Cantilever-based photoacoustic detection of carbon dioxide using a fiber-amplified diode laser

A compact and sensitive photoacoustic setup has been developed based on a recently demonstrated cantilever technique. A micromechanical cantilever transducer is attached to a cylindrical photoacoustic cell and the cantilever’s deflection is monitored with a compact Michelson interferometer. A commercial 1-Watt optical fiber amplifier was used to enhance the performance of the system. A normalized sensitivity of 1.4×10^-10 cm^-1 W Hz^-1/2 was achieved in the detection of carbon dioxide at 1572 nm wavelength. Using 34 mW optical power from a DFB diode laser, the noise-equivalent detection limit for carbon dioxide at this wavelength is 4.0 ppm. Employing the fiber amplifier, we improved the sensitivity to yield measurement of sub-ppm concentrations. PACS 42.62.Fi; 42.55.Px; 82.80.Ch     

长光程共振式二氧化碳气体光声传感器研究

二氧化碳(CO₂)是植物光合作用的原材料,也是一种温室气体,其过量地排放会影响动植物的生态环境。在碳达峰、碳中和的背景下,研制高灵敏度的CO₂检测装置具有重要意义。为了监测大气环境中CO₂含量的变化,设计了一种长光程共振式CO₂气体光声传感器,并以此搭建了光声检测装置。以中心波长为2 004 nm的分布式反馈激光器(DFB)作为激发光源,激光射入由漫反射材料制成的球型吸收腔,在腔内多次反射以增加气体的吸收路径。吸收腔外部被两个高热传导率的铝制半球包裹,降低由池体吸收光能后产生的热噪声。吸收腔上耦合一根声学管,当其工作在一阶纵向共振模态时,光声信号被放大,在管子末端达到极大值。为了进一步增大光声信号,通过饱和加湿样品的方式来加快CO₂气体的弛豫速率,加湿后的样品产生的光声信号是干燥样品的2.1倍左右。使用一系列浓度的湿润CO₂样品标定光声检测装置,结果表明,光声信号与浓度之间呈现良好的线性关系。在此基础上,通过对标准气体的检测实验,验证了装置的准确性与稳定性...     

全光型石英增强光声光谱

设计并演示了一种全光型石英增强光声光谱技术, 该技术在传统的石英增强光声光谱系统中增加了另一束探测光束, 把与气体浓度成正比的石英晶振振臂的振动幅值转化为探测光束的强度变化, 实现了探测气体处无电子元件的全光学系统. 如此的设计使该系统具有较强的抗电磁干扰能力和非常小的传感头体积, 能够用于探测空间受限或探测环境恶劣的情况下, 并实现远距离探测. 在这种配置下, 探测大气压下的水汽, 获得的噪声等效吸收系数为1.13×10^-6 cm^-1W/√Hz. 进一步讨论了优化系统和提升其探测灵敏度的途径. 关键词： 石英增强光声光谱 音叉式石英晶振 气体传感     

Broadly tunable quantum cascade laser in cantilever-enhanced photoacoustic infrared spectroscopy of solids

An external cavity quantum cascade laser (EC-QCL) is applied in the photoacoustic detection of solid samples. The EC-QCL used has a broad tuning range of 676 cm^?1 (970–1,646 cm^?1) in the mid-infrared region, which enables accurate broadband spectroscopy of large molecules. The high spectral power density of the EC-QCL is combined with an extremely sensitive optical cantilever microphone of the photoacoustic detector to achieve an ultimate sensitivity. The carbon black, polyethylene, and hair fiber samples were measured with the EC-QCL photoacoustic detection using electrical amplitude modulation to demonstrate the possibilities of the setup. The same measurements were repeated with a Fourier transform infrared (FTIR) spectrometer combined with a photoacoustic detector for a comparison. The EC-QCL photoacoustic setup yielded roughly a decade better signal-to-noise ratios than the FTIR setup with the same measurement time.     

The GEO 600 core optics

The optical layout of the interferometric gravitational wave detector GEO600 is described in detail. Criteria for the choice of the geometry of this power- and signal recycled interferometer are presented, including the beam shape inside the interferometer and the surface figure of the optical components. Light power limits for the present setup are discussed. In addition, the demands for the mode cleaners and their performance are given.     

