OMA-2快速测定微秒级脉冲灯的光谱分布和光谱效率

采用OMA-2系统,测定了脉宽为3微秒的脉冲氙灯在2200～8800(?)波段的光谱分布和光谱效率。 研究了不同放电电压、不同充气压力对脉冲灯光谱输出的影响。结果表明,随放电电压和充氙压力的增加,脉冲氙灯的紫外光谱效率从13％增加到17％左右,紫外总辐射能量也显著提高。     

“LO-Phonon” correlation between picosecond superluminescence spectrum and special features of absorption spectrum in GaAs for non-Fermi distribution of carriers induced by picosecond light pulse

Dense electron-hole plasma (EHP) was generated in a GaAs layer by a picosecond light pulse. Superluminescence phenomenon and local deviations of the light-absorption spectrum from that calculated for the Fermi distribution of EHP were observed. Deviations in the enhancement region, where the measured gain is less than the calculated one, and in the absorption region, where the opposite relation takes place, were named the “hole” and the “protrusion”, respectively. The shape of the hole was similar to the shape of the superluminescence spectrum in the spectral region of the hole, as well as to the shape of the protrusion in the absorption spectrum. Both the spectral width of the spike, which was roughly equal to that of the hole, and its spectral position with respect to the superluminescence spectrum were governed by the energy of the longitudinal optical phonon. These correlations were attributed to superluminescence-induced depletion of levels at the conduction-band bottom and their filling with electrons due to the emission of longitudinal optical phonons.     

Near-UV spectral efficiency of high-current xenon flashlamps

A discussion is given of the limiting spectral efficiency of flashlamps that are used to pump lasers. Absolute measurements indicate that 4.5 percent of the capacitor-bank energy appears as radiant energy in the region 2500-2900 Å (the nominal pump band of the iodine photodissociation laser) for the flashlamps studied in this work. A large portion of the radiation in this band is due to bound-bound processes and not solely recombination radiation and bremsstrahlung as is usually assumed.     

Energy characteristics of excitons in structures based on InGaN alloys

Samples containing ultrathin InGaN layers that emit radiation in the spectral range from the ultraviolet to yellow region are studied. The samples are grown by metal-organic vapor-phase epitaxy. The Urbach energy, the localization energy of excitons, and the activation energy of charge carriers are determined to characterize radiative and nonradiative processes in the quantum dots and barriers of the structures. It is shown that these energy parameters are linearly dependent on the photon energy in the range from 3.05 to 2.12 eV. It is established that temperature variations in the emission intensity are due to the increase in the number of charge carriers thermally activated from the quantum wells into barriers as well as due to the enhancement of scattering of free excitons at defects.     

Detailed study of above bandgap optical absorption in HgCdTe

HgCdTe remains the material of choice for high-performance infrared (IR) detectors due to its tunable direct bandgap energy corresponding to the IR spectral region, and the advancement of HgCdTe materials growth and processing technologies. Accurate knowledge of the HgCdTe optical absorption coefficient is important for IR detector design, layer screening, and device analysis. The spectral response for IR detectors is dependent on optical absorption above the bandgap energy, where much of the study of absorption coefficient in HgCdTe has focused on the bandtail region. In this work, the optical absorption coefficient was studied by theoretical bandstructure calculations and experimental measurements on HgCdTe layers using techniques of IR spectroscopic ellipsometry and IR transmission. The theoretical and experimental results suggest that the absorption coefficient between 600 cm⁻¹ and 5,000 cm⁻¹ is related to energy relative to bandgap with a fractional exponent between 0.6 and 1, rather than the previously used expressions relating to a parabolic or hyperbolic bandstructure. The fitting parameters for Hg_1-xCd_xTe with x=0.22–0.60 are presented to develop a model for the optical absorption coefficient spectra. The calculated detector spectral response using the new and previously reported absorption coefficient models suggests that next generation IR detectors employing multilayer structures with graded compositional profiles will likely benefit from this new model.     

多光谱可见光图像与高分辨率图像的分维融合

针对遥感图像,提出了一种遥感多光谱可见光图像与遥感高分辨率全色图像融合的小波分维算法.利用小波变换的方向选择}生,对遥感多光谱的1分量和遥感全色图像进行小波分解,进而在不同子带中进行遥感图像融合,低频部分采用基于区域能量的融合算法;高频部分使用21×21的窗口加窗逐点计算分维作为权系数进行融合;最后将得到的灰度融合图像...     

