Non-linear effects in optical pumping with lasers. I. General theory of the classical limit for levels of large angular momenta

The optical pumping of high J levels with a broad-band CW laser is studied theoretically. Exact non-perturbative solutions are obtained by means of a Fourier development of the response of the irradiated medium. This leads to such theoretical predictions as the depolarization of the fluorescence for high laser intensities, the power broadening of the Hanle effect and the appearance of a zero-field saturation resonance in the pi fluorescence. All these theoretical predictions are finally compared with recent experiments on the optical pumping of molecules especially Na 2 and I 2 .