激光等离子体相互作用中的二次谐波发射

为了判别激光等离子体相互作用中发射二次谐波(2ω)的不同机制,特别是研究呈现较复杂结构的2ω谱成分的发射规律,我们已在相当宽的激光强度范围(10~(12)～10~(15)瓦/厘米~2)、不同的激光偏振与各种激光入射角(0°,20°,45°等)情形下,系统地观察了2ω的空间分辨的后向、90°方向散射的谱及其二维分辨的空间发射特性。实验是利用1.06微米、100微微秒脉宽与带宽<1(?)的高强度单束激光照射各种材料(Be、CH_2、Al、Si、Ag、Mo、Ta和Au)平板靶、多层薄膜靶以及几种微球(玻壳、CD_2实心球)靶完成的。激光等离子体相互作用的特性另外还用多种X光、离子、后向反射激光特性以及预脉冲激光方面的诊断进行监测。     

单向二次谐波输出

一、基本装置和原理图1所示装置是洛克希德导弹和空间公司研制成的用于由Nd:YAG激光器的内腔倍频获得单频单向二次谐波输出。就图中几何形状和边界条件而言,对1.6和0.53微米辐射的无限平面波的非线性互作用研究结果表明,单向二次谐波总功率取决于下式:P_2 (l_c)∝4B~2l_c~2sinc~2(ΔKl_c/2)×cos~2(ΔKl_c/2+φ_2/2-φ_1)(1)式中sin CX=sin X/X,B=μ_0ω_2~2E_1~2/     

高效产生二次谐波

美国亚利桑那大学光学科学中心的G. I. Stegeman和C. Liao对用MNA薄膜——一种已知的效率最高的非线性光学材料——在可见光区高效率地产生二次谐波的条件作了数值模型的描述。在提出的方案中，MNA的高折射率色散用厚度色散补偿(在考虑的最佳情况下)，预期总的倍频效率为8.6%,1.06微米光束的起动功率为100毫瓦。这种技术对用半导体激光、静电印刷和卫星对水下通讯的大电子显示器（发光二极管)，红外光源产生可见光束可能是重要的。     

激光等离子体在垂直入射方向上发射的二次谐波的空间结构

在激光与等离子体的相互作用中,激光功率超过某些值时会出现很多反常现象。如共振吸收、受激布里渊散射、受激喇曼散射和各种衰变不稳等;从而会导致如众所周知的那样,单一频率的电磁波入射到非线性介质时由于二次极化效应而引起倍频光辐射——在临界面附近,通过共振吸收,入射光的能量转变为二次谐波能量,或者在临界面外,通过参量衰变也可导致二次谐波的发射。     

二次发射体简介

一、二次发射体的分类二次发射体可分为:纯金属或合金、合金薄膜、金属陶瓷、金属陶瓷厚膜、半导体等类型。二次发射是一种复杂的现象,目前仍处于探索中。这里简单介绍一下常用材料的二次发射特性及有效二次发射体的基本数据。     

腔内二次谐波发生器

日本东京芝浦电气公司发表了一种腔内二次谐波发生器。在光谐振腔内置放一个二次谐波发生器件,对由激光振荡器发射出的射束的倍频有影响。在这种情况下,要求作为二次谐波发生器件用的非线性光学晶体应符合以下条件: 1.此晶体要能够从基波到谐波之间进行极为有效的变换。 2.此晶体的光损耗一定要小,尤其要具有良好的光均匀性,即基波和谐波之间的相     

空调器中的二次电流谐波

空调器(定速机)产生二次谐波是个令人困惑的问题,文章运用电磁理论基础,简述了异步电动机不对称运转在定子绕组上产生二次谐波电流发射的原因,发现了异步电动机理论的不足,解释了空调器(定速机)二次电流谐波超标的根源,并对理解和应用GB17625.1-2003有关空调器(定速机)测量条件要求提出了参考意见.     

冷积银膜的二次谐波研究

冷积金属膜在退火过程中对外场的二次谐波响应,理论预计可同时观察到局域的和非局域的表面等离子体激光(SPP)对二次谐波的增强.在超高真空环境下和120～400K退火范围内观察到了冷积银膜表面这两种SPP激发,讨论了它们与入射场的角度关联特性.     

人体的光学二次谐波效应

在人体指纹谱的研究中我们发现人体的光学二次谐波现象。通过测试进一步观察了人体光学二次谐波效应的规律性变化，并从理论上对其机理进行了探讨。     

二次谐波细胞成像的研究进展

由于二次谐波(Second harmonic generation, SHG)技术具有探测深度深,对生物体的损伤小,时间空间分辨率高以及对结构的对称性敏感等特性,SHG成像成为近年来生物成像领域的研究热点.介绍了SHG成像技术的原理及其在细胞成像中的应用,重点介绍了基于染料标记的成像技术,特别是利用电压敏感染料,手性材料和金属纳米粒子作为标记的几种SHG细胞成像技术,最后展望了该技术在生物成像领域的应用前景.     

