摘要
使用中心波长为450 nm的高功率多模蓝光激光管(LD)作为激励光源,结合电学调制相消法和离轴石英增强光声光谱(QEPAS)配置,设计了一款高灵敏二氧化氮传感器.电学调制相消法使离轴QEPAS传感器的背景噪声降低至1/269,在标准大气压和1 s积分时间下,获得的探测灵敏度为4.5 ppb,对应的归一化噪声等效吸收系数(1σ)为2.2×10-8cm-1·W/Hz1/2.延长积分时间到46 s,灵敏度能够进一步下降到0.34 ppb.气体流速对该传感器的影响也被研究.
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
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第13期48-54,共7页
Acta Physica Sinica
基金
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)
山西省高等学校创新人才支持计划资助的课题~~
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
electric modulation cancellation method
quartz enhanced photoacoustic spectroscopy
off-beam quartz ehnhanced photoacoustic spectroscopy sensor
high power laser diode
