高灵敏度便携式激光仪

达泰克（B&WTEK Inc.）和柯尼卡美能达公司（Konica Minolta Sensing Americas）合作推出新一代低成本、高分辨率和高灵敏度的SpectraRad辐照度光谱仪。SpectraRad是采用了TE致冷CCD光谱仪和独有透射式余弦校正部件的辐照度光谱仪系统，系统经NIST溯源的标准灯进行照度校正，采用USB2.0/1.1数据传输，配备BWSpec专用光源检测软件，提供CIE1931标准中的光学检测指标，是LED、照明光源及各类太阳能模拟器等特殊光源检测的理想选择。 更多有关SpectraRad的信息，请访问http://www.bwtek.cn/product.asp?ID=59&SortID=5或http://www.bwtek.com/product/colormeasurement/spectrarad.html 美国必达泰克公司（B&W TEK）是一家主营光电产品的高科技公司，成立于1997年，位于美国特拉华(Delaware)州纽瓦克(Newark)市。本公司集开发、研制、生产于一体，在CCD、PDA、InGaAs等阵列光谱仪以及拉曼、荧光等光谱系统、高功率半导体激光器等方面均处于世界领先水平，其中便携式拉曼光谱仪全球销量超过8000台。 必达泰克在分子光谱仪器特别是近红外、拉曼光谱仪等中高端领域拥有强大的技术实力，仪器各项指标先进，售后及技术服务完善，在广大客户群中拥有优秀的声誉。必达泰克公司的各型CCD/PDA微型光谱仪、便携式拉曼光谱仪以及激光共聚焦显微拉曼光谱仪广泛应用到LED测试、制备色谱、在线污染气体检测、水质分析、宝玉石文物鉴定等多个领域。值得一提的是，必达泰克公司（B&W TEK）率先在中国市场推出高灵敏度非致冷薄型背照式CCD阵列光谱仪等多款高性价比产品。作为必达泰克公司在中国的全资子公司，必达泰克光电科技致力于为中国客户提供一流的仪器，一流的服务。

