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Imaging Analysis of Micro-milling Tool in the Process of Tool Setting Based on Digital Holography
摘要： In the process of ultra-precision machining, the tool-setting accuracy of the micro-milling tool is limited by the tool diameter. The accuracy of tool setting decreases with the decrease of tool diameter, which becomes an important factor for restricting the accuracy of ultra-precision machining. Based on the imaging principle of digital in-line holography, an efficient and non-contacted method for tool setting was proposed for improving the accuracy of tool setting. Aiming at the imaging problem of micro-milling tool, the evaluation function based on wavelet transform was introduced in the process of progressive search, so the optimal reconstructed image was accurately obtained through the autofocusing algorithm. Then the zero-order term and the conjugate image were eliminated via the self-snake diffusion. The tool contour was extracted by Sobel operator, and tool diameter was measured using different methods. Measurement results proved that holographic imaging can meet the requirements of in-position dynamic measurement for micro-milling tools, and also provided an important basis for the accuracy of tool setting.
关键词： tool setting,auto-focusing,digital holography
更新于2025-09-16 10:30:52