On the effect of absorption on multiple wave-scattering in a magnetized turbulent plasma

Multiple scattering of electromagnetic waves by a plane layer of a turbulent magnetized collision plasma is considered. The influence of the distance between both the emitter and the receiver and the layer boundaries is analysed. It is found that the width of the angular spectrum of the received radiation for sufficiently strong absorption in the plasma is greater than in the collisionless plasma; the spectral maximum is substantially displaced with respect to the direction of the source. It is shown that these effects are weakened when the emitter approaches the layer. The relationship between the spectral width and also the displacement of its maximum and the distance from the receiver to the layer boundary may be substantially non-monotonic.     

Statistical characteristics of radiation of a point source scattered by a layer of turbulent collisional magnetized plasma

We consider multiple scattering of electromagnetic waves by a layer of turbulent magnetized collisional plasma. The influence of the distances from the layer's boundaries to the emitter and receiver is analyzed. We find out that, provided absorption in the plasma is strong enough, the width of the angular spectrum of the received radiation can be larger than in the collisionless plasma, and the maximum of the spectrum is substantially shifted with respect to the direction to the source. It is shown that these effects weaken as the emitter approaches the layer. The dependence of the width of the spectrum and the shift of its maximum on distance from the receiver to the layer's boundary can be substantially nonmonotonic. Lobachevsky State University, Nizhny Novgorod, Russia; Georgian Technical University, Tbilisi, Georgia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol.42, No. 4, pp. 340–354, April 1999.     

斜程大气中聚焦J0相关部分相干光束的传输特性

采用部分相干光交叉谱密度理论,给出了适用于任意大气湍流条件的斜程湍流大气传输J₀相关部分相干光束在接收面内的长期平均光强分布、光束长期扩展和质量因子的解析表达式,分析了天顶角、传输距离、光源相干性以及湍流外尺度对接收面光强分布特性和光束扩展的影响.研究结果表明：在天顶角和传输距离一定的条件下,通过选择合适的光源相干性可控制焦面光强为平顶分布或中心光强为最大;在传输距离给定的条件下,随着天顶角或大气湍流外尺度的增加,焦斑光强分布均由中央凹陷分布逐渐变为高斯分布.焦面附近光强的中央凹陷比焦面的中央凹陷浅.J₀相关部分相干光束实际焦斑位置随天顶角、湍流外尺度的增加以及相干性减弱而移向发射端. 关键词： 部分相干束 大气湍流 0相关')" href="#">J₀相关 斜程传输     

声速测量实验中界面反射问题的探讨

探讨在声速测量实验中,声波在发射器和接收器两个端面之间反向形成极大值的位置和条件,以及声波强度随距离变化的规律。这有利于学生正确实验和理解声波特性。     

Current in a high-current planar diode with a discrete emitting surface

The dependence of the current on emitter size is obtained for a high-current planar diode with a discrete emitting surface. It is shown that if the distance between the emitters appreciably exceeds their size, the dependence of the current on the ratio of the emitter size to the diode gap is a power dependence with an exponent of 3/2. The voltage dependence of the current obeys the “three-halves” law up to higher voltages than that for a planar diode with a homogeneous emitting surface. Zh. Tekh. Fiz. 69, 97–101 (June 1999)     

Pulse properties of an electronic emitter with a plasma limited by a boundary ionic layer

Results of the investigation of the pulse control of an electronic emitter with a plasma limited to a boundary ionic layer are presented. The control of the emitter current was realized by modulating the plasma area by means of varying the extent of the ionic layer in the emission channel. It is shown that the time for the formation of the front and trailing edge of the current pulse depends on the time for establishing a stationary distribution of ions in the boundary layer. For an electronic emitter, based on a reflective discharge with a field cathode, this time is of about 10^–8 sec. The experimental setup is described, and the results obtained in the pulse control of an emitter current through modulation of the emission area are presented.Institute of Automated Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 28–33, May, 1992.     

驻波法测量声速实验的讨论

根据声波在2个换能器之间多次反射和声波在空气中的衰减,研究了驻波法测量声速实验中接收器输出信号随接收器到发送器间距离的变化.理论推导结果表明:声波在一般情况下不是严格的驻波,但是当反射比接近-1时则是双曲函数形式的驻波,这与实验测量结果一致.只有接收器到发送器的距离比较远,反射比接近-1时,才能得到几乎理想的驻波.     

