Phase of radiation from stimulated emission

With the help of the quantum theory of radiation, it is shown that the stimulated radiation from an atom has the same direction and phase dependence as the incident stimulating radiation.     

电子束泵浦XeCl准分子激光器输出特性

为了确保窄脉宽XeCl准分子激光系统获得高峰值功率紫外激光脉冲,实验研究了紧凑型四向电子束泵浦XeCl准分子激光器的输出特性。通过调节激光腔室气体介质的总气压和气体摩尔比、激光器的充电电压、二极管阳极钛箔厚度等参数,发现了激光能量随以上条件的变化规律,分析得到了激光器运行的最佳条件。在最佳条件下XeCl准分子激光器的脉冲能量大于100 J、脉宽约200 ns,电光效率约为5.81。另外,通过改变激光器内部Marx发生器的开关气压,研究了紧凑型电子束泵浦XeCl准分子激光器输出激光脉冲的延迟抖动特性,发现激光脉冲的延迟抖动可优于20 ns。研究结果表明:紧凑型电子束泵浦XeCl准分子激光器可实现脉冲抖动小于20 ns、103 J的高能紫外激光输出,可满足窄脉宽XeCl准分子激光系统运行的需要。     

Photon-enhanced field emission from CdS single crystals

In a previous experiment, field emission was observed from sharply pointed CdS single crystals. The experiments have now been extended, illuminating the tip with light from a pulsed argon-ion laser. It was found that (a) the voltage threshold at which emission can be observed is reduced, typically from 500 to 400 V, (b) under some conditions, the emission is increased by a factor of 103, (c) this emission persists for more than 2×10?2s after the laser pulse and appears to have two characteristic decay times, (d) the emission is approximately proportional to the light intensity and (e) the greatest photo-enhanced field emission was obtained with the laser light shining axially on the emitting area of the tip.     

ZnO纳米多晶颗粒激射模式的特性研究

利用飞秒脉冲激光激发,研究了均匀沉淀法制备获得的ZnO纳米多晶颗粒的室温紫外受激发射.在高密度激发功率下,其发射光谱表现为宽的发射背景上一系列的锐窄结构,且两相邻尖锐峰间距基本相同,即激射模式具有等间距性质.改变激光激发强度,发射谱带红移,但激射模式间距不随激发强度变化而变化;进一步比较三组典型粒径的ZnO纳米多晶颗粒样品发射光谱的激射模式,发现模式间距也相同,即激射模式间距与粒径也没有关系,不同于传统的谐振腔理论.     

Modulation of the characteristics of intense picosecond stimulated emission from GaAs

Intense picosecond stimulated emission from the face of a thin GaAs film is studied. The emission is observed when GaAs is pumped with high-power picosecond optical pulses. It is found that the dependences of the emission energy on the photon energy, the picosecond delay between two pump pulses, and the distance between the active region and the face are modulated. Modulation is taken to mean the appearance of protrusions or peaks in any of the mentioned dependences. The modulation parameters for the dependences under consideration are found to be related by expressions that make it possible to suggest the following. The modulation of characteristics is caused by a common (not yet conclusively identified) mechanism of self-modulation of the emission spectrum. This mechanism is related to an ultrafast nonlinear interaction between a highly photoexcited semiconductor and the pump radiation and stimulated emission. There is indirect evidence that this mechanism also gives rise to an amplitude modulation of the emission in a picosecond time interval.     

