SPECTRAL-LINE SHAPE OF RESONANT 4-WAVE-MIXING INDUCED BY BROAD-BANDWIDTH LASERS

We present a theoretical and experimental study of the line shape of r esonant four-wave mixing induced by broad-bandwidth laser radiation th at revises the theory of Meacher, Smith, Ewart, and Cooper (MSEC) [Phy s. Rev. A 46, 2718 (1992)]. We adopt the same method as MSEC but corre ct for an invalid integral used to average over the distribution of at omic velocities. The revised theory predicts a Voigt line shape compos ed of a homogeneous, Lorentzian component, defined by the collisional rate Gamma, and an inhomogeneous, Doppler component, which is a square d Gaussian. The width of the inhomogeneous component is reduced by a f actor of root 2 compared to the simple Doppler width predicted by MSEC . In the limit of dominant Doppler broadening, the width of the homoge neous component is predicted to be 4 Gamma, whereas in the limit of do minant homogeneous broadening, the predicted width is 2 Gamma. An expe rimental measurement is reported of the line shape of the four-wave-mi xing signal using a broad-bandwidth, ''modeless,'' laser resonant with the Q(1)(6) line of the A (2) Sigma-X (2) Pi(0,0) system of the hydro xyl radical. The measured widths of the Voigt components were found to be consistent with the predictions of the revised theory.