Measurement of H2O concentration by tunalbe laser absorption spectroscopy technique with a Tm:YAP solid-state laser

This work investigates a tunable laser absorption spectroscopy technique for the H2O concentration by a Tm:YAP solid-state laser. The output wavelength of Tm:YAP laser is tuned by a birefringence filter and an F-P etalon in the laser cavity. The tuning range is from 1910 nm to 1914 nm, the tuning frequency is 1 Hz. With the tunable Tm:YAP laser, we realize a concentration resolution of 10 ppb. Different concentrations of H2O vapor are use to test the precision of the system. A maximum relative error of 0.8% is realized. At the same time, we calculate the maximum absolute error to be 0.8 ppm. Up to the authors' knowledge, it is the first time to report a tunable laser absorption spectroscopy for the gas concentration measurement by a Tm-doped laser.