Design Of Trace Gas Detection System Based On The Quantum Cascade Lasers

A wide variety of gas plays a very important role in industrial and agriculturalproduction, but also is related to human health and life safety. Therefore, modernmeasurement method in the gas quantitative analysis technology is more and more drawpeople’s attention. Photoacoustic spectroscopy technique, featured as high detectionsensitivity, good selectivity and fast response characteristics, is the ideal way to realizegas analysis and real-time monitoring. The latest research progress of semiconductorLaser and laser light source driver has reached new heights, which lays foundation forthe trace gas analysis from the laboratory research to commerce.This paper constructs a practical miniaturization trace gas detection system byusing quantum cascade laser pulse as excitation source of the PA cavity, which makes afull theoretical preparation for next physical implementation of the system.Through the theoretical analysis, we design a driving of the quantum cascade lasers,based on its characteristics, power supply adapted to the working conditions. The drivepower is composed of three parts: pulse drive current control and temperature control,work status display. The pulse current drive is designed by using negative feedback ofthe current pulse for real-time monitoring to the current flowing through the laser.As for realization of the temperature control part, thermistor resistance changeswith the variation of the laser operating temperature, the current of chilling plate iscontrolled through comparation between the sampling voltage and default voltage valueto achieve automatic controlling of temperature. Meanwhile, based on the basic theoryof the gas photoacoustic effect, the photoacoustic signal generation mechanism isanalyzed. Then, the <100> mode cylindrical cavity photoacoustic signal generationprinciple and transform from the time domain to the frequency domain of photoacousticsignal are discussed deeply. The core issues about photoacoustic cavity design andmicrophone matching system design based on quantum cascade laser light source arediscussed in detail.By the virtual instrument technology from the LabView software platform, andbased on PC sound card, a signal detection system comes into being, which reduce the difficulty of the design of the system from the premise of the resolution of the system.