Spectral narrowing of a flashlamp-pumped high-energy dye laser by two-stage injection locking

This paper proposes a new scheme of multistage injection locking controlled by a narrow-band CW dye laser to obtain spectral narrowing of a high-energy flashlamp-pumped dye laser (FLPL). The spectrum of FLPL with an output energy of 23 J was successfully narrowed to 0.7 GHz by this method. A narrow-band CW radiation was injected into the cavity of a small FLPL, then its locked output emission was injected into the cavity of the high-energy FLPL. With a CW injected power of 15 mW, about 70 percent of the output energy of the final laser was concentrated into the same spectral region as the injected CW radiation. The effective power gain obtained was as large as4 times 10^{8}. Using coupled rate equations based on a simplified model, the injection-locking phenomena were analyzed. This model makes it possible to derive the locking efficiency as a function of the injected power in an explicit form, and gives an insight for experiments. Some performances of injection-locked operation were studied experimentally.     

Analysis of the uniform magnetic field free-electron laser with scalarized photons in the microwave-spectral region

The recently developed concept of scalarized photons (formally photons of any polarization) is used to analyze the spontaneous and stimulated emission in the uniform magnetic field free-electron laser in the microwave spectral region. In fact, this free-electron laser is the simplest of many other, wiggler and wiggler-free free-electron lasers whose analyses could be done with scalarized photons in the small signal regime and whose physical parameters can be conveniently chosen for radiation to be generated in the microwave spectral region. As to the uniform magnetic field free-electron laser, which is treated here in some detail, with the electron beam energy of up to 10 MeV and the uniform magnetic field of up to 4 Tesla, the radiation (occurring with the fundamental and higher harmonic frequencies) can cover easily a 10 to 10,000 GHz spectral region.     

Optical properties of doped bismuth telluride crystals in the region of plasma effects

The optical properties of bismuth telluride crystals doped with donor-and acceptor-type impurities are studied. The fact that energy corresponding to the resonance frequency of plasma oscillations of free charge carriers (plasmons) approaches the band-gap energy is detected in the infrared spectral region, where the main elementary excitations in the electronic system of these materials are observed. The mentioned approach of energies varies the intensity of electron-plasmon interaction, which affects the recombination processes in the materials widely used for the fabrication of thermoelectric energy converters.     

A study of photon emission from n-channel MOSFET's

It is known that an n-channel MOSFET, operating in the saturation region, is accompanied by visible light emission. The spectral distribution of this emitted light is reported in this paper for the first time. It behaves as exp (-α . hv) under various bias conditions (α: constant); the energy state of hot electrons is described as a Maxwell-Boltzmann distribution. The hot-electron temperature in an n-channel MOSFET is experimentally evaluated from the photon spectrum analysis. As compared with the electric field strength calculated by two-dimensional simulation, the hot-electron temperature is found to be determined as a function of the electric field strength in the drain avalanche region.     

Free electron laser spectral dynamics with a modulation of electron beam energy

Recent experimental and theoretical works on free electron laser spectral dynamics have pointed out the difficulty to obtain a narrow and stable spectrum operation. This goal can only be achieved by avoiding the sideband generation leading to a broadband and unstable spectrum. Tapered wiggler and two-frequency wiggler are well suited for combining sharp spectrum and high efficiency but are not really compatible with a wide tunability of laser light. Filtering sidebands is a good way for lower power experiments but it seems to be difficult to conceive wideband filters, specially in the far-infrared region. Modulation of electron energy is a new potential soft way for controlling the spectral dynamics of longpulse free electron laser. Spectral dynamics under the modulation is investigated in the linear and non-linear regimes in the far-infrared region. Simulations show that a pulsed and sharp spectrum behavior can be obtained by optimizing the modulation parameters. The interest of such a method for the far-infrared experiments is discussed.     

Comparison of the output spectra of krypton and xenon filled flashtubes

The spectral output of krypton filled flashtubes has been investigated and compared to that of xenon filled tubes. It was observed that although xenon has a higher luminous efficiency than krypton, the krypton output is 150 to 200 percent of the xenon output at 810 nanometers depending on the input energy level. The implication is that krypton is a more efficient pumping source for lasers with an absorption band in the region of 810 nanometers.     

Excitation photocapacitance study of EL2 in n-GaAs and its relation to non-stoichiometry

The excitation photocapacitance measurements are performed on n-GaAs to obtain charge transition characteristics of EL2 defects in a full spectral region. It is shown that the threshold photon energy for EL2⁺⁺ to EL2⁺ transition is changed as a function of the primary excitation photon energy. It is also shown that the Frank–Condon shifts (d_FC) changed. It is considered that the lattice relaxation around the EL2 defect is affected by the deviation from the stoichiometric composition.     

Minimized Dual-band MIMO Antenna with High Isolation for 5G and WLAN Applications

One of the important means by which 5G can be implemented is by Ultra-Dense Multi-Tier future cellular network. We have studied the effect of the densification of network, Signal to Noise plus Interference ratio (SINR), network load, channel and channel bandwidth on the spectral efficiency and energy efficiency of this system. The importance of the spectral efficiency is also discussed. It is observed that as network load increases, spectral efficiency and energy efficiency decreases for given network bandwidth. which can be improved with the help of SINR or the densification of network. We have found out the exact higher modulation method M-Quadrature Amplitude Modulation (M-QAM) used for the given system and how it can be improved. By using higher M-QAM method, we can transmit more bits simultaneously. The spectral efficiency and energy efficiency of the system increases. It was found that as network bandwidth increases, spectral efficiency got decreases. We have also found the optimum value of bandwidth to maximize the spectral efficiency of this system.

