Water vapor absorption spectrum measurements and its application in concentration measurement

Wavelength tunable distributed feedback laser diode (DFB-LD) were utilized to measure line 1368.597nm and line 1367.862 nm absorption character of water vapor, based on it, water vapor concentration can be measured by peak absorption rate according to Beer-Lambert law. Besides, we observe that the overlap between the line 1368.597nm and line 1367.862 nm appears and become serious with the increase of gas pressure, this agrees well with the theoretical prediction, and the overlap cause difficulty to determine the absorption peak value, a scheme is presented to cope with the difficulty, it takes advantage of the peak absorption difference between 1368.597nm and 1367.862 nm, and the difference value is used to calculate the water-vapor concentration.