半导体激光器自混合效应对连续光腔衰荡技术的影响

根据光腔衰荡(CRD)原理开展了高反镜反射率测量技术的研究.采用基于半导体激光器自混合效应的连续光腔衰荡技术(SM-CRD)测量高反射率腔镜,不但简化了CRD技术应用的结构装置,同时也大大提高了入射光与衰荡腔之间的耦合效率.给出了半导体激光器由于自混合效应引起的频谱变化,分析了反馈光强度对半导体激光器输出特性的影响.使用反射率为99.914%的腔镜建立了1 064 nm高反射率测量装置,测量精度达到10-5量级.实验结果表明,使用该装置测量腔镜的反射率,不但大大降低了系统的成本,而且有利于提高系统的测量精度和稳定性.     

Sagnac效应在连续波腔衰荡微量气体浓度测量系统中的应用

基于环形光路的Sagnac效应及腔衰荡测量技术原理,本文提出了一种新型的连续波腔闲置不用衰荡微量气体浓度测量系统.系统中利用环形光路的Sagnac效应,将光纤环作为一个等效反射镜,与高反射率镜形成衰荡腔,实现衰荡腔的反射率可调,从而降低系统对入射光强度的要求,对信号处理提供了条件.在此基础上,文中对环形光路Sagnac...     

利用腔内凹面镜控制输出光束稳定性的激光系统

本文给出了一种控制正支共焦非稳腔输出光束稳定性的激光系统.利用哈特曼波前传感器实时测量谐振腔内的倾斜扰动像差,基于该像差信号,采用一台步进电机作为主控器,并采用比-积分一微分(PID)控制算法控制一块高反射率的凹面腔镜完成腔内倾斜扰动的自动校正.理论和实验研究表明:本系统能够快速稳定地控制正支共焦非稳腔失调引起的倾斜像差,实现正支共焦非稳腔输出光束的自动稳定.     

基于非本征F-P干涉技术的全光纤位移测量系统北大核心CSCD

为解决传统分离镜组式干涉仪体积较大,无法在空间受限的环境条件下应用的问题,开展了全光纤F-P干涉位移测量技术研究。根据干涉原理分析了不同反射率条件对干涉信号形式的影响,计算得出:当反射率为4%时,多光束干涉的光强信号将近似为正弦函数,并利用有限元仿真对位移测量原理进行验证。设计搭建了基于非本征F-P干涉技术的全光纤位移测量系统。实验结果表明:该系统在1 min内静态噪声电压标准差为23.3 mV;在1 mm位移范围内,该系统与XL-80激光干涉仪的测量结果呈现高度线性关系,线性相关系数R 2为1,且该系统位移测量重复性优于XL-80激光干涉仪。     

高效率二极管端泵浦Nd∶YAG连续激光器

文中介绍了高效率二极管端泵浦 Nd∶ YAG连续激光器。用准连续 1W激光二极管作泵浦源 ,激光工作介质为5 mm× 5 mm的 Nd∶ YAG棒。谐振腔为典型平凹腔 ,输出镜为凹面镜 ,研究了几种不同反射率和不同曲率半径的输出镜对输出功率的影响。得出最佳反射率 98.3% ,最佳曲率半径 15 5 .6 mm,最大输出功率 2 4 4 .4 m W,光 -光效率 4 2 .1% ,斜效率 6 2 % ,腔长 37.4 mm     

基于伺服驱动的离心式动态力校准装置

为提高准静态环境使用的力传感器校准精度,研制了基于伺服驱动的离心式动态力校准装置。该装置利用直驱伺服电机驱动和控制质量块做离心运动,通过去轴承设计的动力传动机构输出量值可控的动态力;建立了动力学模型并得到了实验验证;进行了测量重复性和动态响应性能实验研究。实验结果表明,校准装置在中高转速下测量重复性优于1%,能在0.242s内加速到额定转速500r/min,且输出力值可达到3.8kN。     

光纤光栅肘关节角度测量方法

为解决现有关节角度测量装置的不足,提出一种基于多光纤布拉格光栅(fiber Bragg grating, FBG)的关节角度测量方法。该方法将多光纤光栅固定在套袖上,套袖戴在肘关节上,辅以自主设计的基于LabVIEW关节角度计算及数据处理的程序和可视化界面,实现对肘关节角度实时测量并输出可视化数据。该套袖具有柔性化程度高、不受电磁信号干扰、测量效率高、结构简单的优点。对所制作套袖进行测量实验,实验结果表明,该测量方法的误差约为2.88%,重复性误差在4%以下,具有实际的应用价值。     

激光器全反射介质膜的制作原理与光学厚度测定

阐述了光学薄膜的镀制原理、反射率推算,阐述了镀制全反射介质薄膜过程中光学厚度的测定方法-极值法测量的原理和所用光线的波长,阐述了得到高反射率的条件,给出了测量膜厚的实验系统装置,并叙述了镀制17层全反射介质薄膜的过程和测量的方法,最后给出了17层全反射介质薄膜的反射率测量结果。     

