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- 摘要
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Study of multi-function electron gun based on CNTs cathode
摘要： A multi-function electron gun is demonstrated in this work. Through the grid type focusing electrode of the electron gun, the electron gun integrates the function of vacuum measurement. The simulation results reveal that the electron gun has ability to focus the electron beam. And its vacuum measurement range is from 10-6 to 10-3 Pa. The multi-function electron gun has practical application value in small scale vacuum electronic devices.
关键词： multi-function,vacuum measurement,focusing,electron gun
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities
摘要： Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray intensity,X-ray spectrum,focusing,electron acceleration,electron emission,Lithium Tantalate
更新于2025-09-23 15:21:21
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Relativistic Self Focusing and Frequency Shift of super-Gaussian Laser Beam in Plasma
摘要： Relativistic self focusing and frequency shift of laser beam having super-Gaussian profile in space and Gaussian profile in time is studied in a plasma. The relativistic mass nonlinearity is found to cause time dependent self focusing of the laser pulse and the saturation effect of nonlinearity avoids point focusing of the beam. For ultrashort laser pulse, the front of the pulse undergoes frequency down shift while that of the tail undergoes up shift. Frequency shift increases and self focusing becomes stronger for higher intensity of the laser. The self focusing is also stronger for the laser beam carrying larger wavelength.
关键词： Beam width parameter,Self focusing,Frequency shift,super-Gaussian laser,Moment Theory,Relativistic nonlinearity
更新于2025-09-23 15:21:01
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Self-focusing of UV radiation in 1 mm scale plasma in a deep ablative crater produced by 100 ns, 1 GW KrF laser pulse in the context of ICF
摘要： Experiments at the GARPUN KrF laser facility and 2D simulations using the NUTCY code were performed to study the irradiation of metal and polymethyl methacrylate (PMMA) targets by 100 ns UV pulses at intensities up to 5 3 1012 W cm?2. In both targets, a deep crater of length 1 mm was produced owing to the 2D geometry of the supersonic propagation of the ablation front in condensed matter that was pushed sideways by a conical shock wave. Small-scale ?lamentation of the laser beam caused by thermal self-focusing of radiation in the crater-con?ned plasma was evidenced by the presence of a microcrater relief on the bottom of the main crater. In translucent PMMA, with a penetration depth for UV light of several hundred micrometers, a long narrow channel of length 1 mm and diameter 30 μm was observed emerging from the crater vertex. Similar channels with a length-to-diameter aspect ratio of ～1000 were produced by a repeated-pulse KrF laser in PMMA and fused silica glass at an intensity of ～109 W cm?2. This channel formation is attributed to the effects of radiation self-focusing in the plasma and Kerr self-focusing in a partially transparent target material after shallow-angle re?ection by the crater wall. Experimental modeling of the initial stage of inertial con?nement fusion-scale direct-drive KrF laser interaction with subcritical coronal plasmas from spherical and cone-type targets using crater-con?ned plasmas seems to be feasible with increased laser intensity above 1014 W cm?2.
关键词： fused silica glass,UV radiation,PMMA,KrF laser,plasma,ICF,self-focusing
更新于2025-09-23 15:21:01
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Self-focused amplitude modulated super Gaussian laser beam in plasma and THz radiation with high efficiency
摘要： Based on self- focusing of an amplitude modulated super Gaussian laser beam in preformed ripple density plasma, one scheme can be proposed for generating terahertz (THz) radiation at the modulation frequency when pondermotive nonlinearity is operative. The eikonal in paraxial ray approximation (PRA) along with higher order terms in the expansion of the dielectric function have been taken into account. Intensity variation in the direction transverse to the propagated laser causes a pondermotive force which generates transient transverse nonlinear current. At the modulation frequency, the mentioned current drives radiation in THz domain. Therefore, comparing to simple PRA, inclusion of terms with higher order enhances beam self-focusing, THz radiation field and, efficiency. In addition, the degree of the self-focusing is reduced in higher laser beam orders and has changed by the modulation index and the time. Here, by considering higher order paraxial ray approximation and optimizing laser beam and ripple density, plasma parameters are investigated and the efficiency of THz radiation reaches up to 6.5%. This method can be applied for the efficient types of THz radiation.
