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Electromagnetic waves' self-focusing in metamaterials having both LHM and RHM behavior: an application to filter design
摘要： Self-focusing, also known as Talbot’s effect had been widely studied by the scientific community. In this paper we show self-focusing as a coherence propagation phenomenon, in particular we studied self-focusing for a pulse propagating in a metamaterial with both behaviors: left handed material (LHM) and right handed material (RHM). These dual behaviors allow the construction of frequency filters in the range of frequency in which the metamaterial stops behaving as a LHM (negative refraction index) and begins an RHM behavior (positive refraction index). The coherence length (CL) for pulses propagating in these metamaterials seems to be larger when its frequencies are in the LHM region. Finally, we show that the cell’s size turns out to be critical in designing the filter, and as an example we present here four metamaterial cells.
关键词： metamaterials,filters,self-focusing,Coherence propagation
更新于2025-09-23 15:23:52
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Controlling the relativistic self-focusing of Hermite-cosh-Gaussian beams in plasma
摘要： The purpose of current study was to find the effects of Hermite-cosh-Gaussian (HChG) beam characteristics on the relativistic self-focusing. The Self-focusing Parameter (SFP), for mode indexes of m=0, 1, and 2 is proposed which provides a basis for achieving the nonlinear self-focusing dependencies on the beam characteristics. The dissimilar nonlinear self-focusing dependencies of different mode indexes on the initial intensity and decentered parameter of HChG beam are founded. The predictions of SFP model are then validated by investigating the beam focusing/diverging along the propagation axis and the exact conformity is observed. The results of introduced model can by applied for HChG beams with higher mode indexes, the Hermite Gaussian and cosh-Gaussian beams.
关键词： Hermite-cosh-Gaussian beam,mode indices,Decentered parameter,Plasma,Relativistic self-focusing
更新于2025-09-23 15:23:52
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Method for Processing and Analysis of the Images of a Network of Thermal Fatigue Cracks on the Surfaces of Rollers of Continuous Casting Machines
摘要： We propose an algorithm for the analysis of thermal fatigue cracks on the surfaces of rollers of continuous casting machines that does not require adaptation to images of various types and individual choice of parameters. For this purpose, the images are analyzed for a sufficiently large subset of the sets of values of the parameters. The result of this classification is regarded as a fuzzy set with a membership function of each element equal to the number of sets of parameters responsible for the detection of this element as a component of the frame of the damage grid.
关键词： image processing,thermal fatigue cracks,self-focusing,fuzzy sets,classification
更新于2025-09-23 15:21:21
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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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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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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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Effect of obliquely external magnetic field on the intense laser pulse propagating in plasma medium
摘要： In this paper, self-focusing of intense laser pulse propagating along the obliquely external magnetic field on the collisional magnetoactive plasma by using the perturbation theory have been studied. The wave equation describing the interaction of intense laser pulse with collisional magnetoactive plasma is derived. In addition, employing source-dependent expansion (SDE) method, the analysis of the laser spot-size is discussed. It is shown that with increasing of the angle in obliquely external magnetic field, the spot-size of laser pulse decreases and as a result laser pulse becomes more focused. Furthermore, it is concluded that the self-focusing quality of the laser pulse has been enhanced due to the presence of obliquely external magnetic field in the collisional magnetoactive plasma. Besides, it is seen that with increasing of ν/?0, the laser spot-size reduces and subsequently the self-focusing of the laser pulse in plasma enhances. Moreover, it is found that changing the collision effect in the magnetoactive plasma leads to increases of self-focusing properties.
关键词： obliquely external magnetic field,Collisional magnetoactive plasma,source-dependent expansion method,laser spot-size,self-focusing
更新于2025-09-23 15:19:57
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Self-focusing of multi-Gaussian laser beams in nonlinear optical media as a Keplera??s central force problem
摘要： In this paper self-focusing of multi-Gaussian laser beam in nonlinear optical media has been investigated theoretically. Saturation of the optical nonlinearity has been incorporated through cubic-quintic model. Moment theory approach in W.K.B approximation has been invoked to find the numerical solution of nonlinear wave equation for the field of incident laser beam. Particularly the dynamical evolutions of the beam width of the laser beam with distance of propagation have been investigated in detail. It has been shown that the self-focusing of the laser beam resembles to Kepler’s central force problem.
关键词： Potential well,Self focusing,Kepler’s central force problem,Multi Gaussian
更新于2025-09-23 15:19:57