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.     

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

Abstract

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.     

GaP波导型发射器产生频率可调谐太赫兹脉冲

报道了利用脉宽可调的光子晶体光纤飞秒激光放大器抽运矩形波导结构的GaP晶体太赫兹(THz) 发射器产生频率可调谐的超快THz脉冲.非线性晶体中光整流过程产生的THz辐射频率随抽运光脉冲宽度而 变化. GaP波导THz发射器可通过波导的几何尺寸来控制色散,以达到增加有效作用长度和提高输出功率的目的. 不同横截面尺寸的波导型发射器的THz辐射峰值频率随相位匹配条件的改变而改变,加以脉宽调节技术, 可以在大频谱范围获得频谱精细可调的THz脉冲.实验中在1 mm×0.7 mm的波导型THz发射器中获得了 频率可调谐的THz脉冲.提出实现THz辐射频率大范围调谐的GaP波导型阵列发射器的实施方案.     

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.     

Quantization of plasma density irregularities under the action of a powerful electromagnetic wave: The spectrum of upper hybrid oscillations self-consistently trapped in density cavities

We present a theoretical model of the self-localization of the upper hybrid (UH) oscillations in plasma density depletions due to thermal nonlinearities driven by a homogeneous and monochromatic pump electric field. The Bohr-Sommerfeld condition for the trapped UH oscillations demands that the parameters of the density cavity be quantized. The depth and square of the depletion width across the magnetic field is proportional to an integer. The depth of the parabolically shaped cavity is proportional to the square of its width. The characteristic relative value of the density minimum is a few percent and the width is of the order of one meter for the pump wave amplitudes used in the ionospheric F-region experiments. We consider also the parametric decay of primary, localized UH oscillations trapped in the quantized plasma density depletions into secondary UH oscillations and lower-hybrid waves. We calculated the spectrum of the non-linear stabilized secondary UH oscillations which are also self-consistently trapped in the same density cavity. The spectrum of the UH oscillations is consistent with the observed spectrum of the downshifted (DM) and upshifted (UM) maximum in the stimulated electromagnetic emissions (SEE). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 7, pp. 641–650, July 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     

InP阵列波导光栅的误差分析

在InP阵列波导光栅的制作过程中会引入不同的误差,从而影响器件的性能.为了最大限度地控制误差,提高半导体器件性能,本文采用传输函数法对InP基阵列波导光栅的系统误差和随机误差分别进行了分析.从系统误差的模拟结果中可以得到如下结论:深脊型波导的有效折射率n_c平均每偏移+0.000 1,中心波长偏移+0.05nm.相邻阵列波导长度差ΔL每偏移+0.01 μm,中心波长将偏移+0.44 nm.n_c和ΔL仅仅会影响到传输谱中心通道及其他各通道对应的波长,使得传输谱发生整体漂移,而信道间隔及串扰不会改变.罗兰圆半径R偏移不会影响器件的中心通道对应的波长,但会使其它通道对应的波长发生变化,最终使得信道间隔改变,R增加50 μm,信道间隔减小0.03 nm.从随机误差模拟结果中,得出:波导芯区折射率、上包层折射率、衬底折射率、波导宽度和波导芯层厚度的随机波动会对阵列波导光栅的串扰产生较大的影响.根据以上分析,可以通过控制不同参量来调节器件的中心波长以及信道间隔等来优化阵列波导光栅的光学性能.     

Mid-range adiabatic wireless energy transfer via a mediator coil

A technique for efficient mid-range wireless energy transfer between two coils via a mediator coil is proposed. By varying the coil frequencies, three resonances are created: emitter–mediator (EM), mediator–receiver (MR) and emitter–receiver (ER). If the frequency sweeps are adiabatic and such that the EM resonance precedes the MR resonance, the energy flows sequentially along the chain emitter–mediator–receiver. If the MR resonance precedes the EM resonance, then the energy flows directly from the emitter to the receiver via the ER resonance; then the losses from the mediator are suppressed. This technique is robust against noise, resonant constraints and external interferences.     

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.     

