Linewidths only limited by the transit time and by collisions are obtained in stimulated Raman and Rayleigh spectroscopy by a second-harmonic detection in high-frequency modulation transfer. The distortion of the line shape due to a residual amplitude modulation is shown to vanish for a third- or a fourth-harmonic detection with a proper choice of the modulation index and the detection phase.
['F. du Burck', 'Jean-Pierre Wallerand', 'A. N. Goncharov', 'M. Himbert']
High-frequency modulation transfer technique for ultra-high resolution spectroscopy of I/sub 2/