Single-element interferometer

A very simple and stable interferometer using a single optical element - a beam-splitter cube - is presented. The device resembles a two-arm interferometer in which the arms are together in one collimated beam, and the two beam halves interfere with the help of the beam-splitter cube. The proposed device produces simultaneously two interferograms with a relative phase-shift of π (rad). Since the period of straight interference fringes can be stably controlled, the device has potential application in spatial-carrier interferometry and for flexible writing of fiber Bragg gratings.     

高斯光束斜入射法布里-珀罗干涉腔后的反射光强分布

基于多光束干涉原理,推导了高斯光束斜入射法布里-珀罗干涉仪后的反射光强表达式.在此基础之上数值研究了入射角对高斯光束的反射特性的影响.研究结果表明:当法布里-珀罗干涉腔的腔长满足反共振时,随着入射角的增大,反射光的光强分散,峰值强度下降后呈现出幅度衰减的波动;峰值位置随着入射角的增大,呈现出幅度越来越小的振荡偏移;光斑大小随入射角的增大,呈现出幅度减小的振荡.     

Compact phase-shifted Sagnac interferometer for ultrasound detection

A compact fibre, phase-shifted Sagnac interferometer for ultrasound detection has been developed. The interferometer is a truly path-matched device, and therefore requires no path stabilization or heterodyning. It is a less expensive and more robust alternative to the heterodyne or path-stabilized Michelson interferometer. The device provides high spatial resolution of ultrasonic detection. It has been used in conjunction with conventional piezoelectric transducers (PZT) to detect Rayleigh and Lamb waves and to image a crack in a thin plate, rivet cracks in riveted plates, and for ultrasonic beam profiling.     

Generation of collinearly propagating orthogonally polarized beams

A simple monolithic device for simultaneous generation of collinearly propagating orthogonally polarized light beams of equal intensity is presented. The common cube beam splitter masked by two linear polarizers is used to achieve the purpose. This is experimentally verified through the use of a Stoke's polarimeter. It is also shown experimentally that the same setup behaves as a polarization phase shifting interferometer.     

Diffractive beam splitter characterization via a power-recycled interferometer

We used the high-precision laser interferometer technique of power recycling to characterize the optical loss of an all-reflective grating beam splitter. This beam splitter was used to set up a Michelson interferometer with a power-recycling resonator with a finesse of 883. Analyzing the results obtained, we determined the beam splitter's total optical loss to be (0.193+/-0.019)%. Low loss all-reflective beam splitters might find application in future high-power laser interferometers for the detection of gravitational waves.     

Noncontact photoacoustic imaging achieved by using a low-coherence interferometer as the acoustic detector

We report on a noncontact photoacoustic imaging (PAI) technique in which a low-coherence interferometer [(LCI), optical coherence tomography (OCT) hardware] is utilized as the acoustic detector. A synchronization approach is used to lock the LCI system at its highly sensitive region for photoacoustic detection. The technique is experimentally verified by the imaging of a scattering phantom embedded with hairs and the blood vessels within a mouse ear in vitro. The system's axial and lateral resolutions are evaluated at 60 and 30?μm, respectively. The experimental results indicate that PAI in a noncontact detection mode is possible with high resolution and high bandwidth. The proposed approach lends itself to a natural integration of PAI with OCT, rather than a combination of two separate and independent systems.     

Display of spatial coherence

The mutual-intensity function plays a major role in characterizing quasi-monochromatic, partially coherent optical signals. We demonstrate an optical system for displaying the mutual intensity of a one-dimensional input beam. The experimental system is based on the fact that the mutual intensity of a signal can be expressed as the ensemble averaging of a cross-correlation operation between two related optical signals. The setup consists of a Sagnac interferometer followed by an optoelectronic joint transform correlator. Experimental results demonstrate the capabilities of the mutual-intensity analyzer.     

