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1.
Specific features of the nonstationary transmission of two pulses exciting biexcitons from the ground state in a thin semiconductor film are studied. It is shown that one of the incident rectangular pulses is totally reflected from the film, whereas the second pulse passes through it as through an absolutely transparent medium. Criteria for appearance of a stationary bistable transmission are determined. 相似文献
2.
The effect of nonlinear properties of a material with a periodic structural cell (three-dimensional spiral) on the specificity of transmission and reflection of elliptically polarized laser pulses normally incident on the metamaterial is studied using the finite-difference time-domain method. An analysis of the hodograph of electric-field strength vector showed that an increase in the peak intensity of a linearly polarized laser pulse incident on a sample leads to an increase in the orthogonal component of the electric-field strength vector in the pulse transmitted through the medium. When pulses containing few electric-field periods are incident on a metamaterial, the latter demonstrates radically different optical properties for right- and left-handed circularly polarized light passing through the medium. It was shown that an increase in the intensity of a right-handed (left-handed) circularly polarized ultrashort pulse, incident on a sample composed of a rather large number of right-handed (left-handed) spirals made of nonlinearmaterial, widens the frequency range within which the incident light is almost entirely reflected from the medium. 相似文献
3.
A scattering scheme to probe the time evolution of femtosecond pulses of a soft X‐ray free‐electron laser (FEL) in a multilayer structure is presented. The response of periodic multilayers (MLs) with low and high absorption and various numbers of bi‐layers to a pulse train of Gaussian‐shaped sub‐pulses is calculated. During the passage of the incident pulse the interaction length increases and the scattering profile changes as a function of the spatial position of the pulse within the sample. Owing to stretching of the reflected pulse compared with the incident pulse, the time‐dependent scattering evolution in the ML can be visualized along a spatial coordinate of a position‐sensitive detector. Using a scattering geometry where the mean energy of the incident pulse train is slightly detuned from the energy of maximum reflectivity at the first‐order peak, the response of the ML shows an oscillator behaviour along this spatial coordinate at the detector. For a FEL wavelength of 6.4 nm this effect is promising for MLs with low absorption, such as La/C for example. On the other hand, the oscillations will not be present for MLs with high absorption. Therefore a low‐absorbing ML is a sensitive tool for studying the possible change of sample absorption caused by femtosecond‐pulse interaction with matter. 相似文献
4.
A numerical experiment in which two relativistically intense laser pulses are normally incident on a layer of a diluted plasma
from two opposite sides is described. The period of Langmuir plasma oscillations is much larger than the pulse duration and
the product of this period by the speed of light is much larger than the thickness of the layer. A pulse propagating to the
right is incident on the layer earlier than the counter pulse and carries a significant fraction of electrons or all of the
electrons from the plasma. Under certain conditions, electrons form a bunch, which contains most of the electrons and has
a thickness much smaller than the wavelength of light. The counter pulse perturbs the motion of the bunch and initiates the
emission of a short few-cycle pulse, which propagates in the positive direction (to the right), significantly differs in structure
from the counter pulse, and has a duration much smaller than the field period in laser pulses. 相似文献
5.
本文运用电火花声源在一厅堂内对胶合板条和钢板网组成的顶棚以及胶合板贴在混凝土墙面上构成的反射板进行了声反射特性的实验研究。在测试人射和反射声脉冲而利用FFT计算声反射传递函数时,讨论了反射脉冲序列截取的长短对该材料反射传递函数的影响。文中还分析了有肋吸声结构声反射传递函数的变化。提供0°、30°、60°反射传递函数的比较。 相似文献
6.
N. N. Rosanov 《Journal of Experimental and Theoretical Physics》2010,111(4):534-540
The Fresnel reflection of radiation pulses with an exponential temporal amplitude profile is analyzed. The conditions for
the relevance of the concept of reflectance at a complex frequency, the imaginary part of which determined the rate of time
variation of the amplitude, are specified. For the radiation pulses under study, we demonstrate a complex resonance, i.e.,
an increase in the magnitude of reflectance for the complex frequency of incident radiation (trailing edge of a pulse) that
approaches the complex frequency of natural oscillations of oscillators in the medium. 相似文献
7.
Wangyang Cai Yingying Tian Lifu Zhang Hairong He Jiajia Zhao Jin Wang 《Annalen der Physik》2020,532(10):2000295
Reflection and refraction of Airy pulses at a moving step refractive-index boundary are investigated. A comb-like reflected spectrum and an Airy-like transmitted spectrum are formed as an Airy pulse crosses a temporal boundary without initial group velocity mismatch or initial central frequency shift. The reflected and refracted pulses are significantly influenced by the location of temporal boundary and time-dependent refractive index change. The energy of each lobe of the comb-like reflected spectra can be controlled by changing the value of decay factor of the Airy pulse. In the case of an Airy pulse with an initial launch frequency shift, the reflected and refracted frequency shifts depend on the dispersion relation of the medium. The results can be used in potential applications involving optical manipulation. 相似文献
8.