Improved short-pulse pumping of stimulated Raman scattering in leadvapor

Improved efficiency for short pulse stimulated Raman scattering (SRS) in Pb vapor is obtained using accumulation of gain between a closely spaced pulse pair. The peak power conversion efficiency of the delayed pulse is increased to 40%, in contrast to 15% for a single pulse. Numerical modeling gives good agreement with observation, and suggests that this enhancement is caused by the continued presence of coherent excitation produced by the first pulse. The dependence of the enhancement in delayed-pulse efficiency on Xe buffer gas pressure in the Pb-vapor cell is attributed to changes in the transient response time T₂ of the Pb medium with Xe pressure     

Changes in the spectra of picosecond stimulated emission from GaAs accompanied by signs of electron-phonon interaction

A nonmonotonic variation in the width of the emission spectra ?????_s of GaAs as the energy of the pump photon ???_ex is varied is observed at a fixed energy of a picosecond pump pulse W _ex giving rise to intrinsic stimulated emission. In the case of this nonmonotonic variation, the largest width of the spectra has been found to be close to the parameter ??, which is determined by the energy of a longitudinal optical (LO) phonon and by the masses of an electron and a heavy hole. As the nonmonotonicity of the dependence ?????_s = f(???_ex) becomes more pronounced, modulation of this dependence and the dependence of the spectrum amplitude on ???_ex are observed. The modulation features signs of relation to the electron-LO-phonon interaction. The observed evolution of the modulation is not inconsistent with published suggestions concerning the development and destruction of screening of the electron-LO-phonon interaction in the case of a dense electron-hole plasma. The level of radiation losses in the sample affects the modulation and nonmonotonicity.     

Spontaneous and stimulated emission from magnetron-deposited ZnO-SiO2-Si thin-film nanocavities

The spontaneous and stimulated emission spectra from optically pumped zinc oxide nanolayers on oxidized silicon were studied. Single-mode lasing with a wavelength of 397 nm was observed for a coupled longitudinal mode of the ZnO film at room temperature. For the thin-film nanocavities of ZnO-SiO₂-Si, optimal parameters that allow the lowering of the threshold and the attainment of single-mode lasing are determined.     

Optically pumped stimulated emission in ZnSe

Stimulated emission in optically pumped ZnSe is reported. The emission at 4580 Å is observed at temperatures up to 250 K in solution grown ZnSe crystals with improved near band edge luminescence.     

Wavelength tuning of the stimulated emission from GaAs and CdSe electron-beam-pumped lasers

The wavelength at which the stimulated output from a number of electron-beam-pumped semiconductor lasers peaks is a function of the time after the start of the pumping pulse. In general, the output intensity reaches a maximum at short wavelengths considerably before it peaks at the longest. Detailed observations of the wavelength shifts of the peak output as a function of both time and pumping current are reported here for both CdSe and GaAs laser crystals. It is found that the rate of shifting of the wavelength peak (tuning rate) as a function of electron-beam pumping current is very similar in both functional form and magnitude in the two materials. Furthermore, the behavior of the tuning rate is dependent on whether or not lasing action occurs in the crystal under examination. For a crystal in which lasing action is obtained, the tuning rate saturates for pumping current densities above threshold. In contrast, for a nonlasing crystal, the tuning rate is a linearly increasing function of the pumping current density. The implications of these results are discussed with reference to previously reported work concerning shifts with respect to the band edge of the stimulated emission from semiconductor lasers.     

Spectroscopic and stimulated emission Characteristics of Nd/sup 3+/ in transparent YAG ceramics

Nd: YAG ceramic materials have been synthesized using vacuum sintering technique with the raw materials prepared by the nano-crystalline methods. The spectroscopic studies suggest overall improvement in absorption and emission and reduction in scattering loss. Judd-Ofelt analysis has been employed to compute the relevant spectroscopic and radiative parameters of the material. The SEM and TEM measurements reveal the excellent optical quality of the ceramic with low pore volume and narrow grain boundary. Fluorescence and Raman measurements reveal that the Nd/sup 3+/-doped YAG ceramic is almost equivalent to its single-crystal counterpart in its radiative and nonradiative properties. Individual Stark levels for /sup 2s+1/L/sub J/ manifolds are obtained from the absorption and fluorescence spectra and are analyzed to identify the stimulated emission channels possible in the Nd: YAG ceramic. Laser performance studies favor the use of high-concentration Nd: YAG ceramics in the design of an efficient microchip laser. With 4 at% Nd: YAG ceramic acting as a microchip laser, we obtained a slope efficiency of 40%. High-power laser experiments yield an optical-to-optical conversion efficiency of 30% for Nd (0.6 at%):YAG ceramic as compared to 34% for an Nd (0.6 at%):YAG single crystal. The oscillation experiments at 1.3 mm gives a slope efficiency of 35%. Optical gain measurements conducted in these materials also show values comparable to single crystal, supporting that these materials could be suitable substitutes to single crystals in solid-state laser applications.     