基于端面镀膜的Fabry-Perot光纤传感器研究

应用模式耦合理论计算了外腔式Fabry-Perot（F-P）干涉型光纤传感器的输出光强与F-P腔长的关系。对组成F-P腔的光纤端面进行了磨平抛光及镀多层电介质膜处理，使光纤端面反射率为70%，从而提高了传感器的抗干扰能力，简化了探测系统。将该传感器与电阻就变片作对比测量实验，其结果完全一致。     

高精度零件热变形量测量系统

设计了一种高精度测量零件受热变形量的实验装置.用恒温箱控制温度变化及保持温度稳定,利用电感测头对测量进行定位;同时,利用双频激光干涉仪对电感测头间距离进行精确测量,测头间的距离就是零件的受热变形量.理论分析和实验结果表明,这一系统具有较高的温度控制精度和测量精度.利用该系统对直径为50 mm的圆柱类零件在稳态均匀温度场中相同温度变化下的直径热变形量进行了5次重复性测量,其重复性误差为0.5μm.     

Liquid-phase broadband cavity-enhanced absorption spectroscopy measurements in a 2 mm cuvette

A novel implementation of broadband cavity enhanced absorption spectroscopy (BBCEAS) has been used to perform sensitive visible wavelength measurements on liquid-phase solutions in a 2 mm cuvette placed at normal incidence to the cavity mirrors. The overall experimental methodology was simple, low cost, and similar to conventional ultraviolet-visible absorption spectroscopy. The cavity was formed by two concave high reflectivity mirrors. Three mirror sets with nominal reflectivities (R) of R = 0.99, 0.9945, and 0.999 were used. The light source consisted of a high intensity red, green, blue, or white LED. The detector was a compact charge-coupled device (CCD) spectrograph. Measurements were made on the representative analytes, Ho(3+), and the dyes brilliant blue-R, sudan black, and coumarin 334 in appropriate solvents. Cavity enhancement factors (CEF) of up to 104 passes for the high reflectivity mirrors were obtained. The number of passes was limited by relatively high scattering and absorption losses in the cavity, of approximately 1 x 10(-2) per pass. Measurements over a wide wavelength range (420-670 nm) were also obtained in a single experiment with the white LED and the R = 0.99 mirror set for Ho(3+) and sudan black. The sensitivity of the experimental setup could be determined by calculating the minimum detectable change in the absorption coefficient alpha(min). The values ranged from 5.1 x 10(-5) to 1.2 x 10(-3) cm(-1). The limit of detection (LOD) for the strong absorber brilliant blue-R was 620 pM. A linear dynamic range of measurements of concentration over about two orders of magnitude was demonstrated. The overall sensitivity of the experimental setup compared very favorably with previous generally more experimentally complex and expensive liquid-phase cavity studies. Possible improvements to the technique and its applicability as an analytical tool are discussed.     

Towards High Accuracy Reflectometry for Extreme-Ultraviolet Lithography

Currently the most demanding application of extreme ultraviolet optics is connected with the development of extreme ultraviolet lithography. Not only does each of the Mo/Si multilayer extreme-ultraviolet stepper mirrors require the highest attainable reflectivity at 13 nm (nearly 70 %), but the central wavelength of the reflectivity of these mirrors must be measured with a wavelength repeatability of 0.001 nm and the peak reflectivity of the reflective masks with a repeatability of 0.12 %. We report on two upgrades of our NIST/DARPA Reflectometry Facility that have given us the ability to achieve 0.1 % repeatability and 0.3 % absolute uncertainty in our reflectivity measurements. A third upgrade, a monochromator with thermal and mechanical stability for improved wavelength repeatability, is currently in the design phase.     

Analytical method to find the optimal parameters for gas detectors based on correlation spectroscopy using a Fabry-Perot interferometer

Several designs of infrared sensors use a Fabry-Perot interferometer (FPI) to modulate the incident light. In this work we analyze the particular case where the FPI fringes are matched with very well defined rovibrational absorption lines of a target molecule such as CO(2), CO, N(2)O, or CH(4). In this kind of sensor, modulation is induced by scanning the FPI cavity length over one half of the reference wavelength. Here we present an analytical method based on the Fourier transform, which simplifies the procedure to determine the sensor response. Furthermore, this method provides a simple solution to finding the optimal FPI cavity length and mirror reflectivity. It is shown that FPI mirrors with surprisingly low reflectivity (<50%) are generally the optimum choice for target gases at atmospheric pressure. Finally, experimental measurements and simulation results are presented.     

Multilayer silicon cavity mirrors for the far-infrared p-Ge laser

Multilayer mirrors capable of > 99.9% reflectivity in the far infrared (70-200 microm wavelengths) were constructed using thin silicon etalons separated by empty gaps. Calculations indicate that only three periods are required to produce 99.9% reflectivity because of the large difference between the index of refraction of silicon (3.384) and the vacuum (1). The mirror was assembled from high-purity silicon wafers, with resistivity over 4000 omega cm to reduce free-carrier absorption. Wafers were double-side polished with faces parallel within 10 arc sec. The multilayer mirror was demonstrated as a cavity mirror for the far-infrared p-Ge laser. Dependence of reflectivity on design accuracy was considered.     

