Abstract
Absorption spectra of the oxygen molecule A-band transition (ANNAJJ =P11Q10, v=392.3220 THz) are measured by current modulation of a DFB diode laser. We carry out measurements under two kinds of conditions. One is atmospheric open air in 298 K with an absorption length of 0.03 m at a repetition rates from 0.1 to 10 kHz, and the other is atmospheric air in 298 K in a cylinder of a Stirling engine which has a diameter of 0.02 m and length of 0.02 m at a repetition rate of 1 kHz. The scanned range of the light frequency is about 40GHz. We use a balanced detector and a 12-bit AD converter to reduce the noise level. The evaluated noise levels of the spectra are 1.7 x 10-5 at 10 kHz for the former case and 3.1 x 10-5 at 1 kHz for the latter case, and these values are about 2.5 and 4.4 times larger than the shot noise limit, respectively. We confirme that the shapes of the measured spectra are reproduced by calculation assuming a condition of 1 atm and 298 K.