Solution of near-field thermal radiation in one-dimensional layered media using dyadic Green's functions and the scattering matrix method

A general algorithm is introduced for the analysis of near-field radiative heat transfer in one-dimensional multi-layered structures. The method is based on the solution of dyadic Green's functions, where the amplitude of the fields in each layer is calculated via a scattering matrix approach. Several tests are presented where cubic boron nitride is used in the simulations. It is shown that a film emitter thicker than 1 μm provides the same spectral distribution of near-field radiative flux as obtained from a bulk emitter. Further simulations have pointed out that the presence of a body in close proximity to an emitter can alter the near-field spectrum emitted. This algorithm can be employed to study thermal one-dimensional layered media and photonic crystals in the near-field in order to design radiators optimizing the performances of nanoscale-gap thermophotovoltaic power generators.     

Numerical analysis of the reflection and absorption of electromagnetic wave in nonuniform magnetized plasma slab

In this paper, a model for calculating the reflection and absorption powers of electromagnetic wave (EM wave) in nonuniform magnetized plasma slab is given out based on layer propagation theory. The effects of various plasma parameters and different values of magnetic field intensity on the reflected and absorbed powers are discussed. The results illustrate that the thickness of plasma seldom affects the reflection of radar wave, but it can broaden or reduce the absorption width. Meanwhile, the background magnetic field intensity has an influence upon the results, and it could change the resonance spectrum of magnetized plasma. We also find out that, with appropriate plasma density, collision frequency and magnetic field intensity, more than 90% of radar wave power can be absorbed and the resonant absorption band is about 2 GHz.     

Quantum-dot superluminescent diode: A proposal for an ultra-wide output spectrum

We propose a novel superluminescent diode (SLD) with a quantum dot (QD) active layer, which should give a wider output spectrum than a conventional quantum well SLD. The device makes use of inhomogeneous broadness of gain spectrum resulting from size inhomogeneity of self-assembled quantum dots grown by Stranski– Krastanow mode. Taking a design made out in the In_xGa_1-xAs/GaAs system for example, the spectrum characteristics of the device are simulated realistically, 100–200 nm full width of half maximum of output spectrum can be obtained. The dependence of the output spectrum on In composition, size distribution and injection current of the dots active region is also elaborated.     

Calibration of hydrophones in a field with continuous radiation in a reverberating pool

We examine a method for estimating the transient impedance of an emitter and a receiver in a free field based on sliding complex averaging of the frequency dependence of the transient impedance of the emitter and the receiver obtained under continuous emission in an undamped pool. The method makes it possible to weaken the influence of reflected signals and to obtain frequency characteristics almost coinciding with measured ones in free-field conditions. We present results from experimental studies of the method and its application for calibration of hydrophones by field with the reciprocity method in a reverberating field.     

Applications of light emitting diodes as sensors of their own emitted light

In literature, it is known that a Light Emitting Diode (LED) could be used as a light sensor. It is also known that its emitted light spectrum and sensitivity spectrum can be partially overlapped. This work presents how commercial LEDs can be used as light emitters and simultaneously as sensors of the reflected portion of the light emitted by themselves. The realized devices present a unique characteristic: the transmitter and the receiver coincide spatially as they are the same device. This ensures the perfect overlapping between transmission and reception radiation lobes that could provide many benefits in several applications like as distance measurements or image sensors. Some simple electronic configurations that use LEDs as detectors of their own emitted light are presented. It has been also demonstrated how these LEDs_Tx-Rx can work as image sensors by acquiring an image of a simple test object, and how they can realize distance sensors with respect to other known techniques. Further advantages can be obtained by realizing LED_Tx-Rx array in single integrated devices. With the realization of such devices, it will be also possible to experiment new constructive solutions for commonly used applications, without the need of using separate emitter and receiver.     

