基于激光掩星吸收光谱的二氧化碳探测技术

本文分析了固定波长激光掩星差分吸收技术的优点和不足,介绍了可调谐激光直接吸收光谱技术测量原理.分析了最优波长透过率与信噪比的关系以及测量误差与背景光干扰的关系.根据高灵敏度探测器的工作波长范围,选择了6310.915 cm?1、6310.893 cm?1、6310.890 cm?1、6310.8834 cm?1作为吸收...     

ns激光辐照硅光电探测器的损伤阈值

以He-Ne激光作为参考光,采用反射光能量法,测量了ns激光辐照硅光电探测器的损伤阈值,并测量了不同功率密度的强激光辐照下探测器对参考光的反射率.实验结果表明,ns激光辐照硅光电探测器的损伤阈值为4.1×106W/cm2,在探测器被强激光损伤的初期阶段,探测器对参考光的反射率下降很快,继续增加入射激光的能量,探测器对参考光的反射率下降趋于平缓.     

基于星地测量和辐射传输模式的特定地域大气中分辨力光谱辐射特征

 利用中分辨力成像光谱仪数据,采用星地测量并结合中分辨力辐射传输模式,以巢湖流域及周边为实验区,计算得到该地区夏季实际大气层结下沿观测路径整层大气透过率、大气辐射、大气热辐射和大气散射的太阳辐射在中分辨力光谱上的特征,以及整层大气廓线。研究结果表明：受能见度影响,实验区两地点水体像元处的整层大气透过率数值略高于植被像元处;两地卫星入瞳处的程辐射和卫星探测器探测到的程辐射谱分布相似;在可见至近红外波段,大气程辐射和散射的太阳辐射谱分布相似性较强,且随着波长增加而数值均逐渐减小,而大气热辐射数值很小;两个地点在短波范围内路径热辐射很低且接近,随着波长的增加,热辐射明显增强,波长越长,两地点热辐射差别越明显;当日天气晴好,气溶胶含量较低,而且两地距离很近,因此两地的大气廓线数据基本相似。     

激光对反舰导弹红外探测器干扰分析

针对激光对红外制导的反舰导弹干扰问题,建立了激光对反舰导弹红外探测器的干扰链路模型,推导了激光海上传输的大气透过率,计算了1．06μm激光在海上大气传输时仰角、能见度与大气透过率的关系,估算了对不同距离的反舰导弹红外探测器实现有效干扰所需发射的激光能量。     

面向光学器件透反射率测量的声光调制型激光功率稳定系统设计

在各类光学系统设计过程中,由于实验系统对于光学器件的透反射率要求不同,需要确定光学器件的透反射率。本文设计了一种对光学器件的透反射率进行精准测量及标定的系统,该系统通过对激光光源进行声光调制,使得激光输出功率的稳定度显著提高,避免了测量时光源不稳定带来的较大误差。实验结果表明,该系统能够稳定光源输出功率,稳定度维持在0.05%/h,甚至更高的水平,满足了光学器件透反射率测量的误差小,精度高等要求。     

一种测量光学元件高反射（透过）率的有效方法

本文提出一种测量激光谐振腔反射镜高反射率和测量镀有减反膜的高透过率光学元件的有效方法.特点是同时测量几块高反射率凹面镜或高透过率光学元件,其误差是普通单块测量方法的1/n.详细分析了一组激光腔镜高反射率和一组镀减反膜的平行薄片高透过率的测量结果.     

雾对无线激光通信系统的影响

从雾的物理特性出发,对激光在雾媒质中的传播衰减特性进行了理论研究。分别给出了无线激光通信系统的信号模型、噪声模型和透过率,并给出了不同激光波长、能见度、测量距离和接收器视场角对无线激光通信系统的影响。最后,以工作波长为10.6μm的激光为例,利用衰减率与透过率之间的关系,给出了平流雾及辐射雾中激光雾衰减随能见度、接收器视场角等的变化关系。数值分析表明：激光波长、雾的能见度、测量距离和接收器视场角对无线激光通信系统均有较大的影响。     

