激光器与轨道的相对位置对动态加热的影响

 通过分析光束入射的角度因子将激光器在地平面上的安放位置进行分类,采用了几何分析和数值模拟的方法,探讨了聚焦激光束在加热运动圆柱体过程中,为了达到一定的加热功率水平和能量水平以取得最好的加热效果而应采取的措施,即应当以激光垂直入射的轨道点为中心,以激光的有效工作时间为取值范围,并参考大气对激光能量的衰减,相对于轨道选取适当的距离进行加热。该研究从理论上说明了激光器与圆柱体运动轨道的相对位置对激光动态加热的影响可以看作一个优化问题,存在最优解,进而对于合理使用激光器进行动态加热具有参考价值。     

一种大功率窄脉冲半导体激光器测试台的研制

大功率窄脉冲半导体激光器主要光电性能参数为:输出峰值光功率、阈值电流、正向电压、上升时间、峰值波长、光谱半宽、半强度角.根据激光制导系统对大功率窄脉冲激光器参数的特殊测试要求,研制一种大功率窄脉冲激光器测试平台,将小型化大功率激励器功放模块、大范围可调DC-DC模块、信号源板、激光器座、光学准直镜集成在一个平台上,与峰值功率计、光谱仪、CCD摄像机等仪器配合,可测出大功率窄脉冲激光器的峰值功率、峰值波长及波长随温度变化的漂移特性、发光芯均匀性等参数.介绍了大功率窄脉冲激光器测试台的特点,并对测试结果作了论述.     

Effect of a prepulse on ablation-pressure smoothing in laser heating of thin foils

The results of theoretical and experimental studies of plasma heating by nonuniform laser radiation and the symmetrizing effect of a laser prepulse on the uniformity of heating of thin foils, which simulated thin-shell laser inertial-confinement fusion (ICF) targets, are presented. The high efficiency of symmetrization by a prepulse was demonstrated both experimentally and theoretically. __________ Translated from Preprint No. 16 of the P. N. Lebedev Physical Institute, Moscow (2006).     

Synthesis experiments on in-Sb and B-Sb systems in a laser heated diamond-anvil cell

Abstract

High pressure and high temperature synthesis experiments were carried out on In-Sb and B-Sb systems with a laser heated diamond-anvil cell. InSb was synthesized starting from In and Sb at various pressures ranging from 0.2 to 10 GPa. The cubic as well as the high pressure phases were successfully synthesized. Experiments above 8 GPa, wherein antimony exists in the tetragonal phase, have revealed no new phases of InSb. Trials of synthesizing a compound from B and Sb gave negative result to at least 30 GPa.     

用于高能激光系统的共孔径光学装置设计

高能激光系统的主要工作方式是利用其精跟踪模块将发射激光传输聚焦至闭环跟踪条件下的目标上,使之受到毁伤或失效。为实现该工作方式,本文研究设计了一套共孔径光学收发装置。该装置的发射系统主要由离轴两反式主望远镜模块、伽利略透射式调焦望远镜模块和光束馈送模块共同组成二级扩束系统,接收系统主要由离轴两反式主望远镜模块、精跟踪成像模块和光束馈送模块共同组成长焦距光学系统,其中光束馈送模块由二向色镜、快速反射镜等光学元件组成。以非相干空间合束的基模高斯光作为激光光源,利用光学设计软件对该装置进行了优化设计。对于发射系统,获得了激光经过调焦望远镜模块不同的调焦量调制后,传输至0.5~5 km处的光斑分布情况,且激光波前像差RMS值均优于λ/20;对于接收系统,由各模块一同构成的成像光学系统的性能经优化后接近衍射极限,其中系统传递函数在70 lp/mm时大于0.6,最后通过样机实验也验证了设计的正确性。本文的设计和实验结果证实了该共孔径光学收发装置结构合理,性能可靠,满足高能激光系统的工程应用需求。     

线结构光传感器中非线性光源单向扩展光路设计

为了减小线结构光传感器光源对测量精度的影响 ,设计了一种集整形和能量校正为一体的非线性光源单向扩展光路。应用反高斯分布的液体吸收滤光镜 ,实现了高斯光束强度的径向均匀化。并应用矩形光阑和两个相互垂直放置的柱面镜 ,对准直后的激光束进行整形 ,分别在不同的方向进行拉伸和压缩 ,得到了形状理想的线光源。此技术已成功应用于BGA芯片管脚的三维尺寸测量中。     