Highly dispersive mirror in Ta2O5/SiO2 for femtosecond lasers designed by inverse spectral theory

A highly dispersive mirror for dispersion compensation in femtosecond lasers is designed by inverse spectral theory. The design of a simple quarter-wave Bragg reflector can be modified by moving the poles in the optical impedance found in the photonic stop band. These spectral quantities are used as independent variables in the numerical optimization because they have no effect on the location of the photonic stop band, and so the design requirements to obtain a high reflectivity and a specific delay spectrum are decoupled. The design was fabricated by ion-beam sputtering. A group delay dispersion of -300 fs(2) was measured over a bandwidth of 28 nm, with a remaining reflectivity of greater than 99% in this range. The mirrors were used to make two Ti:sapphire lasers with 10- and 4-mm-long crystals, both of which generated near-transform-limited pulses of 35-fs duration. Because of the high dispersion of the mirrors, the laser cavities needed only five and three bounces from the mirrors, thus keeping reflection losses to a minimum.     

Development and Applications of Continuous-Wave Cavity Ring-Down Spectroscopy

Continuous-wave cavity ring-down spectroscopy (CW-CRDS) (using continuous-wave lasers) is now in widespread use for the sensitive detection of a range of different trace-gas species, including water vapor as a very important trace contaminant in many gases. It has also now been applied to monitor trace water vapor in a range of matrix gases, including those that are corrosive and have the potential for spectral interference with the target water-vapor species. The developments that have been carried out to achieve this will be discussed, and some of the applications, covering single sensors and multi-head sensors, will be presented. One limitation of the current sensor technology is that it uses mirrors that are highly reflective over a very restricted spectral range, and this limits a given sensor to the measurement of one or two gaseous species. Measurements of other species require the mirrors to be changed, as it is not currently practical to obtain mirrors with the required high reflectivity that also cover a large spectral range. The development of a new type of ring-down cavity that uses uncoated reflective optics, and which can be used from the ultraviolet to the infrared spectral regions, is presented. Examples of industrial and scientific applications are also presented.     

Effects of substrate and deposition method onto the mirror scattering

The effect of surface roughness onto the mirror scattering has been studied. Five kinds of substrates with different surface roughness were fabricated. On those substrates, dielectric multilayer coating for high reflectivity was deposited by ion-beam sputtering (IBS) and by electron-beam (EB) evaporation. Total integrated scattering (TIS) measurement setup was built for the evaluation of deposited samples. Most of the IBS mirrors showed lower scattering than the EB mirrors, which were deposited on the similar substrates in surface roughness. The ratio of substrate TIS to mirror TIS was defined for evaluation. It increased abruptly at approximately 2A in surface roughness, which indicated that to make low-loss mirrors, the substrate roughness should be less than 2A in rms.     

1D-photonic crystals prepared from the amorphous chalcogenide films

We describe the preparation and optical properties of the 15-layer chalcogenide dielectric mirrors with the first order stop bands in near infrared range. The high refractive index Sb–Se and low refractive index Ge–S layers were deposited on silicon and glass substrates using thermal evaporation method. To centre the stop bands of the prepared chalcogenide mirrors at 1.55 μm, the layer thicknesses, d(Sb–Se) = 117 and d(Ge–S) = 183 nm, were calculated from the quarter wave stack condition. The optical reflectivity measurements revealed the total reflection from the 15-layer chalcogenide mirrors in the range of 1,400–1,600 nm for the unpolarized light with normal incidence. The effect of annealing on the optical properties of the prepared chalcogenide mirrors was studied as well. Using spectral ellipsometry, we examined the angular dependence of the multilayers reflectivity for the light with s- and p-polarization. The preparation of the dielectric mirrors for near infrared region from chalcogenide films seems to be possible exploiting good optical quality of chalcogenide films and their simple deposition.     

Test station for optical elements exposed to high power synchrotron radiation beams

An experimental setup including a Michelson interferometer and an infrared camera for studying mirrors, crystals and other surfaces exposed to high power synchrotron radiation beams is described. Its performance is illustrated by first results for different test mirrors such as SiC, Cu, Al and monochromator crystals. A short, low-field wiggler in the DORIS II storage ring served as a light source with 25 W/mrad at a particle energy of 3.7 GeV for first tests.     

Analytical model for low finesse, external cavity, fiber Fabry-Perot interferometers including multiple reflections and angular misalignment

We present an analytical model for single mode, multiply reflected, external cavity, optical fiber Fabry-Perot interferometers in the low finesse regime using simple geometry and the Gaussian beam approximation. The multiple reflection model predicts attenuation of the peak-to-peak interference as the fiber to mirror distance approaches zero, as well as fringe asymmetry in the presence of nonabsorbing mirrors. A series of experiments are conducted in which a series of fiber Fabry-Perot cavities are constructed using uncoated, single mode glass fibers, and mirrors of varying reflectivity. The cavity length is swept, and the predictions of the model are found to be in good agreement with the experimental interferograms.