A Novel Mirror for Cold Molecules with a Semi-Gaussian Beam

We propose a novel mirror for cold molecules with a blue-detuned semi-Gaussian beam and study the dynamic reflection process of cold molecules by Monte Carlo simulation. Our study shows that this mirror can realize a specular reflection of cold iodine molecular beam with a temperature of 30mK by a reflectivity of 58.2% when the semi-Gaussian laser power is 1.0 kW. When a semi-Gaussian CO2 laser beam with a power of 5.8 kW is used, the reflectivity of this mirror can reach about 100%.     

相位反射产生的激光场空洞现象及其与激光等离子体参数相关性研究

理论研究和数值模拟研究表明激光在等离子体中诱导的等离子体密度调制可以起类似布拉格反射镜的作用，使得后面的入射光在等离子体平均密度远低于临界密度的区域就对入射光产生相位反射.相位反射的发生会影响激光在等离子体中的传播，例如激光在等离子体中相对传播时会出现激光场空洞现象.进一步的理论和数值模拟研究表明，相位反射持续发生的时间以及反射率的高低与等离子体的密度、等离子体区域的长度、激光强度以及脉宽等因素密切相关，这些都会对激光在等离子体中的传输产生影响. 关键词： 相位反射 密度调制 激光等离子体 粒子模拟     

Prism reflectors for high power lasers

A new type of laser reflector is described in which the laser beam is split by frustrated total internal reflection and the components combined again. It has the properties of high reflectivity, high damage resistance, wide bandwidth and variable reflectivity. The design of two particular reflectors is discussed and their performance evaluated. One of these reflectors has the property of lateral inversion of the reflected beam, which is found to aid transverse mode selection in a ruby laser. As an application of the reflectors, a damage free, single transverse mode, mode-locked ruby laser is described.     

基于表面等离激元场的分子反射镜的理论研究

本文提出了一种基于微纳金属膜结构激发的表面等离激元场的分子反射镜新方案,利用中性分子与金属表面垂直方向上蓝失谐消逝波光场之间的偶极力相互作用,实现入射分子束的表面反射.理论计算了表面等离激元场的空间分布,用蒙特卡洛方法模拟了分子在该场中运动的动力学过程,得到了分子反射镜的反射率与相互作用时间和入射光强之间的关系.结果表明:当入射激光脉宽为10 ns,光强为I=1.0×109W/cm2时,纵向温度为10 mK,横向温度为1 mK的碘分子束反射效率达到55.89%,而且反射率随着入射光强的增大而增大.     

An Interferometric Method of Measuring Reflection Coefficients

A method for determining the reflection coefficients of optical elements, which is based on the use of a reflection interferometer, is proposed. The results of measurements with a He–Ne laser for several samples with different reflectivity levels are presented. Comparison with results of conventional measurements is made. The gain from the use of the reflection interferometer is estimated.     

全反射棱镜式环形激光器耦合输出的理论分析

对采用棱镜耦合器的全反射棱镜式环形激光器的耦合输出特性进行了理论研究, 导出了有“楔形”间隙的棱镜耦合器的反射系数和透射系数表达式, 给出了反射率和透过率随“楔形”间隙高度变化的理论计算曲线, 进而研究了有关材料选取、腔内振荡分量的选取及减小棱镜耦合器对环形激光腔内模式的影响等问题. 这些研究对于全反射棱镜式环形激光器在激光陀螺、激光角速度传感器等实际应用中有重要意义.     

非合作目标相位式激光测距中目标漫反射特性的实验研究

阐述了目标的漫反射特性对非合作目标相位式激光测距仪中光功率探测的重要性.设计了一种测量漫反射性能的实验装置,并测量了几种材质的漫反射特性.针对实验结果分析了漫反射特性与不同材质和不同入射角的关系,并指出在其他条件相同时,目标的反射特性还与入射光的波长有关,因此,在选择测距仪的光源时还应考虑被测物表面的反射特性.     

多晶硅表面周期性微结构的激光制备与性能研究

为了减小多晶硅表面入射光的反射率,提高太阳能电池的光电效率,利用紫外纳秒激光器在多晶硅表面制备不同深度、不同间距的微凹坑点阵绒面,研究织构形貌对反射率及光电转换效率的影响。通过激光频率的改变实现微凹坑深度的变化,通过微凹坑排布方式的改变实现微凹坑间距的变化;使用光纤光谱仪测量多晶硅表面反射率并通过激光共聚焦显微镜观察微凹坑形貌;在PC1D软件中建立多晶硅入射光反射模型并模拟不同点阵间距下的多晶硅短路电流和开路电压,计算光电转换效率和填充因子。研究表明,不同频率(300 kHz、200 kHz、150 kHz、50 kHz)和点阵排布方式(300×300、310×310、350×350、400×400)对多晶硅表面的反射率和光电转换效率影响显著,随着频率增大,多晶硅试样反射率先减小后增加最后保持稳定;随着点阵排布密集程度增加,多晶硅试样光电转换效率逐渐提高。实验结果显示当激光频率为150 kHz,点阵分布为400×400时,多晶硅表面微凹坑成型较好,表面平均反射率为3.32%,多晶硅电池的效率为18.80%,相较于未制绒多晶硅电池提高25.9%。     