Temperature prediction for CO2 laser heating of moving glass rods

This paper presents a heat transfer model to calculate the temperature field in moving glass rods heated by a CO₂ laser. Conduction and radiation heat transfer in radial and axial directions are taken into account in the current model. The Rosseland diffusion approximation is incorporated to analyze the radiation heat transfer in the glass rod. A two-band model is used to simulate the spectral property of the glass. Results of the simulation show that glass rods of sufficiently large optical thickness should be treated as a semitransparent medium for radiative transfer, and it is reasonably accurate to assume it to be opaque to CO₂ laser irradiation. It has been shown that the resulting temperature profile is strongly dependent on the laser parameters, i.e., the size of laser beam and the power of the laser. The diameter and speed of the moving glass rod are also important in determining the temperature field although the convective heat transfer coefficient between the glass rod and the environment has little effect.     

Gaussian optical design of a submillimeter-wave and far-infrared laser sideband heterodyne spectrometer

A submillimeter-wave/far-infrared (SMM/FIR) laser sideband heterodyne spectrometer has been built for molecular rotational spectroscopy application in the frequency range of 600–3000 GHz. Based on Gaussian optics, optical system of the spectrometer is designed to be quasi-achromatic and low losses. In this article the optical design and the performance of the spectrometer are presented.     

Achievements in high‐pressure science at the high‐brilliance energy‐dispersive X‐ray absorption spectrometer of ESRF,ID24

Although the idea of an X‐ray absorption spectrometer in dispersive geometry was initially conceived for the study of transient phenomena, the instrument at the European Synchrotron Radiation facility has been increasingly exploited for studies at extreme conditions of pressure using diamond anvil cells. The main results of investigations at high pressure obtained at beamline ID24 are reviewed. These concern not only fundamental topics, such as the local and the electronic structure as well as the magnetic properties of matter, but also geological relevant questions such as the behaviour of Fe in the main components of the Earth's interior.     

Laser heating in diamond anvil cells: developments in pulsed and continuous techniques

Developments in continuous and pulsed laser‐heating techniques, and finite‐element calculations for diamond anvil cell experiments are reported. The methods involve the use of time‐resolved (5 ns gated) incandescent light temperature measurements to determine the time dependence of heat fluxes, while near‐IR incandescent light temperature measurements allow temperature measurements to as low as 500 K. Further optimization of timing in pulsed laser heating together with sample engineering will provide additional improvements in data collection in very high P–T experiments.     

Analytical solution for multilayer assembly including heating and cooling cycles with laser pulse parameter variation

Laser heating of surfaces is involved with heating and cooling cycles. Material response to a laser pulse in the heating cycle is rapid while in the cooling cycle it is gradual. In this case, temperature rises rapidly in the heating cycle while temperature decay is gradual in the cooling cycle. Depending on the laser pulse properties (pulse length and intensity), the rise and fall of temperature profiles change in the surface region of the substrate material. In the present study, an analytical solution for laser heating pulse is presented and a closed-form solution for temperature distribution inside the multilayer assembly is obtained. Steel is considered as top layer while copper is situated below steel in the multilayer assembly. It is found that the analytical solution agrees well with the numerical predictions. Temperature rise in steel is higher than copper. This is due to the thickness of steel, which is larger than the absorption depth. In this case, internal energy gain dominates over the heat conduction in the energy transport process.     

激光二极管泵浦的重复频率大能量低温Yb:YAG激光器设计

为实现重复频率大能量激光输出,基于Yb:YAG激光介质低温下良好的热特性和激光特性,设计了12kW高功率激光二极管(LD)阵列泵浦的V型腔低温Yb:YAG激光器(液氮温度)。对于泵浦耦合系统和散热结构两个关键点,分别使用光线追迹方法和有限元方法进行了分析,提出了楔形真空窗口和低温热管等解决方案。模拟结果表明,该设计的激光器热效应较低,可实现重复频率大能量输出。     

基于Polytec激光测振仪的光存储设备振动测试分析系统

针对光存储设备振动频率高的特点,采用Polytec激光测振仪拾取振动信号,并给出了基于Polytec激光测振仪的光存储设备振动测试分析系统。可用于硬盘盘片、磁头滑块、折臂组件、光盘盘片等振动测试,为光存储设备动态特性的测试和分析建立了良好的实验基础。     

