DETERMINATION OF ABSORPTION LINE PARAMETERS USING TWO-TONE FREQUENCY-MODULATION SPECTROSCOPY WITH DIODE LASERS

Abstract Accurate determination of line parameters from weak absorption using two-tone frequency-modulation spectroscopy (TTFMS) with a GaAlAs diode laser is demonstrated. The air-broadening of three oxygen A-band lines is determined, using a least-squares fit. For a peak absorption of 1.3 × 10 -3 the deviation between the experimental and the fitted spectrum is less than 1%. The fitting procedure is successfully tested on absorptions as small as 4.5 × 10 -5