A simple two-ray interferometer based on a beamsplitter cube

Results of analysis of a very simple, compact interferometer for recording holographic diffraction gratings, which allows continuous tuning of the angle between the interfering beams from 0° to 80°, are presented. The device consists of a single optical element, a beamsplitter cube. The lengths of arms in such an interferometer are automatically equal, and tuning is accomplished by changing the angle of incidence of the beam on the input face. Formulas for calculating the principal characteristics of the device are derived. It is shown that using a cube material with a higher index of refraction allows increasing the beam diameter and broadening the tuning range. Recommendations on the device design are provided.     

A modified moiré interferometer for three-dimensional displacement measurement

This paper presents a new optical interferometric system, MMI-T/G, composed of a modified four-beam moire interferometer and a Twyman/Green interferometer. The MMI-T/G system can measure threedimensional displacement fringe patterns with a single loading on the specimen, and the in-plane and out-of-plane displacement fields can be measured independently and defined clearly. The optical setup has the advantages of structural novelty, flexibility, and high fringe contrast. Moreover, the in-plane displacement sensitivity is twice of that of the normal moire interferometer. The measuring techniques to obtain the fringe patterns and displacement fields using the MMI-T/G system axe described. The experimental results of thermal displacement of an electronic device are shown.     

Angular interferometer using calcite prism and rotating analyzer

An interferometer using a calcite prism and rotating analyzer is proposed for angular displacement determinations. The calcite prism senses the angular displacements and the rotating analyzer transfers the interference signals from dc-type into ac-type. Compact optical setup and using low-cost devices are thus the advantages of the interferometer. The theory of the interferometer is first demonstrated. A setup constructed to realize the interferometer and the results of using this setup are then presented.     

Preliminary result of bunch length measurement using a modified Michelson interferometer

Based on the femtosecond accelerator device which was built at the Shanghai Institute of Applied Physics (SINAP), recently a modified far infrared Michelson interferometer has been developed to measure the length of electron bunches via the optical autocorrelation method.Compared with our former normal Michelson interferometer, we use a hollow retroreflector instead of a flat mirror as the reflective mirror.The experimental setup and results of the bunch length measurement will be described in this paper.     

Polarization phase-shifting Newton interferometer for plane optical surface measurements

This Letter introduces a polarization phase-shifting Newton interferometer that can be utilized for plane optical surface measurements, a setup constructed to realize the interferometer, and the experimental results from the use of the setup. The results confirm not only the validity but also the feasibility of the interferometer.     

Implementing the Deutsch's algorithm with spin-orbital angular momentum of photon without interferometer

Deutsch's algorithm is the simplest quantum algorithm which shows the acceleration of quantum computer. In this paper, we theoretically advance a scheme to implement quantum Deutsch's algorithm in spin-orbital angular momentum space. Our scheme exploits a newly developed optical device called "q-plate", which can couple and manipulate the spin-orbital angular momentum simultaneously. This experimental setup is of high stability and efficiency theoretically for there is no interferometer in it.     

Ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer using a beam collimator and its application for ultrasonic imaging of seismic physical models

An ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer(FPI) is proposed and employed for ultrasonic imaging of seismic physical models(SPMs). The FPI comprises a flexible ultra-thin gold film and the end face of a graded-index multimode fiber(MMF), both of which are enclosed in a ceramic tube. The MMF in a specified length can collimate the diverged light beam and compensate for the light loss inside the air cavity, leading to an increased spectral fringe visibility and thus a steeper spectral slope. By using the spectral sideband filtering technique, the collimated FPI shows an improved ultrasonic response. Moreover, two-dimensional images of two SPMs are achieved in air by reconstructing the pulse-echo signals through using the time-of-flight approach. The proposed sensor with easy fabrication and compact size can be a good candidate for high-sensitivity and high-precision nondestructive testing of SPMs.     

利用Michlshon干涉仪测量CCD的调制传递函数

介绍了利用Michlshon干涉仪测量CCD调制传递函数的方法,与其他方法相比,该方法具有测量装置简单、将正弦图样投射到待测CCD阵列上无需借助光学系统等特点。给出了典型的线阵和面阵CCD的调制传递函数曲线的测量结果。