TDLAS (Tunable Diode Laser Absorption Spectroscopy) It uses the laser wavelength modulation to pass through the characteristic absorption region of the measured gas Diode laser And Long optical path absorption cell Based on t...
TDLAS (Tunable Diode Laser Absorption Spectroscopy) It uses the laser wavelength modulation to pass through the characteristic absorption region of the measured gas Diode laser And Long optical path absorption cell Based on the combination, a new gas detection method has been developed. TDLAS technology Semiconductor laser source The width of the spectrum of TDLAS is far less than the broadening of the gas absorption spectrum, and the single line absorption spectrum is obtained. Therefore, TDLAS technology is a high-resolution absorption spectrum technology.

This week, we used space light interpenetrating technology to detect the absorption peak of water molecules in the air, so as to detect the presence of water in the air. The absorption peak of water is near 1392nm, and we chose a 1392nm DFB laser, The LD temperature is controlled to 30 ℃, and the current is controlled to 25mA. The output laser is converted into spatial light collimation output with a large aperture collimator.

The collimating performance of the large aperture collimating head is very good, and the radius of the light spot is almost unchanged within a few meters. A large aperture collimating head is also placed 2 meters away to collect the transmitted 1392 nm space light and couple it into 1550 nm Single mode fiber Optical fiber transmission.

stay Fiber patch cord End, connect a PD Photodetector Conduct photoelectric conversion, and finally send the electrical signal through the cable Phase-locked amplifier 。 The device diagram is as follows:

The voltage signal output by the phase-locked amplifier is connected to the drive module of the laser to modulate the laser frequency. We have selected a superposition signal of 4Hz sine wave and 22kHz sine wave as the output signal. The 4Hz voltage signal has a large amplitude of ± 350mV, which is used to scan the laser frequency to ensure that it can sweep the absorption peak of water. The 22kHz sine wave is used to modulate the laser frequency with a small amplitude, mainly to avoid the environmental noise at low frequencies, And use demodulation technology to reproduce the absorption signal of water. The figure below shows the configuration information of the phase-locked amplifier in this experiment, and it has a built-in oscilloscope that can directly display the demodulated waveform. The figure shows the absorption peak of water molecules at 1392nm.
