Quartz Photoacoustic Spectral Sensing System Based on Parallel Incidence

Abstract

The invention discloses a quartz photoacoustic spectrum sensing system based on parallel incidence. The sensing system includes a semiconductor laser, an optical collimator, a quartz tuning fork, a data acquisition system and a computer arranged in sequence along the beam propagation direction. The present invention designs a new way for the laser to be incident on the quartz tuning fork. The laser is incident parallel to the strands of the quartz tuning fork, passes through the middle of the strands of the tuning fork, and finally hits the bottom of the tuning fork directly. Since the length of the quartz tuning fork is much greater than its thickness, the effective interaction distance between the laser and the gas will be greatly increased, thereby improving the effect of sound waves on the quartz tuning fork, increasing the output signal of the quartz tuning fork, and ultimately improving the sensitivity of gas detection.

Description

technical field [0001] The invention relates to a quartz photoacoustic spectrum sensing system. Background technique [0002] Quartz-enhanced photoacoustic spectroscopy is an indirect absorption spectroscopy technique that uses a quartz tuning fork as a detection element. The basic principle of quartz-enhanced photoacoustic spectroscopy is the photoacoustic effect. The so-called photoacoustic effect means that the absorbing gas absorbs light energy and converts it into heat energy through a non-radiative transition form, which will lead to an increase in the local temperature of the absorbing gas and a change in pressure. If the light energy is periodically modulated, the local temperature increase and pressure change will also be periodic. If the modulation frequency is at the audio frequency, then sound waves will be generated. When the sound source is located in the middle of the two fork strands of the quartz tuning fork, the pressure wave will produce opposite forces ...

AI Technical Summary

Problems solved by technology

Since the tuning fork strands can only produce effective signals when they swing in opposite directions, the laser incident needs to pass between the two tuning fork strands. At present, the laser incidence method is to pass through the tuning fork strands vertically ( figure 1 As shown), the method is relatively simple. The gas interaction between the laser and the tuning fork strands generates an acoustic signal, which is converted into a current signal output through the piezoelectric effect of the quartz crystal, and the concentration of the gas to be measured is obtained by inverting the output current signal through demodulation.

[0003] In the existing laser incident mode, the effective distance between the laser and the gas is short, only the thickness of the tuning fork is about 0.36 mm ( figure 1 ), resulting in the weak effect of the sound wave generated by the photoacoustic effect on the quartz tuning fork, which in turn makes the output current signal of the tuning fork smaller (about pA level), and finally affects the sensitivity of gas detection

In addition, in this scheme, the relative distance between the laser and the top of the tuning fork will also affect the output signal strength, which makes the system adjustment very complicated and requires high system stability

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