红外探测系统的激光辐照热效应仿真分析

为研究红外探测系统受激光辐照后的热效应与二次热辐射对探测器成像的影响,使用Ansys软件对红外探测器进行热辐射仿真和有限元结构仿真;采用黑体辐射定律和DO辐射计算模型模拟计算探测器内光学系统在不同激光辐照度下的温度随时间变化情况以及探测器内部温升对靶面成像的二次热辐射干扰情况;采用热弹性力学模型仿真计算探测器内部的热应力和热变形情况。结果表明:探测器受到1.06μm激光照射,矫正镜激光辐照度在50 W/cm²时,靶面受到二次热辐照度在0.6 s时达到100μW/cm²的量级,使红外探测器达到饱和;探测器受激光辐照后系统最高温度出现在矫正镜中心处,拟合得到系统最高温度与受照时间函数关系,可预测探测器升温结构破坏;最大热变形出现在矫正镜背面中心处,由外向内形成不等附加光程差,干扰探测器的成像效果;最大热应力出现在矫正镜前面中心处,得到最大热应力与激光辐照度间的线性关系曲线,为矫正镜热应力破坏提供预测参数。     

固定波长激光直接吸收方法同时测量高温CO气体的温度与浓度

针对可调谐半导体激光吸收光谱技术(TDLAS)需要在整个谱线上扫描导致扫描过程中可能存在其他谱线干扰以及测量速度较慢的问题,提出了固定波长激光直接吸收测量方法。该方法采用固定波长下的直接吸收计算气体浓度,完全避免了谱线干扰的问题,并且提高了测量速度,尤其适合于动态燃烧化学反应的研究。通过在气体吸收池中对不同工况下的CO气体的温度以及浓度进行了测量,验证了方法的准确性,说明这种固定波长激光直接吸收测量方法同TDLAS方法一样可以应用于气体浓度和温度的测量。     

ESR膜及在POLAR探测器中的应用

基于巨双折射光学的增强型镜面反射膜(ESR)具有高分子多层膜结构。在10~80°反射角范围内,利用623.8nm,532nm,441.6nm和413.1nm激光对ESR的反射率进行了测量,结果显示,在整个范围内有较均匀的反射率,平均反射率大于95%,平均透过率小于0.5%。XRD分析显示ESR在大尺度范围内有良好的晶化结构。在γ射线极化仪POLAR应用中,ESR作为BC448塑料闪烁体探测器反射层比用黑漆反射层的光子收集效率提高了近10倍。     

温度和压力对Au反射特性影响及动高压下的测温应用分析

基于金属电子气模型,进行了温度、压力对Au反射率变化影响的研究与分析。利用DAC装置开展了压力对Au反射率变化测量实验,以及激光加热的动态温升条件下温度对Au反射率变化测量实验,获得了探测光束波长为488 nm条件下,温度(室温至350 ℃)和压力(11 GPa范围内)对Au反射特性影响的实验结果。结果表明:在11 GPa压力范围内,与温度因素相比,压力对Au的反射率变化影响可忽略;Au对488 nm波长激光的反射率变化趋势为单调递增,变化幅值达约10%,且具有反射率与温度的一一对应特性。通过动高压加载下材料温度瞬态测量要求分析,认为基于Au在488 nm波长下的反射变化特性,可建立一种适用于动高压加载下低温段(低于1000 K)的瞬态测温方法,用于解决材料动高压领域的瞬态测温技术难点。     

Optical properties of a new IR converter for laser beam analysis

This work presents the temporal and spacial resolution of a new infrared (IR) converter based on thermal radiation emission. Using this converter, it is possible to measure the intensity distribution of laser beams with a wavelength between 1 and 20 μm. For this purpose, the laser radiation (for example, 10.6 μm) is converted into a wavelength coverage of 800–1100 nm. In the actual converter thin metal foils provide the basis of this method. The metal foils are heated to a temperature of 600–800 K. The emitted radiation of the foils defers into the near-infrared (NIR) area, thus enabling detection by camera systems based on silicate. Additional heat input of the laser results in a local temperature increase, and then the increase in radiation intensity can be measured. Typical thicknesses of converter metal foils are <5μm. Foil materials with a low thermal conductivity, good absorption of the measured laser beams, and a high melting temperature are particularly suitable. These parameters are well shown by using stainless steels, such as INOX (stainless steel 1.4310 CrNi steel). Using this material, it is possible to gain a maximum spatial resolution of 250 μm and a temporal resolution of 12.5 Hz, by a measurement range from 1 to 100 W/cm². The maximum measured intensity is 125 W/cm².     