关键词： Efficiency,Self-focusing,Terahertz radiation,Super Gaussian beam,Amplitude modulated
更新于2025-09-23 15:21:01
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Semiclassical theory of laser-assisted radiative recombination
摘要： We study the process of laser-assisted radiative recombination of an electron with a proton by using a semiclassical approach involving calculation of classical trajectories in combined laser and Coulomb fields. Due to chaotic scattering in the combined fields, the radiation probability as a function of the impact parameter and the constant phase of the laser field exhibits chaotic behavior and fractal structures. We obtain a strong enhancement of the recombination cross section as compared to the laser-free case due to the Coulomb focusing effect. For sufficiently low incident electron velocities the cross section becomes infinite, and we limit it by assuming a finite laser pulse duration. With the pulse duration tp = 5 ps we obtain the gain factor for capture into the ground state of the hydrogen atom of about 220 for infrared fields in the intensity range 109–1012 W/cm2. The gain factor grows with tp but slower than linearly.
关键词： chaotic scattering,fractal structures,semiclassical approach,Coulomb focusing effect,laser-assisted radiative recombination
更新于2025-09-23 15:21:01
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Control of Multiple Filamentation of Femtosecond Laser Pulses in Air
摘要： The results are presented of experiments on controlling the characteristics of the multiple filamentation domain of femtosecond laser pulses along atmospheric paths via variations in the initial spatial focusing, beam radius, and pulse energy, as well as the optical field structure at the initial beam aperture.
关键词： filamentation,femtosecond pulse,bimorph deformable mirror,laser radiation,postfilamentation light channel,self-focusing
更新于2025-09-23 15:21:01
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PERFORMANCE IMPROVEMENT OF PATCH ANTENNA USING CIRCULAR SPLIT RING RESONATORS AND THIN WIRES EMPLOYING METAMATERIALS LENS
摘要： In this paper, the left-handed metamaterial which acts as a lens is employed to improve the performance of a microstrip patch antenna. The left-handed metamaterial used in this work is a three-dimensional periodic structure which consists of circular split ring resonators and thin wires. The three-dimensional periodic metamaterial structure shows angular independency characteristics in wide range angles, so it acts as a metamaterial lens. However, the MTM structure in?nite periodicity truncation has no impacts on the MTM lens scattering, e?ective parameters and homogeneity. The left-handed metamaterial is placed in front of the microstrip patch antenna and due to the negative refractive index property of the left-handed metamaterial; the radiated electromagnetic beam size decreases which results in a highly focused beam. The proposed antenna has been designed and simulated using CST microwave studio, and the metamaterial e?ective parameters are extracted from the S parameters by using Nicolson-Ross-Weir algorithm and by selecting the appropriate ambiguity branch parameter. Furthermore, the angular independency of the metamaterial lens has been veri?ed by rotating the metamaterial structure with respect to the excitation probe of the transverse electromagnetic waves and extracting the S-parameters and the e?ective parameters for each rotation angle. A parametric analysis has been performed to study the e?ects of the patch antenna and left-handed metamaterial lens separation and the size of the three-dimensional left-handed metamaterial structure on the radiating properties and the impedance matching of the proposed antenna. For the experimental veri?cation, the proposed antenna operating at 10 GHz is fabricated; the return loss, radiation pattern and gain for the proposed antenna with and without metamaterial are measured. Furthermore, the results show that the antenna gain is improved by 4.6 dB which validates the concept of beam focusing using negative refractive index metamaterial structure, while the return loss and bandwidth are slightly reduced. The simulation and experiment investigated the idea of the beam focusing using negative refractive index metamaterial lens in microwave regime.
关键词： microstrip patch antenna,CST microwave studio,beam focusing,Nicolson-Ross-Weir algorithm,parametric analysis,left-handed metamaterial,circular split ring resonators,negative refractive index,angular independency,experimental verification,thin wires
更新于2025-09-23 15:21:01
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Nonlinear Optics || Processes Resulting from the Intensity-Dependent Refractive Index
摘要： In this chapter, we explore several processes of practical importance that occur as a result of the intensity-dependent refractive index.
关键词： refractive index,self-trapping,laser beam breakup,self-focusing,nonlinear optics
更新于2025-09-23 15:21:01
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Rapid Size-Focusing of Gold Nanoclusters with an Oxidant
摘要： Rapid size-focusing of gold nanoclusters can be achieved by the addition of K3[Fe(CN)]6. The conditions for this have been optimized, and the possible role that it plays proposed.
关键词： Gold,Oxidant,Size-focusing,Nanocluster
更新于2025-09-23 15:21:01