Shrinkage of picosecond laser beam by plasma reflection in super-resolution near-field structure of SiN/Sb/SiN thin film

The transmittive and reflective Z-scan technique is used with a 10 Hz, frequency doubled, Q-switched, and mode-locked Nd:YAG laser to verify that the reflectivity of the super-resolution near-field structure of an SiN/Sb/SiN thin film increases as incident intensity decreases. This intensity-dependent reflection, called nonlinear reflection, reflects a TEM(00) mode laser beam more strongly at its periphery than at its center and so shrinks the transmitted laser beam. The observed nonlinear reflection is attributed to laser-induced change of carrier densities in Sb, to justify quantitatively the experimental results.     

Optical transmission and reflection of aluminum film irradiated by nanosecond laser beam and experimental studying of phase-explosion

In this paper we present evidence for a phase explosion during the laser-induced ablation process by studying the optical reflectivity of the ablated plume. The ablation was produced by irradiating thin film aluminum coated on a quartz substrate with a single pulse laser beam in ambient air. The laser pulse was provided by the second harmonic of a Q-switched Nd:YAG laser with ∼10 ns pulse duration. The transmission of a low power He–Ne laser beam through the hot ablated material plume and its reflection (from the front surface, and rear surface of aluminum film) were also monitored during the duration of the ablation event. The results show that the front surface reflectivity is enhanced at an early time of ablation which is described as strong evidence for the creation of a phase explosion in this process.     

New Approach to Investigation of Tunable External Cavity Semiconductor Lasers

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Variable reflectivity unstable resonators for a long pulse XeCl excimer laser

The divergence of a long pulse, low gain XeCl excimer laser has been improved using confocal positive branch unstable resonators with variable reflectivity mirrors as outcouplers. With variable reflectivity unstable resonators, nearly diffraction limited beams are obtained. Variable reflectivity resonators lead to high brightness beams (9.1 10 W/(cm sr)). Different reflection profiles were studied with respect to their influence on the beam quality and the energy extraction.     

Magneto-optical Kerr effect in bilayer structures

This paper describes the magneto-optical effects and the reflectivity behaviors of bilayers based on magnetic and isotropic ()/anisotropic () layers under the condition of total internal reflection. In the framework of Green's dyadic technique, we show accurately the optical properties of anisotropic layers deposited on a substrate. We present numerical simulations which account for the variation of angle of incidence at the HeNe laser wavelength. The Kerr rotation is found to increase significantly around the optical modes in total reflection. We also discuss the importance of anisotropic effects due to the crystallization of the dielectric material () which occur in the reflectivity and Kerr rotation spectra. Received 26 January 2000     

玻璃与液晶非线性光学界面反射特性的研究

本文系统地研究了由玻璃与液晶构成的非线性光学界面。用一台调Q的红宝石激光器研究了由玻璃与处于各向同性液相的液晶所构成的非线性界面。在不同入射角时非线性界面由内部全反射跃变到部分透射的阈值光强与Kaplen的平面波理论计算结果相一致。在T-T_c=2.5℃条件下测量了时间分辨的非线性界面的反射率。观察到了反射率的滞后迴线。非线性界面的这种反射率的滞后迴线可以归之于液晶分子退取向的弛豫过程。用Ar⁺激光器研究了玻璃与向列相液晶所构成的非线性光学界面,观察到了由相变而产 关键词：     

Theoretical analysis of widely tunable external cavity semiconductor laser with sampled fiber grating

Combination of equivalent reflection cavity model and transmission line theory is applied in theoretical analysis of external cavity semiconductor lasers with sampled fiber Bragg grating. The effects of device parameters on the resonant cavity mode and the side mode suppression ratio have been discussed. For a perfect anti-coated facet and the high coupling efficiency, it is found that the Vernier effect between combed reflectivity peaks and F-P cavity modes can be destroyed and the laser will work on multi-wavelength. The high coupling efficiency plays the same role as the lower anti-reflection coating reflectivity in the side mode suppression ratio and the mode resonance. Finally, the side mode suppression ratio is investigated in detail depending on the anti-coating reflectivity, the coupling efficiency and the high-reflection coating reflectivity.     

