Measurement of the Hot Zone Temperature Using 1f  Modulation Diode Laser Absorption Spectroscopy with Logarithmic Signal Conversion

New version of diode laser (DL) absorption spectroscopy (DLAS) for determining the hot zone temperature is developed. The method is based on the combination of slow scanning of the radiation frequency of a probe DL around the absorption line of a test molecule of the medium and fast radiation frequency modulation with an amplitude on the order of the absorption line width. The developed version of the wavelength-modulation (WM-DLAS) is based on the two-beam differential scheme, the logarithmic signal conversion, and the registration of absorption at the first harmonic of the modulation frequency. The two-beam differential registration scheme and the logarithmic conversion of absorption signals have made it possible to reduce substantially the nonselective absorption of probe radiation and registration noise determined by excessive noise of lasers. The application of the first harmonic has ensured a higher sensitivity of the proposed version of WM-DLAS. Using the technique developed in this study, we have measured the temperature of water vapor in atmospheric air in the range 700–1100 K. The results are compared with the data obtained using commercial thermocouples. The difference in temperatures measured by a standard thermocouple and its mean value determined using the technique developed here is 40 K for a temperature of 1000 K and 30 K for 800 K.