基于电学调制相消法和高功率蓝光LD的离轴石英增强光声光谱NO2传感器设计和优化∗
Design and optimization of off-b eam NO2 QEPAS sensor by use of E-MOCAM with a high p ower blue laser dio de
摘要
Abstract
A highly sensitive NO2 optical sensor has been designed by means of combining the electrical modulation cancellation method (E-MOCAM) and off-beam quartz enhanced photoacoustic spectroscopy (QEPAS). A high power multimode blue laser diode emitting at around 450 nm is used as the excitation light source of the photoacoustic signal. In the E-MOCAM, the balance signal is generated from a dual-channel function generator and introduced to the pin of the quartz tuning fork (QTF) to balance out the huge background noise. The principle of the E-MOCAM is explained in detail from the perspective of equivalent circuit of QTF, and the background noise of the high power LD-based QEPAS sensor is analyzed. Results show that stray light noises coming from the LD beam and blocked by the resonator and the photoacoustic cell are dominated in all the noises. Gas flow noise of QEPAS sensor is also estimated, and excessive noise could be introduced by the gas flow even at a rate below 200 sccm. The gas flow noise is measured at different gas flow rate, from 60 to 200 sccm. Compared with the QEPAS sensor based on wavelength modulation, the sensor based on amplitude modulation, especially in the case of high power light source, is more sensitive to the gas flow. The ultimate background noise of the off-beam QEPAS sensor can be reduced by 269 times after the E-MOCAM is applied. The performance of the NO2 QEPAS sensor is evaluated in the NO2/N2 mixtures of different concentrations, ranging from ppb to ppm levels. In the case of the 2.85 ppm NO2 measurement, the SNR of 630 is achieved. A linear fitting is implemented to evaluate the response of the sensor, resulting in an R square value of 0.999. Allan plot is used to investigate the long term stability of the sensor. The original background noise produced from the off-beam QEPAS configuration is less than that from the on-beam QEPAS configuration, thus the combination of off-beam QEPAS configuration and E-MOCAM shows a better stability. A detection limit of 0.34 ppb (1σ, 46 s integration time) for NO2 in N2 at atmospheric pressure can be achieved, which corresponds to a normalized noise equivalent absorption coefficient of 2.2 × 10−8 cm−1·W/Hz1/2 .关键词
电学调制相消法/石英增强光声光谱/离轴石英增强光声光谱传感器/高功率激光管Key words
electric modulation cancellation method/quartz enhanced photoacoustic spectroscopy/off-beam quartz ehnhanced photoacoustic spectroscopy sensor/high power laser diode引用本文复制引用
尹旭坤,郑华丹,董磊,武红鹏,刘小利,马维光,张雷,尹王保,贾锁堂..基于电学调制相消法和高功率蓝光LD的离轴石英增强光声光谱NO2传感器设计和优化∗[J].物理学报,2015,(13):1-8,8.基金项目
国家自然科学基金(批准号:61275213,61108030,61127017,61178009,61378047,61475093,61205216)、国家重点基础研究发展计划(973计划)(批准号:2012CB921603)、国家科技支撑计划(批准号:2013BAC14B01)、山西省青年科学基金(批准号:2013021004-1,2012021022-1)、山西省回国留学人员科研资助项目(批准号:2013-011)、山西省留学回国人员科技活动资金(批准号:2013-01)和山西省高等学校创新人才支持计划资助的课题.* Project supported by the National Natural Science Foundation of China (Grant Nos.61275213,61108030,61127017,61178009,61378047,61475093,61205216), the Basic Research Program of China (Grant No.2012CB921603), the National Key Technology R&D Program (Grant No.2013BAC14B01), the Shanxi Natural Science Foundation, China (Grant Nos.2013021004-1,2012021022-1), the Shanxi Scholarship Council of China (Grant Nos.2013-011,2013-01), and the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi （批准号:61275213,61108030,61127017,61178009,61378047,61475093,61205216）
