The effect of the laser-atom interaction time on the influence of velocity-changing collisions in Doppler-free spectroscopy

Remarkable reduction of the influence of velocity-changing collisions in Doppler-free optogalvanic spectra has been achieved by using a square pulse train produced by the intensity modulation of a cw ring dye laser in conventional intermodulated optogalvanic spectroscopy. Decreasing the pulsewidth and the repetition rate of the square pulse train, the Gaussian collisional parameter, C, for the S-1(0) --> P-3(1) transition of Yb atoms at low discharge current is reduced by two orders of magnitude when compared to that of a conventional intermodulated optogalvanic spectrum, The line narrowing of the Gaussian pedestals below the theoretical limit was also observed. Reduction of the collisional parameter as well as the line narrowing of Gaussian pedestals enhances the spectral resolution of this method and allows measurements of highly resolved Doppler-free spectra in hollow cathode discharge cells. (C) 1998 Elsevier Science B.V. All rights reserved.