Modulation and mode locking of the continuous ruby laser

The continuous ruby laser is operated with an external mirror; a modulating crystal (KDP) and a Brewster plate as polarization switch are used in the inner beam path. Coupling of the axial laser modes occurs if the frequency of a voltage applied to the KDP crystal equals
c/2L
(=30 MHz). Instead of assuming equal mode intensities, these intensities are calculated from the condition of a minimum of the total losses in the resonator. It is found that these intensities differ largely in their magnitudes. A curve calculated for six locked modes corresponds exactly to the measured emission curve. If a modulating frequency other than the frequency separation
c/2L
between adjacent longitudinal modes is chosen, the effect of the modulation on the stored energy within the laser averages out. Nevertheless, the intensity coupled out at the Brewster plate is modulated according to the term
(\varphi_{1} + \varphi_{0} \cos\Omega t)^{2}
. Some results of this coupling modulation are presented.