近日，来自安徽科技理工大学、安徽西部大学皖西学院、复旦大学大气与海洋科学学院、上海期智研究院的联合研究团队发表了《通过实施光学条纹噪声抑制方法的激光波长调制光谱技术实现气体测量的高精度和高灵敏度检测》论文。Recently, the joint research team from Anhui University of Science and Technology, West Anhui University, Department of Atmospheric and Oceanic Sciences, Fudan University, Shanghai QiZhi Institute published an academic papers High precision and sensitivity detection of gas measurement by laser wavelength modulation spectroscopy implementing an optical fringe noise suppression method.可调谐二极管激光吸收光谱（TDLAS）已被开发用于痕量气体测量，因其高精度、高灵敏度和无需任何样品准备的原位自校准的独特优势。通常，长光程的多次通过腔体（MPC）被应用于增强基于TDLAS的传感器的检测精度和灵敏度。然而，MPC中出现的意外光学干涉纹严重影响了传感器的检测精度和灵敏度。基于MPC的TDLAS传感器的检测精度和灵敏度通常受到光学干涉纹的限制，这些干涉纹由衍射、镜面表面瑕疵的散射、镜面畸变、热膨胀、冷收缩或应力变形引起。因此，MPC中观察到的光学干涉纹由不同的光学干涉纹组成。这些光学干涉纹主要是由于少量的激光以与主激光束相差ΔL的光程到达探测器所致。这些问题对于TDLAS是普遍存在的，尤其是在使用密集重叠斑点模式的MPC时，提出了一些不同的方法来消除光学干涉纹的负面影响。The Tunable Diode Laser Absorption Spectroscopy (TDLAS) has been developed for trace gas measurement, as its unique advantages of high precision, high sensitivity and self-calibration in situ qualification with-out any sample preparation. The multi-pass cell (MPC) with a long optical path is usually applied to enhance TDLAS-based sensor’s detection precision and sensitivity. However, the unexpected optical fringes occurring in the MPC often spoil the sensor’s detection precision and sensitivity seriously. The detection precision and sensitivity of the TDLAS-based sensors containing an MPC are often limited by the optical fringes that result from diffraction, scattering on the mirror surface imperfections, mirror aberration, thermal expansion, cold contraction, or stress deformation. Therefore, the complex optical fringe consisting of different optical fringe will be observed in the MPC. These optical fringes are due largely to a small amount of laser reaching the detector with an optical path length differing by ΔL from the main laser beam. Those problems are common for TDLAS, especially using dense overlapped spot pattern MPC and some di&fflig erent methods are proposed to eliminate the negative influence of the optical fringes.研究团队提出了一种抑制可调二极管激光吸收光谱中光学条纹噪声的新方法，并将其应用于由光学条纹扰动的CH4气体传感器，以提高检测精度和灵敏度。所开发的CH4检测仪的示意图如图1所示。宁波海尔欣光电科技有限公司为此项目提供锁相放大器（HPLIA 微型双通道调制解调锁相放大器），从光电探测器输出的信号发送到锁相放大器，锁相放大器相对于同步信号对2f模式进行解调，锁相放大器的时间常数设为1ms。In this work, a novel method to suppress optical fringe noise in the tunable diode laser absorption spectroscopy is proposed and applied to the CH4 gas sensor perturbed by optical fringes for higher detection precision and sensitivity.The schematic diagram of the developed CH4 detection instrument is shown in Fig. 1 . HealthyPhoton Co.,Ltd provided a HPLIA Miniature dual-channel modulated demodulation lock-in amplifier for this project. The lock-in amplifier demodulates the signal in the 2f mode with respect to the sync signal. The time constant of the lock-in amplifier is set to 1 ms.Fig.1. Schematic diagram of the developed CH 4 detection systemlock-in amplifier (Healthy Photon, HPLIA)对于被光学条纹和随机噪声干扰的20 ppm CH4的二次谐波(2 f)信号，通过该新方法，2f信号的信噪比(SNR)从17提高到182，优化平均光谱范围Δ𝜆 。与未经处理的原始信号相比，CH4测量精度改善了约1.5倍。相应的最小可检测浓度可从3 ppb改善到0.78 ppb。系统的相应噪声当量吸收灵敏度(NNEA)和噪声当量浓度(NEC)分别为6.13 ×10-11 cm&minus 1 W Hz&minus 1/2 and 0.181 ppm。For the 2nd harmonic(2f) signal of 20 ppm CH4 spoiled by optical fringes and random noise, by the novel method, the signal-to-noise ratio (SNR) of the 2f signal is improved about 6.5 times from 17 to 182 with an optimal averaging spectral range Δ𝜆 . A &sim 1.5 times improvement in the measurement precision of CH4 is achieved compared to unprocessed raw signal. The corresponding minimum detectable concentration can be improved from 3 ppb down to 0.78 ppb. The corresponding noise equivalent absorption sensitivity (NNEA) and the noise equivalent concentration (NEC) of the system is 6.13 ×10-11cmW-1Hz-1/2 and 0.181 ppm, respectively.Violet line from traditional averaging method and magenta line from the novel optical fringe noisesuppression method.Histogram plot of the 20 ppm CH 4 deviation.20 ppm CH 4 Allan-deviation stability of developed overlapped spot pattern MPC.参考文献：Reference:Yanan Cao, Xin Cheng, Zong Xu, Xing Tian, Gang Cheng, Feiyan Peng, Jingjing WangHigh precision and sensitivity detection of gas measurement by laser wavelengthmodulation spectroscopy implementing an optical fringe noise suppression method, Optics and Lasers in Engineering 166 (2023) 107570www.elsevier.com/locate/optlaseng

近期，中国科学院合肥物质科学研究院安徽光学精密机械研究所大气物理化学二室的刘锟等研究人员在高灵敏度小型化吸收光谱传感技术研究中取得了新的进展。研究成果发表在Sensors & Actuators: B. Chemical(220, 1000-1005)上。　　基于吸收光谱的光学传感技术，因其实时在线、高灵敏度、高选择性和非入侵式等优点，被广泛应用于大气、环境和工业等领域。为了提高吸收光谱传感的灵敏度，往往通过光学多通吸收池增加光和样品的相互作用程长。然而，受光斑重合等因素的限制，传统的光学吸收池(如Herriott池)很难实现上百次的光反射，长光程只能靠增加物理池长度的方式得到，这样大大增加了吸收池的体积，难于实现小型、便携的高灵敏度传感设备。　　刘锟等研究人员通过精心的设计，在普通球面反射镜上实现反射光斑呈7个圆圈的分布，充分利用了反射镜的反射面，在光斑不重合的情况下实现了高达215次的光反射，从而用12cm物理基长实现了26米的有效光程。刘锟等研究人员利用所设计的新型光学吸收池，开展了大气甲烷(CH4)的测量研究，实现了100ppb(10-9)的探测灵敏度和优于80 ppb的测量精度。这一研究成果为发展小型化、便携式高灵敏度光学传感器提供了有效的手段，也将推动对体积、重量要求严格的无人机大气探测技术等应用的发展。　　该研究工作受到国家自然科学基金、中国科学院青年促进会等经费资助。