Optical-pyrometric diagnostics of the state of silicon during nanopulsed laser irradiation

The dynamics of the reflectivity at ?? = 0.53 ??m and the IR radiation of silicon in the wavelength range 0.9?C1.2 ??m is studied under the action of nanosecond ruby laser radiation pulses. When radiation energy density W is lower than the threshold of laser-induced melting of the surface of a semiconductor crystal, the major contribution to the IR radiation emitted by this crystal is made by edge photoluminescence. As the melting threshold is exceeded, the nanosecond dynamics of the detected IR radiation changes from photoluminescence to the thermal radiation of the forming Si phase melt with a high reflectivity. The results of pyrometric measurements of the peak melt surface temperature as a function of W obtained at an effective wavelength ?? _e = 1.04 ??m of the detected IR radiation agree with the data of analogous measurements performed at ?? _e = 0.53 and 0.86 ??m.     

飞秒激光抽运探测热反射法对金属纳米薄膜超快非平衡传热的研究

随着微电子器件尺寸的减小、 工作频率的提高, 金属薄膜中电子与声子将处于非平衡状态, 这将导致微电子器件的热阻增大. 为准确地对这些微电子器件进行热管理, 电子-声子耦合系数的测量变得越来越重要. 本文采用飞秒激光抽运-探测热 反射法研究了不同厚度的金属纳米薄膜的非平衡传热过程. 通过抛物两步模型对实验数据进行拟合, 在拟合过程中引入电子温度与声子温度对反射率影响的比例关系, 从而优化了拟合结果. 通过对不同厚度的Ni膜与Al膜的电子-声子耦合系数的研究, 表明金属薄膜中的电子-声子耦合系数并不随薄膜厚度的改变发生变化. 实验结果还验证了探测光的反射率同时受到电子温度和声子温度的影响, 并通过数据分析量化了电子温度和声子温度对反射率的影响系数.     

基于激光旋转加热的非导电材料高温光谱发射率测试方法与装置

光谱发射率是表征材料热物理性能的重要参数。对于非导电材料的高温光谱发射率测试,一般采用高温加热炉加热或辐射加热的方式来进行发射率测试,存在的问题是采用高温石墨炉加热时,样品可能会与高温石墨发生化学反应,从而破坏材料原有物性;采用辐射加热,一般是单向静止加热,会存在样品温场梯度非均匀分布的问题。基于激光旋转加热和样品/黑体整体一体化设计,提出了一种“样品动中测”的非导电材料高温光谱发射率测试新方法,建立了相应的测量模型,突破了传统的 “样品静中测”的局限,样品与参考黑体共形一体化设计,采用微区域光谱辐射成像方法,同时测量参考黑体和样品的光谱辐射能量与温度。建立了激光旋转加热状态下的热传导方程,对典型样品材料的温度分布进行了仿真计算,结果表明旋转样品温场分布较为均匀,分析了温场分布与红外光谱发射率测量误差间的关系,给出了适用于本测试方法的材料的热导率下限值。基于该方法,搭建了相应的测量装置,对典型材料碳化硅在1 000 K时的光谱发射率进行了测试,在4 μm处对各个典型高温温度点的光谱发射率进行了测试,得到了碳化硅材料在红外波段的光谱发射率波长变化和温度变化规律特性。与国外的测量结果进行了比对,结果较为一致,验证了激光旋转加热光谱发射率测试方法的可行性。采用此方法,不破坏样品本身的理化特性,样品加热升温速度快,测量温度范围上限高,有效减小了激光静止单向加热带来的温度不均匀性,可同时测量出样品和参考黑体的光谱辐射亮度及温度,无需另外再设计标准高温黑体,解决了现有非导电材料高温光谱发射率测试中非均匀加热和辐射能量同步比对测量的问题,可应用于多种非导电材料高温光谱发射率的测试。     

Nanosecond-time-resolution thermal emission measurement during pulsed excimer-laser interaction with materials