1.3μm场助TE光阴极In1-xGaxAsyP1-y/InP的能带计算及外延层的设计

本文首先简述了1.3μm场助TE光阴极InP(衬底)/In_1-xGa_xAs_yP_1-y(光吸收层)/InP(发射层)/Ag/CsO的工作原理,并对其能带结构进行了计算,得到了In_1-xGa_xAs_yP_1-y(光吸收层)/InP(发射层)的势垒高度、掺杂、InP发射层厚度、组份、渐变区宽度,偏压及耗尽层宽度间的定量关系。并由此出发,对光阴极各参数的设计进行了分析讨论。     

Investigations on power penalty at different spectral width using small signal analysis with higher-order dispersion

In this paper, a modified small signal analysis for power penalty at different spectral width of the light source has been investigated by incorporating the higher-order dispersion parameters. Further, we have analyzed the individual and combined effects of second- and third-order dispersion parameter on power penalty at different spectral line widths. The results have been reported over the range of 10-1000 km by considering the impact of individual and the combined higher-order dispersion terms. It has been observed that by reducing the spectral line width of the light source, the power required at the receiver can be minimized. The power penalty is further reduced if only third-order dispersion parameter is considered. Further, the transmitter distance can be maximized if the spectral width of the light reduces to 100 kHz.     

On the transverse distribution of a resonance field excited by a Gaussian electromagnetic beam on the critical surface of a radially nonuniform plasma sphere

The transverse distribution of the resonance field excited by a Gaussian electromagnetic field on the critical surface of a radially nonuniform plasma sphere is studied. Analytical expressions are obtained for this distribution. It is shown that when a laser beam is focused in front of or behind a spherical target, identical values of the integrated resonance coefficient can correspond to substantially different (in width) distributions of the resonance field over the spherical critical surface. Zh. Tekh. Fiz. 67, 125–128 (October 1997)     

Spectroscopic Investigation of a Double Discharge Pulsed Electron Beam Generator

ABSTRACT

The wide range of applications of the plasma-based electron beam generator make it necessary to diagnose the device with a noninterfering method. The results of experimental and modeling studies of neutral helium and hydrogen beta spectral lines emitted from the double discharge pulsed electron beam generator are presented in this paper. Neutral helium lines emitted from the plasma in the pressure range 0.1–0.4 torr are studied and compared with results of the collisional radiative model. The duration of the electron beam is shorter than 100 ns, and the peak current intensity is of order amperes. The full width at half maximum of the H _β spectral line is used for the determination of the plasma electron density, found as 3.16 × 10²¹ m^?3 at 0.3 torr, and good agreement is obtained by comparing with the full computer simulation method.     

谱合成光束特性的模拟分析

建立了光束谱合成的传输模型.应用光线追迹方法，将闪耀光栅引起的相位变化用槽间光程差和槽内光程差来表示，建立了光束倾斜入射到光栅时相位变化的计算模型.利用衍射积分方法，给出了阵列光源各子光束经谱合成系统后输出光场的解析表达式.依据光束非相干叠加的原理，计算得到合成光束的光强分布.在此基础上，利用强度二阶矩方法，分别计算了阵列光束和合成光束的M²因子，并定量分析了谱合成系统参数对合成光束特性的影响.研究结果表明：通过谱合成系统合成光束的M²关键词： 光束谱合成 阵列光源 闪耀光栅 光束质量     

Micro-scale Fabry–Perot interferometer with high spectral resolution and tunable transmission frequency via chiral waveguide-emitter coupling

A micro-scale Fabry–Perot interferometer with high spectral resolution and tunable transmission frequency is proposed. In this scheme, two partially reflecting mirrors with a separation of several wavelengths is fabricated in a waveguide, and a two-level emitter is located between the mirrors and coupled to the waveguide with chiral interaction. We analytically show that the single emitter plays the role of a strongly dispersive medium and the full width at half maximum (FWHM) of the transmission fringes around the resonance frequency of the emitter can be narrowed by 5 orders of magnitude. The proposed micro-scale interferometer can have the same spectral resolution as meter-scale traditional interferometers. We also show that the central frequency of the narrowed transmission fringe can be tuned by adjusting the asymmetry of the emitter-waveguide coupling. Our scheme has potential applications in the fields of integrated optical circuit and quantum information processing.     

Radiative and non-radiative decay of a single molecule close to a metallic nanoparticle

We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the aim to clarify the distance dependence of the radiative and non-radiative decay rates. We derive analytical formulas based on a dipole-dipole model, and show that the non-radiative decay rate follows a R⁻⁶ dependence at short distance, where R is the distance between the emitter and the center of the nanoparticle, as in Förster’s energy transfer. The distance dependence of the radiative decay rate is more subtle. It is chiefly dominated by a R⁻³ dependence, a R⁻⁶ dependence being visible at plasmon resonance. The latter is a consequence of radiative damping in the effective dipole polarizability of the nanoparticle. The different distance behavior of the radiative and non-radiative decay rates implies that the apparent quantum yield always vanishes at short distance. Moreover, non-radiative decay is strongly enhanced when the emitter radiates at the plasmon-resonance frequency of the nanoparticle.     

