Nonlinear absorption of coherent resonance radiation in pink ruby

A high resolution study has been made of the R(1) doublet in the absorption spectrum of pink ruby, using a temperature-controlled ruby laser as a variable frequency monochromatic source. The source and sample crystals were oriented for measurement of the absorption of alpha-polarized radiation, and the measurements were made near liquid nitrogen temperature. The observed absorption coefficient was found to decrease as the intensity of the incident beam was increased, indicating that significant depletion of the ground state was effected by the resonant pumping action of the laser beam. The highest laser beam intensity employed was approximately 100 J/cm(2). At this intensity level a significant reduction in the spectral spacing of the R(1)(+/-3/2) and R(1)(+/-(1/2)) components of the absorption doublet was also observed. Time-resolved spectral measurements showed, moreover, that at similar intensity levels, temporally smooth incident beams at frequencies near the absorption line peaks emerged from the sample temporally structued. The observed reduction in the absorption coefficient agrees well with calculations based on a simple model for ground state depletion, but no detailed theoretical explanation of the other observed phenomena has yet been developed.