Determination of the reflectivity curve of a spherically bent mica crystal used to diagnose X-ray radiation of relativistic laser plasma

A method for determining the crystal reflectivity curve, based on the use of a broadband X-ray source and an additional spectrometer with preliminarily measured characteristics is proposed. Such a technique does not allow determination of the absolute reflectivity, but makes it possible to measure the dependence of its relative values on the wavelength. Using X-ray radiation of relativistic dense laser plasma, the reflection curve of a spherically bent mica crystal is measured in the range of 6.7–8.7 Å. The obtained reflectivity curve is used to correctly interpret X-ray spectra of dense plasma generated during the interaction a petawatt laser pulse with solid targets.     

Optical feedback cavity ring-down technique for accurate measurement of ultra-high reflectivity

A novel cavity ring-down (CRD) technique, based on the optical feedback effect of Fabry–Perot diode lasers, is developed for accurate reflectivity measurement of highly reflective cavity mirrors. The strong optical feedback, including the direct reflection from the front cavity mirror of a linear ring-down cavity, is re-injected into the oscillator cavity of the diode laser, and large resonant peaks are observed in the ring-down cavity output signals. The diode laser is switched off by a threshold circuit when the amplitude of a resonant peak exceeds a pre-defined threshold. Exponentially decayed signals recorded immediately after switching off the laser are used to determine the cavity decay time. The ultra-high reflectivity of cavity mirrors is measured to be 99.99606% with a reproducibility of 0.00003%. Compared with the previous phase-shift CRD technique, the signal-to-noise ratio of the cavity output signals is improved with an enhancement factor of over 100.     

磁控溅射法制备的高反Ag_5In_5Te_(47)Sb_(33)相变薄膜的光谱性质及短波长静态记录性能

研究了磁控溅射制备的Ａｇ５Ｉｎ５Ｔｅ４７Ｓｂ３３相变薄膜的光谱及短波长静态记录性能。研究结果表明，晶态薄膜反射率较高，并在６００～９００ｎｍ波长范围内，晶态与非晶态的反射率和折射率相差很大。在ＣＤ－Ｅ系统的工作波长７８０ｎｍ处，晶态反射率高达５０％，光学常数为５．３４－１．０ｉ；非晶态反射率为２３％，光学常数为２．５－１．０３ｉ。从这一角度讲，Ａｇ５Ｉｎ５Ｔｅ４７Ｓｂ３３相变薄膜适于做ＣＤ－Ｅ系统的记录介质。另外，采用波长为５１４．４ｎｍ的短波长光学静态记录测试仪对Ａｇ５Ｉｎ５Ｔｅ４７Ｓｂ３３薄膜的记录性能进行了测试，结果表明，这种薄膜短波长记录性能较好，它在较低功率和短脉宽的激光束作用下就可得到较高的反射率对比度。     

激光脉冲诱导的等离子体密度调制及其产生的相位反射

理论研究和数值模拟发现入射光和反射光在低密度等离子体中形成的干涉场可以产生深度的等离子体密度调制. 对于中等强度的入射光，譬如10¹⁵W／cm² ，产生密度调制的时间尺度在几十个光周期的范围. 这样的等离子体密度调制可以起类似布拉格反射镜的 作用，使得后面的入射光在临界面以下的区域产生相位反射. 因为密度调制的周期是光在等 离子体中波长的一半，其产生的反射率可以接近100％. 相位反射也可以在不均匀的低密度 等离子体中产生，它可以极大地减少等离子体对光的吸收，因此在惯性约束核聚变中需要考 虑到它的影响. 关键词： 相位反射 密度调制 激光等离子体 粒子模拟     

4.48 nm正入射软X射线激光用Cr/C多层膜高反射镜的研制

针对4.48nm类镍钽软X射线激光及其应用实验,设计制备了工作于这一波长的近正入射多层膜高反射镜。选择Cr/C为制备4.48nm高反射多层膜的材料对,通过优化设计,确定了多层膜的周期、周期数以及两种材料的厚度比。模拟了多层膜非理想界面对高反射多层膜性能的影响。采用直流磁控溅射方法在超光滑硅基片上实现了200周期Cr/C多层膜高反射镜的制备。利用X射线衍射仪测量了多层膜结构,在德国BessyⅡ同步辐射上测量了在工作波长处多层膜反射率,测量的峰值反射率达7.5%。对衍射仪测量的掠入射反射曲线和同步辐射测量的反射率曲线分别进行拟合,得到的粗糙度和厚度比的结果相近。测试结果表明,所制备的Cr/C多层膜样品结构良好,在指定工作波长处有较高的反射峰,达到了设计要求。