Simulation of electroluminescence of quantum dot-based microcavity light-emitting device

We present a detailed analysis and computations of the emitted radiation spectrum for quantum dots (QDs) microcavity light-emitting device, where the total physical thickness of the cavity spacer was kept at 254 nm which corresponds to the wavelength of the mode number (m) = 1 resonant mode of the cavity. Our calculation gives good results for QD diameter only from 1.2 to 6.4 nm. The computations are used to examine how the emitted radiation spectrum can be optimized by varying the position of the light-emitting layer, the type of cathode material, the choice of hole transport layer material, and the thickness of electron transport layer, QD layer, and hole transport layer. These studies showed that the variation of layers geometry and the position of the light-emitting layer will optimize the output intensity and the radiation spectrum and varying the ETL and QD layer thickness will have a more effect on the emitted spectrum than varying HTL thickness. In addition, we have examined the effect of using different quantum dots sizes in emission layer. On the other hand, we have investigated the difference between the electroluminescence (EL) emissions for microcavity device in comparison with the non-cavity device, and we have found that the full width at half maximum (FWHM) of the EL is reduced from 45 nm for the QD non-cavity LED to 30 nm for the output of a resonant microcavity device. Finally, we have investigated the compatibility between our calculation and the experimental results and found a fairly good agreement between them.     

Wavelength tunable ultra-short pulses based on a flat broadband spectrum generated in a nonlinear ytterbium-doped fiber amplifier

We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power.Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum(center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges.Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm,the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around1200 nm, and its output power and pulse width are 40 m W and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.     

Amplifying discharge instabilities in the emission channel of a plasma electron emitter

We consider the amplification of oscillations of the plasma parameters in the emission channel of an electron source with a plasma emitter. The relationship between the modulation level of the emission current and the oscillations of the concentration and potential of the emitting plasma is determined. The amplification of the discharge instabilities is seen to be a function of the ratio of the size of the boundary layer in the channel to the channel radius. The amplification factor is calculated as a function of the emission current and the accelerating voltage. The change in the plasma parameters at the emission boundary for a plasma shift in the channel is taken into account.Tomsk Academy of Control Systems and Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–76, Feburary, 1994.     

The frequency width of symmetric modes of an aluminum plate: manifestation of a complex slowness on a frequency spectrum

The evolution of the experimental frequency width of symmetric modes of an aluminum plate is studied as a function of the angle of incidence below the first critical angle. It is found that the frequency width predicted by resonant scattering theory, corrected for the directivity of emitter and receiver, generally explains the experimental frequency width well. However, large discrepancies remain for the frequency width of the S1 mode at angles of incidence larger than 9 degrees. It is demonstrated that these are caused by not taking into account the complex nature of the slowness of the plate mode. This suggests that there is a need for a theory that models the interaction of a beam of ultrasound, bounded in space and time, with an elastic plate.     

Two-photon scattering by a cavity-coupled two-level emitter in a one-dimensional waveguide

We show that two-photon transport can be modulated by a two-level emitter coupled to a cavity in a one-dimensional waveguide. In the ordinary case, the transmitted light has a wider frequency spectrum than the situation without the cavity because it is reflected and scattered many times. But when the two photons are resonant with the cavity resonance reflection frequency, the frequency spectrum of the transmitted light becomes narrower than that without the cavity. This means that properly tuning the cavity resonance frequency can improve the photon–photon interaction. In addition, we show that the two-photon intensity correlation functions are nearly opposite to each other at the two sides of the emitter transition frequency rather than the same, which is exactly the Fano resonance line shape for two photons. Such an effect is important for lowering the power threshold in optical bistable devices and for sensing applications. When the emitter transition frequency equals to the cavity resonance frequency for a high-Q cavity, our results agree with the recent experiments and theories.     

Zero permittivity band characteristics in one-dimensional plasma dielectric photonic crystal

We consider the oblique propagation of electromagnetic waves in one-dimensional plasma dielectric photonic crystals, the superlattice structure consisting of alternating plasma and dielectric materials using transfer matrix method. Our results show that photonic band gaps for all polarizations can be obtained in one-dimensional plasma dielectric photonic crystals. These structures can exhibit a new type of band or gap, for the incidence angles other than normal incidence, near frequencies where the electric permittivity of the plasma layer changes sign. This new band or gap arises, from the dispersive properties of the plasma layer, only for TM polarized waves and its width increases with the increasing angle of incidence. This differential behaviour under polarization can be utilized in the design of an efficient polarization splitter. The band characteristic is affected by the plasma width, the plasma density, dielectric width, the dielectric constant of the dielectric medium and angle of incidence.