It is found theoretically that the temporal profile of a quasimonochromatic electromagnetic pulse is strongly distorted on
reflection from a thin (on the wavelength scale) film of a plasma-like (semiconductor, metallic) medium under plasma-resonance
conditions. It is shown that an incident Gaussian pulse splits with time (completely or partially) into two reflected pulses,
whose amplitudes can be controlled by varying the relationships among the parameters of the incident pulse and the film.
Zh. Tekh. Fiz. 67, 65–68 (June 1997) 相似文献
9.
Interaction between epsilon-near-zero (ENZ) metamaterials and optical pulses is investigated theoretically. A transform between total transmission and total reflection is revealed for the ultrashort pulses incident onto an ENZ slab, which can be controlled by changing the thickness of the slab. Furthermore, the resonance of the ENZ materials leads to a cutoff frequency in spectroscopic response, where longer wavelengths have no chance to propagate through the ENZ materials and are totally reflected. These characteristics enable the ENZ materials to be applied in ultrashort pulse shapers, cutoff filters, and Fabry–Pérot resonators. 相似文献
10.
A. S. Bugaev P. A. Golovinski V. A. Astapenko E. S. Manuylovich 《Doklady Physics》2016,61(11):531-534
The process of reflection and transmission of ultrashort pulses incident normal to a flat plasma layer of finite thickness and on a step barrier is calculated within an exact mathematical approach for various parameters (barrier width and duration and carrier frequency of a corrected Gaussian pulse) of the problem. 相似文献
11.
A. A. Ionin S. I. Kudryashov L. V. Seleznev D. V. Sinitsyn A. F. Bunkin V. N. Lednev S. M. Pershin 《Journal of Experimental and Theoretical Physics》2013,116(3):347-362
The space-time dynamics of thermal melting, subsurface cavitation, spallative ablation, and fragmentation ablation of the silicon surface excited by single IR femtosecond laser pulses is studied by timeresolved optical reflection microscopy. This dynamics is revealed by monitoring picosecond and (sub)nanosecond oscillations of probe pulse reflection, which is modulated by picosecond acoustic reverberations in the dynamically growing surface melt subjected to ablation and having another acoustic impedance, and by optical interference between the probe pulse replicas reflected by the spalled layer surface and the layer retained on the target surface. The acoustic reverberation periods change during the growth and ablation of the surface melt film, which makes it possible to quantitatively estimate the contributions of these processes to the thermal dynamics of the material surface. The results on the thermal dynamics of laser excitation are supported by dynamic measurements of the ablation parameters using noncontact ultrasonic diagnostics, scanning electron microscopy, atomic force microscopy, and optical interference microscopy of the modified regions appearing on the silicon surface after ablation. 相似文献
12.
M. V. Pyatakhin 《Journal of Russian Laser Research》1992,13(5):354-373
A method of solving the diffraction problem for a linear monochromatic emitter with arbitrary electromagnetic pulse (EMP) and arbitrary spaciotemporal dependence of the source is developed for a linear monochromatic emitter. The theory reveals a small-scale modulation of the spectrum and a change of the EMP form during the time of passage of the current pulse through the emitter when the time of passage of the current pulse through the emitter is of the order of the pulse duration and at characteristic wavelengths compatible with the emitter dimensions. The refraction, reflection and absorption of EMP generated in the atmosphere are estimated. 相似文献
13.
This paper describes the pulse displacement technique(PDT) to simultaneously measure particle size and velocity in applications characterized by a large size range and high particle concentration. PDT is based on the detection of scattered refraction and reflection pulses which sweep past a detector at different times as a particle traverses a narrow probe volume. Basic analytical relationships are presented which allow the calculation of the spatial and temporal widths and separations of the reflection and refraction pulse as a function of particle diameter and velocity. Two implementations of PDT are discussed using one or two receivers with two laser sheets having the same or different wavelengths. This paper also discusses several methods to measure particle velocity with PDT, discusses the limitations associated with signal broadening in practical systems, and briefly presents experimental results which show that the temporal separation between the refraction and reflection and reflection pulse maxima is independent of collecting lens f-number from f/3 to f/20 for particle sizes ranging from 250 to 2000 μm. 相似文献
14.