     

二维划分反馈控制的星模拟器光源光谱匹配精度提升方法

为提高星模拟器光源系统光谱匹配精度,首先设计并搭建了基于数字微镜的星模拟器光源系统;其次,根据按波长标定的区域光谱进行遗传算法的光谱拟合,结果表明该方案拟合光谱与目标光谱存在一定匹配误差;最后,为提高光谱匹配的精度,提出了按波长和能量二维划分区域的误差反馈及精度提升方法。实验模拟了色温为2 550、4 766、6 576、8 910 K光源,结果表明相较于波长方向一维划分的反馈方法,光谱匹配最大误差分别下降了55.7%、50.6%、45.2%、42.2%,极大地提升了星模拟器光源系统的光谱匹配精度。该研究旨在补偿该类色温匹配误差所引入的星敏感器角检测误差,达到高精度星敏感器的定标精度要求。     

Power spectral density bounds (Corresp.)

The determination of a power density spectrum from a finite set of correlation samples is an ill-posed problem. Furthermore. it is not possible even to bound the values that consistent power density spectra can take on at a particular point. A more reasonable problem is to try to determine the total spectral power in some frequency interval. Although this power cannot be determined exactly, upper and lower bounds on its possible values can be determined. This observation leads to a unified treatment of certain classical and modern spectral estimation techniques and to new interpretations for two data adaptive spectral estimators. maximum likelihood method (MLM) and data adaptive spectral estimator (DASE). According to these new interpretations. MLM and DASE provide upper bounds on spectral power in a specified frequency region subject to the assumption that the spectral density is constant in that region. These methods make no use of an extendibility constraint that can be used to obtain tight upper bounds, as well as nontrivial lower bounds on power. Cybenko has studied a related problem of bounding windowed power, for an arbitrary window, with no assumptions about the form of the spectral density. A new type of classical resolution limit for these bounds is derived and a numerical example is presented.     

Energy efficiency and spectral efficiency tradeoff in downlink OFDMA systems with imperfect CSI

In this paper, we investigate the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in downlink orthogonal frequency division multiplexing access (OFDMA) systems, whilst considering the channel estimation cost and the corresponding effect of imperfect channel state information (CSI) on SE and EE. The problem is formulated as a multi-objective optimization to determine the optimal pilot transmission power, data transmission power and subcarrier assignment, and then transformed into a single-objective optimization problem, which is a non-convex mixed-integer nonlinear programming (NCMINP) and NP-hard. To address it, we propose an efficient algorithm by adopting alternating optimization and convex optimization methods in lower power region as well as approximate conversion and branch-and-bound methods in high power region. Simulation results analyze and validate the performance of EE-SE tradeoff.     

背面Ar~+轰击对n-MOSFET低频噪声的影响

研究了低能量背面Ar+轰击对n沟MOSFET低频噪声的影响 .用低能量 ( 5 5 0eV)的氩离子束轰击n沟MOSFET芯片的背面 ,能改善其饱和区和线性区的低频噪声频谱密度 .饱和区低频噪声的减小可用载流子迁移率模型解释 ,而线性区低频噪声的减小可用载流子数模型解释 ;其变化的原因可能与氩离子束背面轰击后反型层电子的有效迁移率、二氧化硅中的固定电荷密度以及硅 二氧化硅界面的界面态密度的变化有关.     

High-power operation and scaling behavior of CW optically pumped FIR waveguide lasers

High-power far infrared (FIR) laser operation at the 10- 100 mW level is described for wavelengths throughout the 40 μm-1.22 mm spectral region. These data correspond to order of magnitude improvements in converting CO2laser energy into FIR laser output. This improved FIR laser performance is attributed to a waveguide laser geometry with reduced losses for the CO2pump and also to a new method of output coupling. The basic design concept of the efficient laser resonator is discussed as well as the prospect for further increases in laser performance through improved efficiency and sealing.     

Characterization of an ultrahigh peak powerXeF(C→A) excimer laser system

The gain characteristics of an electron-beam pumped XeF(C→A) excimer amplifier operating in the blue-green spectral region were investigated for several laser pulse lengths. Saturation energy densities of 50 and 80 mJ/cm² were measured for injected laser pulse durations of 250 fs and ~100 ps, respectively. A gain bandwidth of 60 nm was observed with ~100-ps pulse injection. Using an optimized unstable resonator design, the laser amplifier has produced 275-mJ pulses with a pulse duration of 250 fs and a 2.5 times diffraction-limited beam quality, making the XeF(C→A) amplifier the first compact laser system in the visible spectral region to reach peak powers at the terawatt level