7.4um QCL combined with 5-meter long optical path miniaturized Mini hollow fiber gas chamber gas analysis system for analyzing H2O in air

Theoretical basis 1. Bill Lambert law: When a laser passes through a gas with a concentration of C, when the wavelength of the laser is the same as the center frequency of a certain absorption spectrum line of the gas, gas molecules will absorb photons and transition to high energy levels, manifested as the attenuation of laser intensity in the gas absorption band. 2. Wavelength modulation spectroscopy technology. A) Tuning characteristics of lasers. DFB lasers, due to their good monochromaticity, narrow linewidth, and frequency tuning characteristics, can effectively avoid cross interference from other background gases, making the detection system have good measurement accuracy. Therefore, they are widely used in gas detection. B) Harmonic detection theory changes the current by adding a high-frequency sine voltage signal to the driving voltage of the laser, so that the output frequency also follows a sine waveform. Regular changes. By applying sawtooth voltage to the laser driver, the output wavelength is scanned on both sides of the gas absorption peak. The harmonic signal is modulated and demodulated using a lock-in amplifier to measure gas concentration. 3. The principle of selecting absorption spectral lines is crucial in gas detection, and the following aspects should be considered: (1) the selected spectral lines of the gas.........