摘要
将波长调制光声光谱和光热光谱有效结合,提出了一种基于石英音叉探测器和光声光谱与光热光谱技术有效融合的双光谱气体检测技术。以大气中水汽为分析对象,利用1 392 nm附近的近红外半导体激光器搭建了一套基于石英音叉探测器的双光谱探测系统,结合波长调制技术中相位依赖特性,利用差分原理实现了波长调制光声光谱和光热光谱信号的有效叠加和增强,与传统探测方案中采用的单一光谱检测方法相比,有效利用了激光功率,实验结果显示,所提出的双光谱探测技术的总体信噪比分别是光声光谱与光热光谱信噪比的1.97和1.24倍,有效提升了系统检测灵敏度。
Laser spectroscopy is a powerful analytical technique based on the interaction process of light and matter (including absorption,reflection,scattering,refraction,interference,etc.),which can provide various useful information (such as composition,concentration,velocity,flux,etc.) by analyzing the detected spectral signal and combing the related physical principles.With the continuous innovation of modern laser light sources and photodetector devices,the laser spectroscopy technique has also been developed rapidly.In terms of the three core components of the laser spectroscopy system (i.e.,laser light source,absorption cell,and photodetector) and signal enhancement and noise suppression methods,various advanced laser spectroscopy techniques or detection methods have been developed.Quartzenhanced photoacoustic spectroscopy and photothermal spectroscopy is a new and rapidly developing laser spectroscopy technique,which utilizes miniaturized quartz tuning forks as detectors with the advantages of small size,high quality factor,and low cost.Quartz-enhanced photoacoustic spectroscopy is a spectroscopic technique that measuring the aco of light and gas in a radiation-free relaxation process,which utilizes the resonance effect and piezoelectric effect of the quartz tuning fork as an acoustic detector.However,the quartz-enhanced photothermal spectroscopy technique is based on the thermoelastic effect using quartz tuning fork as a light detector.To date,quartz-based enhanced photoacoustic and photothermal spectroscopy have been successfully applied to detect many small molecules with narrow absorption spectra and several large molecules with broad,unresolved spectral absorption features.These two techniques have been widely used for developing real-time and compact trace gas sensors with high sensitivity and selectivity.In this paper,a dual-spectroscopy detection technique based on quartz tuning forks is proposed to further improve the sensitivity of the quartz tuning fork based spectroscopic detection technique.To demonstrate this proposed gas detection technique,atmospheric water vapor (H2O) was used for the analytic target and a dual-spectroscopy gas detection system based on two quartz tuning fork detectors (i.e.(QCTF1 and QCTF2) is developed by combing a near-infrared (NIR) diode laser emitting near 1 392 nm,the laser beam is directly coupled into an optical fiber collimator and allowing pass between the two vibrating arms of the QCTF1 detector,which is used to detect the photoacoustic signal generated from the absorption process of atmospheric water vapor.The laser beam between the two arms of the QCTF1 is then focused on the surface of the side arm of the QCTF2 detector through a CaF2lens,which is used to detect the photothermal signal generated in the same environmental conditions.Moreover,the wavelength tuning characteristics of the laser were measured before the experiments,and the dependence of the emission wavelength on the driving voltage of the DFB laser at a temperature of 34℃was obtained to ensure that the laser emission wavelength could effectively cover the absorption line of H2O near the optical wavelength of 1 391.67 nm.Since other gas molecules in ambient air,such as CH4,CO,O2and CO2have not obvious absorption features near 1 391.67 nm,therefore,the spectral interference from other molecules can be effectively avoided.The resonance profile curve and the signal amplitude of the quartz tuning fork detectors are precisely measured as a function of the excitation position,and the optimal modulation frequency and excitation position are also experimentally determined,which is of great significance to improve the detection sensitivity of the proposed dual-spectroscopy detection technique.To further improving the sensitivity,the wavelength modulation technique is combined with the phase-dependent characteristics,and the effective signal enhancement of the wavelength modulated photoacoustic and photothermal spectral signals are realized by using the difference detection principle,which effectively utilizes the laser power compared with the single spectraldetection method used in the traditional detection scheme.The experimental results show that the overall Signal-to-Noise ratio (SNR) of the proposed dualspectroscopy detection technique is 1.97 and 1.24 times higher than those of photoacoustic and photothermal spectral signal,respectively,which effectively improves the system detection sensitivity.Finally,the relationship between the photoelectric conversion efficiency of the quartz tuning fork and the incident laser power in the dual-spectroscopy detection technique is investigated.The experimental results show that the quartz tuning fork detector has a good linear response to the incident laser power with a regression coefficient R~2=0.996,which indicates the sensitivity can further improved by using laser sources with more high output power.
作者
王强
王浩
肖聪
李劲松
WANG Qiang;WANG Hao;XIAO Cong;LI Jinsong(School of Physics and Optoelectronic Engineering,Anhui University,Hefei 230601,China)
出处
《光子学报》
EI
CAS
CSCD
北大核心
2023年第3期220-228,共9页
Acta Photonica Sinica
基金
国家自然科学基金(Nos.41875158,61675005)。
关键词
光声光谱
光热光谱
石英音叉探测器
双光谱技术
气体探测
Photoacoustic spectroscopy
Photothermal spectroscopy
Quartz tuning fork detector
Dual spectroscopy techniqe
Gas detection
