Solid-state laser with vibrating reflector

The temporal behavior of emission, the time-integrated spectral output, and the far-field pattern of a ruby laser have been studied as influenced by the mechanical vibrations of one of the resonator mirrors. It is shown that regular spiking with exponential decay will exist over a wide range of pump power if the following three conditions exist simultaneously: 1) one mirror is slightly tilted, or a lens or a diffusing element is inserted within the cavity; 2) radiation is retained in the resonator by use of a nearly optically closed cavity; and 3) one reflector is vibrating. In this case, the spectral output consists not of sharp lines, but of a few broad bands. Consequently, oscillation in closely spaced transverse modes is produced by the vibrating mirror. If one of the above conditions is not fulfilled, irregular spiking occurs and the spectral output contains sharp lines whose frequencies are multiples of the axial mode spacing and whose number depends directly upon the pump power. Regular spiking permits an experimental test of theoretical models. The plot of the decay time of the regular spiking envelope versus normalized pump power has ascending and descending branches and is in excellent agreement with the expanded Statz-de Mars theory, which takes into account a large mode number and the influence of spontaneous emission. Parameter of the family of curves is the ratio : number of existing resonator modes to total number of possible modes (for the same bandwidth) that is approximately equal to the solid angle of laser radiation divided by the solid angle 4 π. Finally, the experimental values for the period of the spike train agree so well with theory that they can be used to determine the total mode number and the Einstein coefficient .