Laser heterodyne radiometers using a CO_2 laser and a Pb-sault diode laser as local oscillators have been developed for detecting stratospheric minor constituents such as ozone and sulfur-bearing conpunds. Because of very low concentration of the latter gases in the stratosphere, it is required that the radiometer has the near quantum limited sensitivity and is capable of operation at the stratospheric altitude for limb-scanning of the atmosphere to the sun. Considering this requirement, we obtained the best design of the beam combining optics between signal and local laser beams, so that the measured system sensitivities of our CO_2 laser and diode laser heterodyne radiometers have attained to be as high as NEP/B=1.7×10^<-19>W/Hz and 5.9×10^<-19>W/Hz, which are only 8.1 and 29 times the quantum noise lovel, respectively. A number of absorption lines including stratospheric ozone lines have been successfully measured by a groundbased observation of the solar radiation at 9.6μm wavelength. An airborne laser heterodyne radiometer using the same technique will be developed in future.
大気微量成分測定用赤外レーザヘテロダイン分光計の開発
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