Power-Dependent Frequency Shifts in Ruby Lasers at 77°K

Abstract

Ruby lasers, when operated near threshold at 77°K with a low Q cavity (one end silvered for maximum reflectivity and the other end uncoated) oscillated at two frequencies. The frequency differences near threshold, measured with Fabry-Perot etalons, were in good agreement with the splitting of the R1 doublet, previously measured by microwave methods. As the power of the laser increased, the frequency difference between the oscillating components [2Ē → 4A2(±32, ±½)] decreased. These results are accounted for on the basis of saturation broadening of overlapping Lorentzian lines. The observed variations in the splitting are in good accord with the theory. The rise in temperature of the ruby rods produced a negligible change in the splitting of the R1 doublet. The same mechanism which produces the variation in the splitting should broaden the output spectrum of the laser.