Role of spontaneous emission in the dynamics of mode locking by synchronous pumping

Numerical simulations tracing the pulse evolution in the case of mode locking by synchronous pumping are presented. It is argued that strictly steady-state pulses are impossible in principle because the wings of the pulses are embedded in background radiation generated by spontaneous emission. The simulations demonstrate that the perturbations introduced by the stochastic background can be severe, and that these can apparently be minimized only at the expense of the overall quality of the mode-locked pulse envelopes.     

钾分子的二步泵浦光离解受激辐射

运用从H_2喇曼管出射的红外相干辐射,第一步将K_2分子激发到A~1∑_u~+态;第二步再由染料激光将其激发到高位g态的离解限,从而产生光离解受激辐射.     

Spontaneous and stimulated emission from CdxHg1−x Te semiconductor films

The experimental data on observation of spontaneous and stimulated emission from thin epitaxial Cd_xHg_1?x Te films optically pumped by Nd: YAG laser radiation are reported. A simple theoretical model is suggested to describe the initiation of population inversion under these conditions. The parameters realized under the experimental conditions are theoretically estimated.     

Observation of stimulated emission, line narrowing, and red shiftof emission peak from optically-pumped rectangular cross-sectional GaNoptical waveguides fabricated by selective growth

The authors examined low-loss III-V nitride optical waveguides for fabrication on sapphire substrates for active devices using a selective-area growth technique. A rectangular cross-section waveguide can be created by adjusting crystal growth conditions. A stimulated emission peak at 362 nm, line narrowing, and a red shift were observed from the selectively grown GaN waveguides by optical pumping     

受激辐射损耗超分辨成像技术研究

受激辐射损耗显微成像(STED)是一种超分辨荧光显微成像技术,它能够突破传统光学衍射极限的限制,把远场光学分辨率提高到百纳米以内,被广泛应用于生物医学等领域,是目前光学显微成像领域研究的热点之一。采用了一种基于超连续谱皮秒脉冲白激光光源的STED显微系统,实现超分辨成像。并从精密合束、脉冲延迟和损耗光残留光强几个方面探讨系统优化,从而获得最佳的成像效果。对直径约25 nm荧光微球成像实验的数据表明:该系统成像分辨率可达约60 nm,分辨能力远远高于衍射极限。另外,系统成功实现了对核孔复合物、微管和微丝等一系列生物样品的超分辨成像,共聚焦成像中某些模糊不清的结构在STED成像中清晰可辨。     

Pulsed stimulated emission from N, C, Cl, and F atoms

Eighteen electrically pulsed parent compound-helium mixtures yielded N, C, Cl, or F atom lasing. The laser pulses appeared as one or more peaks at each wavelength. New lasing on the chlorine wavelength (3.5443 μmvac) was observed from a Cl2-He mixture.     

同步脉冲泵浦抑制光纤放大自发辐射实验研究

放大的自发辐射(ASE)是影响掺Yb3+光纤放大器效率的重要因素之一。为了抑制ASE,本文从放大器的泵浦方式着手,设计并搭建了同步脉冲泵浦的掺Yb3+双包层光纤放大器,证实了其具有明显抑制ASE的效果。在重复率400 Hz时,将平均功率15 mW,脉宽500 ns的信号光放大至170 mW,实现增益10.5 dB。同时实验研究了不同泵浦脉宽对于ASE生成的影响。