Quadratic solitons with gain and loss

Propagation of soliton signals in quadratic nonlinear media under conditions for second-harmonic generation in the presence of multiple-frequency-band absorption and amplification is addressed. The reshaping and energy redistribution of the multiple-frequency solitons under the action of the single-band loss and gain is investigated and shown in detail. New chirped localized solitary-wave solutions that exactly compensate loss and gain are presented. Practical implementation conditions are discussed     

Two- and four-wave mixing with saturable absorption and gain

An exact solution to a model of two- and four-wave mixing in photorefractive media with saturable gain and absorption is presented. Pump depletion effects are accounted for, and the procedure for matching two-point boundary conditions is given. Possibilities of multistable solutions are investigated, and procedures on how to deal with such situations are outlined. It is found that the energy transfer between waves is less effective in the nonsaturated regime as compared to the saturated regime. It is also established that the nonsaturated system is more stable than the saturated under the same conditions     

Bidirectional amplification with nonsaturable absorption and amplified spontaneous emission

A theory of bidirectional amplification is developed and applied to single-pass and double-pass laser amplifier configurations. The effects of nonsaturable absorption, longitudinal amplified spontaneous emission (ASE) gain saturation, and ASE line narrowing are included in a self-consistent formulation. An estimate of aperture scaling limitations due to transverse ASE is included. Laser performance is discussed for some conditions typical of large aperture, multikilojoule, rare gas halide (RGH) fusion amplifiers. This formulation permits tradeoff studies to be performed rapidly by altering variables spanning an eight-parameter space.     

Soliton switching in twin-core fibers with gain and loss

Soliton propagation and switching in twin-core nonlinear fibers with gain and loss have been investigated based on a pair of coupled nonlinear Schrödinger equations. We have found the fiber with equal amount of gain in both cores has the minimum ascending energy Δ? of 1.5K, while the fiber with a certain amount of gain in one core and the same amount of loss in the other core has the minimum switching threshold? _th of 2.05K. A new vector field is defined and its potential function is derived, which explains the switching behavior of the minimum? _th switch satisfactorily.     

Quantum-statistical properties of pulse amplification in opticalfibers with gain saturation

We studied the quantum-statistical properties of pulse amplification in erbium-doped fiber amplifiers (OFAs), including saturation of the atomic population inversion and pump depletion. We use a fully quantum theory to describe the atom-field interaction as wed as the light propagation. The generating function of the output photon number distribution (PND) is determined as a function of time during the course of the pulse, with an arbitrary input PND assumed. For input light with Poisson PND, the output PND is shown to be the Laguerre distribution with parameter 1 at all times smaller than the coherence time τ_c, even in the presence of nonlinear effects. An expression for the photon count moment generating function is found for counting times T≫τ_c. The mean pulse shape is shown to be altered by the nonlinear amplification. The variance is similarly altered, and the excess amplifier noise is greater at the leading side of the pulse     

Quality factors and effective-average modal gain or loss ininhomogeneous spherical resonators: application to two-photon absorption

A method is presented for calculating the quality factors (Q's) and the effective-average gain and loss coefficients for the modes of a dielectric sphere which has a spatial perturbation of the imaginary part of the refractive index. The method is applicable to gain calculations in spherical lasers, to spatial hole burning and to stimulated Raman scattering in spheres. A time-independent perturbation method is also used to compute the Q's of the resonances. Results computed using both methods are compared with analytical results for layered spheres. The methods are used to compute the near-resonance backscattering by a sphere having an intensity-dependent (two-photon absorption) loss     

Coupled-waveguide exchange-Bragg resonator filters: coupled-modeanalysis with loss and gain

Novel resonator filters made of two closely coupled asymmetric waveguides with phase-shifted exchange-Bragg grating, are investigated. Coupled-mode theory based on the normal modes is used to examine the effects of loss and gain on the filter spectral responses. The filter exhibits a total transmission at central wavelength and a rejection to the adjacent waveguide with high extinction ratio for other signals in the absence of loss and gain. Material loss reduces the transmitted power level and increases the filter bandwidth. With a certain amount of optical gain, good transmission can still be maintained in the presence of material loss. Proper control of the optical gain can lead to the amplification of both the transmitted and reflected powers at the central wavelength     

基于受激增益与自发衰减的激发－探测显微技术

基于激发-探测显微技术研究受激增益与自发衰减现象。采用脉冲二极管激光器（pu=635 nm作为激发光束）与锁模掺钛蓝宝石激光器（pr=780 nm作为探测光束）。受激增益部分,发射光束在频率f1被调制,利用光电二极管作为探测器（PDA 36A,Thorlabs）,探测光被相应地解调来提取透射方向的信号;自发损耗部分,探测光束在频率f2被调制,从探测荧光由光电倍增管以反射模式解调自发损耗信号。所有情形下使用高性能锁模放大器（HF2LI,Zurich Instruments）。锁模放大器的输出信号接着输入扫描单元的A/D通道用于图像重构。扫描速率设为频率500 Hz,与锁模放大器1.99 ms的时间常数相匹配。由解调荧光信号获取背景大大减少的荧光寿命和光学部分属于散粒噪声的图像。另外,此技术改善信噪比,提高类似多光子显微镜的穿透深度,无须昂贵的飞秒激光器。     

Ultrasonic loss and gain mechanisms in semiconductors

Several kinds of interactions of ultrasound in semiconductors are reviewed. The subjects discussed are the effects of interaction with 1) thermal phonons, which produce temperature dependent attenuation; 2) free carriers, which may give attenuation or amplification; 3) electrons bound to shallow donors, giving rise to attenuation at low temperatures; and 4) other ultrasonic waves, which may give attenuation or amplification. An introduction to relaxation effects is included.