Photostimulated diffusion of Na atoms in the alloy NaAu. II. Spectral and polarization dependences

The results of an investigation of the spectral and polarization dependences of the photostimulated diffusion of sodium in heated gold are presented. It is shown that the light-induced increase in the diffusion rate is associated with optical excitation of the electronic structure of the alloy NaAu, which forms in the subsurface layer of gold during the adsorption of the alkalimetal atoms. The semiconductor properties of this alloy are revealed, and the gap width is estimated. Zh. Tekh. Fiz. 68, 108–111 (October 1998)     

Persistent spectral hole-burning in a -doped aluminosilicate glass from 8 to 295 K: Study of the burning and refilling kinetics, and of optical dephasing

High-temperature persistent spectral hole-burning (PSHB), up to room temperature, has been observed in a Eu ³⁺ -doped aluminosilicate glass using a high peak-power nanosecond dye laser. Spontaneous refilling as well as thermal cycling measurements show that at least two mechanisms, a fast and a slow one, are involved in our sample. We suggest that the fast or “easy” component may correspond to a non-photochemical local rearrangement of the host or to photoreduction of the Eu ³⁺ ions and that the second one leading to very stable photoproducts may correspond to transfer of an electron over a sizable distance through a several-step process. The mechanisms we suggest agree with light-induced hole refilling measurements. Line broadening mechanisms are discussed and the temperature-dependent part of the homogeneous width and of the spectral shift is interpreted in terms of a two-phonon (Raman) process involving pseudo-local phonons. Received 28 July 1999     

Complex order fractional Fourier transforms and their use in diffraction theory. Application to optical resonators

The electromagnetic field transfer by diffraction from a spherical emitter to a spherical receiver is expressed by a fractional Fourier transform whose order depends on the distance between the emitter and the receiver and their curvature radii. Special attention is paid to complex order transforms: scaled variables and scaled field amplitudes are defined by complying with mathematical consistency. For a given distance of observation, a simple geometrical condition is set up to determine whether the corresponding transform order is a real or a complex number. The result is applied to check the stability of optical resonators.     

Influence of nonlinear effects on whistler emission in magnetoactive plasma

The influence of thermal and strictional nonlinear effects on the whistler emission in magnetoactive plasma is studied experimentally. It is established that a nonlocal thermal nonlinearity determines the directional pattern of the antenna, while a strictional nonlinearity, which is strongest near the antenna surface, is responsible for the matching of the emitter with the surrounding plasma. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 548–551 (25 April 1998)     

Interference simulation in a cold collisionless moving magnetized plasma slab and (free surface of plasma slab)

Abstract

The pattern of intensity due to the interference in a cold collisionless magnetized moving plasma slab is investigated. Theoretically, it is assumed the mentioned layer has been located as a thin layer in an etalon Fabry–Perot interferometer surrounded by vacuum. The direction of external magnetic field is normal to the plasma surface and the plasma slab moves parallel with external constant magnetic field. By taking into account the relativistic considerations, the functions of transmitted intensity are presented coincident with the Airy function form in laboratory and plasma slab frames, respectively. The effects of plasma frequency, cyclotron frequency, thickness of plasma slab, and velocity of the plasma slab on band width, finesse factor, and visibility are simulated. Finally with the assumption that there are two wavelengths near together in incident electromagnetic beam the power resolution for this configuration are analyzed. All studies mentioned above have been done for S-polarized and P-polarized electromagnetic beams separately.     

Propagation of light through an optically thick flat homogeneous cloud layer

Abstract

Monte Carlo simulations of light pulse transfer through a flat homogeneous cloud layer are used to compute zero, first and second moments of the light power temporal distribution at the input of a receiver placed at the cloud bottom or removed from it to a distance H in a pure atmosphere. The upper boundary of a cloud layer is considered to be illuminated by an infinitely extended δ-pulsed light beam. Transmittance of the cloud layer T and radiance angular distribution B(θ) at its bottom (these data define the zero moment or the pulse-response energy under steady illumination W), as well as mean propagation time t¯ and variance (width) (Δt)² of the pulse-response are calculated for cloud optical thicknesses τ=0, …, 50, incidence angle θ₀=0, …, 60°, single scattering albedo ω₀=0.995, …, 1.0 and the receiver view angle 2 β=40° and 90°. Monte Carlo simulation results are compared with well known Rosenberg asymptotic formulae for T and B(θ) as well as with a simple model developed for calculating t¯ and Δt. The comparison reveals high accuracy of all formulae considered for the optical thickness τ>10, …, 15. A simple procedure for computing W, t¯ and Δt parameters for a three-layer medium (cloud/pure atmosphere/sea water) is outlined.