成像与激光发射系统的共口径设计与实验

将成像光学系统同时用作激光发射天线的共口径设计可有效减轻卫星载荷质量和应对各种突发状况。首先根据激光通信的能量计算链路,分析了激光发射天线的设计要求,明确了激光发射天线与成像光学系统的不同;然后根据特定的成像光学系统给出了3种具有普适性的共口径设计方法,并对这3种方法的性能进行了分析和比较,给出了它们的优缺点和适用范围;最后对所设计的共口径系统进行了发射光束仿真,经过对设计系统加工、装调后进行了室内的成像、通信实验,结果显示发射激光的最小束散角可达18.2 μrad,接近系统衍射极限,出射光斑质量良好,接收到的图像与成像系统所成图像肉眼观测无失配。初步证实该共口径设计可实现光学系统的成像和通信任务要求。     

激光核聚变与高功率激光:历史与进展

回顾激光聚变近50年来的发展历程,评述聚变物理与高功率激光驱动器的研究进展,展望聚变能源未来前景.     

激光核聚变与高功率激光：历史与进展

回顾激光聚变近50年来的发展历程,评述聚变物理与高功率激光驱动器的研究进展,展望聚变能源未来前景.     

A reaction cell with sample laser heating for in situ soft X‐ray absorption spectroscopy studies under environmental conditions

A miniature (1 ml volume) reaction cell with transparent X‐ray windows and laser heating of the sample has been designed to conduct X‐ray absorption spectroscopy studies of materials in the presence of gases at atmospheric pressures. Heating by laser solves the problems associated with the presence of reactive gases interacting with hot filaments used in resistive heating methods. It also facilitates collection of a small total electron yield signal by eliminating interference with heating current leakage and ground loops. The excellent operation of the cell is demonstrated with examples of CO and H₂ Fischer–Tropsch reactions on Co nanoparticles.     

Probing the local,electronic and magnetic structure of matter under extreme conditions of temperature and pressure

ABSTRACT

In this paper we present recent achievements in the field of investigation of the local, electronic and magnetic structure of the matter under extreme conditions of pressure and temperature. These results were obtained thanks to the coupling of a compact laser heating system to the energy-dispersive XAS technique available on the ID24 beamline at the ESRF synchrotron. The examples chosen concern the melting and the liquid structure of 3d metals and alloys under high pressures (HPs) and the observation of temperature-induced spin crossover in FeCO₃ at HP.     

Design and fabrication of an optimum holographic optical element lens for a femtosecond laser pulse using a hologram computer-aided design tool

Design and fabrication of an optimum holographic optical element (HOE) lens for a femtosecond laser pulse using a hologram computer-aided design (CAD) tool is presented. The hologram CAD tool, which the authors have developed can design, analyze, and evaluate holograms fabricated by interferometrical technique. The function of the tool is extended to design and analyze a HOE lens illuminated with a femtosecond laser pulse. An optimum HOE lens for a laser pulse, which has 130 fs duration, 720 nm central wavelength, and 10 nm spectrum bandwidth, is designed by the tool. The optimum HOE lens gives both high diffraction efficiency and small amount of aberration. The designed HOE lens is fabricated and its optical characteristics have been experimentally evaluated. The reconstructed point images agree with the results of the numerical simulations by the tool. The tool demonstrates the capability of designing the optimum HOE lens for a femtosecond laser pulse.     

Frequency-domain fluorescence lifetime imaging for endoscopic clinical cancer photodetection: Apparatus design and preliminary results

We describe a new fluorescence imaging device for clinical cancer photodetection in hollow organs in which the tumor/normal tissue contrast is derived from the fluorescence lifetime of endogenous or exogenous fluorochromes. This fluorescence lifetime contrast gives information about the physicochemical properties of the environment which are different between normal and certain diseased tissues. The excitation light from a CW laser is modulated in amplitude at a radio frequency by an electrooptical modulator and delivered by an optical fiber through an endoscope to the hollow organ. The image of the tissue collected by the endoscope is separated in two spectral windows, one being the backscattered excitation light and the other the fluorescence of the fluorochrome. Each image is then focused on the photocathode of image intensifiers (II) whose optical gain is modulated at the same frequency as the excitation intensity, resulting in homodyne phase-sensitive images. By acquiring stationary phase-sensitive frames at different phases between the excitation and the detection, it is possible to calculate in quasi-real time the apparent fluorescence lifetime of the corresponding tissue region for each pixel. A result obtained by investigating the endogenous fluorochromes present in the mucous membrane of an excised human bladder is presented to illustrate this method and most of the optical parameters which are of major importance for this photodetection modality have been evaluated.