A nanosecond-time-resolution pyrometer has been developed for measuring the transient surface temperature of a solid material heated by pulsed excimer-laser irradiation. Fast germanium diodes are employed to capture the transient thermal emission signals in the wavelength range between 1.2 and 1.6 pm. The surface temperature is derived from the measured spectral thermal emission. The directional spectral emissivity is determined in situ by measuring the transient directional spectral reflectivity and applying Kirchhoffs law. The experimental results are in good agreement with numerical thermal modeling predictions. The pyrometric thermal emission measurement also yields the solid/liquid interface temperature during the pulsed excimer-laser-induced melting. The relation between the measured interface superheating temperature and the interface velocity reveals the melting kinetic relation during the high-power, short-pulse laser-induced phase-change processes.     

3D features of modified photostructurable glass-ceramic with infrared femtosecond laser pulses

The exclusive ability of laser radiation to be focused inside transparent materials makes lasers a unique tool to process inner parts of them unreachable with other techniques. Hence, laser direct-write can be used to create 3D structures inside bulk materials. Infrared femtosecond lasers are especially indicated for this purpose because a multiphoton process is usually required for absorption and high resolution can be attained. This work studies the modifications produced by 450 fs laser pulses at 1027 nm wavelength focused inside a photostructurable glass-ceramic (Foturan^®) at different depths. Irradiated samples were submitted to standard thermal treatment and subsequent soaking in HF solution to form the buried microchannels and thus unveil the modified material. The voxel dimensions of modified material depend on the laser pulse energy and the depth at which the laser is focused. Spherical aberration and self-focusing phenomena are required to explain the observed results.     

Transient heat transfer in a spherical protective material, submitted to flux and mixed boundary conditions: an investigation on zirconia

An analytic solution is presented for describing combined radiation and conduction heat transfer in a spherical fiber thermal protection exposed to combined radiative and convective heating. The solution includes the equation of radiative transfer within the material, coupled to a transient energy equation that contains both radiative and convective terms. At elevated temperatures radiative transfer becomes important, and if several hot surfaces view each other, the radiation exchange process must be considered carefully. Some thermal protections are partially transparent to thermal radiation. Hence, an exchange process is complicated by radiation penetrating into and coming out of material. The radiation leaving an area depends on the temperature distribution inside that area and that is unknown and is affected by the exchange process to other areas. The analysis has allowed for unlimited spectral detail but assumes that the various material properties do not vary significantly with temperature. Transient temperature distributions are obtained for the boundary conditions of external radiation and convection. The present analysis includes the influence of reflectivity, surface radiative properties and spectral properties on the temperature distributions.     

Characteristics of high power diode laser removal of multilayer chlorinated rubber coatings from concrete surfaces

This paper reports the technical feasibility and process characteristics of removing chlorinated rubber (CR) coatings from concrete surfaces utilising a 60 W continuous wave (cw) diode laser operating at 810 nm wavelength. Coating layers of various thickness have been removed under an oxygen shroud-gas, as well as Ar and N₂. Optical microscopy and energy dispersive analysis of X-rays (EDX) have been utilised to verify this. The reflectivity properties of the CR material from the visible to the near infrared wavelengths, as well as their behaviour under high temperatures have been examined with a normal incidence spectrometer and a differential thermal analysis/thermal gravimetric analysis (DTA/TGA) system. The resulting drop in reflectivity explains the possibility of sustaining the combustion, even though the reflection coefficient of white CR at 810 nm is almost 100%.     

Nanosecond-time-resolution thermal emission measurement during pulsed excimer-laser interaction with materials

A nanosecond-time-resolution pyrometer has been developed for measuring the transient surface temperature of a solid material heated by pulsed excimer-laser irradiation. Fast germanium diodes are employed to capture the transient thermal emission signals in the wavelength range between 1.2 and 1.6rwm. The surface temperature is derived from the measured spectral thermal emission. The directional spectral emissivity is determined in situ by measuring the transient directional spectral reflectivity and applying Kirchhoff's law. The experimental results are in good agreement with numerical thermal modeling predictions. The pyrometric thermal emission measurement also yields the solid/liquid interface temperature during the pulsed excimer-laser-induced melting. The relation between the measured interface superheating temperature and the interface velocity reveals the melting kinetic relation during the high-power, short-pulse laser-induced phase-change processes.