基于啁啾脉冲放大技术的超短脉冲激光系统是提供超快、超强激光的重要途径,具有良好输出波形和高损伤阈值的多层介质膜脉冲宽度压缩光栅是获得高峰值功率脉冲激光的关键. 基于傅里叶谱变换方法和严格模式理论,分析了多层介质膜光栅(MDG)在超短脉冲作用下的光学特性. 结果表明,当MDG的反射带宽小于具有高斯分布的入射脉冲的频谱宽度时,-1级反射脉冲呈非对称高斯分布,其前沿出现振荡,并且-1级反射脉冲能量开始剧烈下降. 讨论了MDG结构参数对其反射带宽的影响. 分析了MDG与超短脉冲作用时的近场光分布,对提高其抗激光损
关键词:
脉冲压缩光栅
傅里叶谱变换
模式理论
损伤阈值 相似文献
15.
16.
理论研究和数值模拟发现入射光和反射光在低密度等离子体中形成的干涉场可以产生深度的等离子体密度调制. 对于中等强度的入射光,譬如1015W/cm2 ,产生密度调制的时间尺度在几十个光周期的范围. 这样的等离子体密度调制可以起类似布拉格反射镜的 作用,使得后面的入射光在临界面以下的区域产生相位反射. 因为密度调制的周期是光在等 离子体中波长的一半,其产生的反射率可以接近100%. 相位反射也可以在不均匀的低密度 等离子体中产生,它可以极大地减少等离子体对光的吸收,因此在惯性约束核聚变中需要考 虑到它的影响.
关键词:
相位反射
密度调制
激光等离子体
粒子模拟 相似文献
17.
The nonlinear, total internal reflection of a laser pulse from an absorbing layer of finite thickness in the presence of a retrodirective mirror has been considered in the framework of the plane-wave approximation. The dynamics of reflection of a pulse from a nonlinear layer has been investigated on the basis of the solution of Maxwell equations for a refracted wave and constitutive equations for a medium with thermal nonlinearity. The numerical solution of the unsteady equations obtained allows one to determine the evolution of the reflectance of a layer. The time evolution of the energy parameters and the shape of the reflected and transmitted pulses has been numerically simulated. 相似文献
18.
A. A. Andreev I. A. Litvinenko K. Yu. Platonov 《Journal of Experimental and Theoretical Physics》1999,89(4):632-639
The possibility that fast electrons can escape in a direction close to the trajectory of a reflected ultrashort laser pulse
at extremely high laser radiation fluxes is examined analytically and numerically. Analytic estimates are made of the feasibility
of forming electron bursts in the plasma and of their subsequent motion. The self-consistent, collisionless motion of a plasma
acted on by specified incident and reflected ultrashort laser pulses is modeled in two dimensions by the particle-in-cell
method. It is shown that a substantial number of electrons located in the subcritical region are gathered into bunches by
the resultant forces and escape to the vacuum in a direction different from the normal to the target surface within a narrow
range of solid angles. This demonstrates the feasibility of laser acceleration of an electron burst during reflection of an
ultrashort laser pulse from a solid target.
Zh. éksp. Teor. Fiz. 116, 1184–1197 (October 1999) 相似文献
19.
Sanjeev Anand Sahu Soniya Chaudhary Brijendra Paswan 《Waves in Random and Complex Media》2019,29(3):435-455
The present paper aims to investigate the reflection and refraction of quasi-longitudinal (qP) waves at the welded interface between rotating piezoelectric and FGPM half-spaces. The equation of motion and constitutive relations for both the media have been used to derive the expressions for reflection and refraction coefficients for various reflected and transmitted waves. Also, the energy ratios (dependent on incident angle) are calculated. Moreover, the sum of all energy ratios is approximately unity at each value of incident angle which ensures that the law of energy conservation at the interface. Moreover, it is observed that the reflection and refraction coefficients of various reflected and transmitted waves depend not only on the incident angle but also on the material constants of the medium, parameters of the electric potential, initial stress as well as rotation parameters of the two media. A particular case has been deduced to validate the present study. This investigation may have possible applications in the areas of signal processing, transduction, frequency shifting (a change in the velocity of surface waves and controlling the selectivity of a filter compensation) of individual devices. 相似文献
20.
Mössbauer radiation from a copper foil doped with57Co is resonantly absorbed in a stationary Be∶57Fe absorber. Experiments were performed with the source immersed in liquid He at 4.2K, He gas from 4.2 to 78 K, and in liquid HeII to 2 K. Radio-frequency current pulses through the source cause large increases in transmission, mainly after the end of the pulse. These increases are associated with heat transfer instabilities (Taconis oscillations) at the He-metal interface. 相似文献