All Optical Quartz-enhanced Photoacoustic Spectroscopy

Quartz enhanced photoacoustic spectroscopy (QEPAS) technology is a new type of photoacoustic spectroscopy in recent years. The photoacoustic detection module which due to the small size, high sensitivity, low cost, strong anti-interference is widely used in the field of trace gas detection for environmental monitoring, industrial process control, medical diagnostics. With the development of science and technology, traditional QEPAS technology needs to be improved in order to adapt to innovations in the field of special requirements related trace gas detection device. In addition, since the conventional QEPAS technique uses the piezoelectric effect produce a weak electrical signal proportional to the measured gas concentration, thus making it vulnerable to detection by electromagnetic interference environment, and can’t achieve long-range detection. To solve these problems, we propose a model of all-optical quartz enhanced photoacoustic spectroscopy technique,which is the use of the principle of detecting the reflected beam quartz tuning fork vibration signal, the vibration amplitude is proportional to the gas concentration of quartz tuning fork rallying conversion to detect changes in the intensity of the beam, the ultimate goal of obtaining relevant information to detect gas.This paper introduces the traditional photoacoustic spectroscopy; then describe the characteristics of quartz and quartz tuning fork enhanced photoacoustic spectroscopy technology works, and describes two popular configurations of quartz enhanced photoacoustic spectroscopy:the on-beam and off-beam QEPAS. Also reported on the current quartz enhanced photoacoustic spectroscopy system, the latest variant of the research, pointed out the problems and disadvantages of these systems when used in special applications.Deal with the problems, we first proposed all-optical quartz enhanced photoacoustic spectroscopy and analysis system based on a scientific theory to design and build a trace gas sensing system based on the technology. The water vapor in the air as the probe gas, measured by the experimental analysis of the scientific assessment of the performance of the device. The results show that its normalized noise equivalent absorption coefficient of 1.13×10-6cm-1WHz-1/2, it contrast with the traditional quartz enhanced photoacoustic spectroscopy is fairly.To further improve the performance of the device, we propose an improved optimization program which will be combined with the Michelson interferometer type of sensitive to small displacement, and to improve the overall system’s sensitivity by increasing the detection small displacement measurement of tuning fork. By optimizing the optical system design, to obtain a clear interference pattern and to detect significant changes in the interference fringes. Water vapor in the air as a tracer gas, get the noise equivalent normalized coefficient of 4.005×10-8cm-1WHz-1/2. This novel device design not only has a strong anti-electromagnetic interference performance also has the ability to make long-range detection. The all-optical system can be used for high temperature, high humidity, explosive detection, and detection of space-constrained environments trace gases, which greatly expand the applications of technology-based QEPAS trace gas detection device.