Abstract: Frequency stabilization is disclosed for a two-mode laser, such as a Zeeman aser. The emission frequency of the laser is servo-stabilized to the center of the atomic gain curve to provide a stable laser reference frequency that is independant of time and enviromental operating conditions. Stabilization in a longitudinal-field Zeeman laser is achieved by utilizing the mode-pulling effect which makes the frequency difference between the two circular polarization components have a parabolic dependence on the optical frequency of the laser. The detected intermode beat frequency from the laser is subjected to digital phase-sensitive, drift-free integration, utilizing a reversible counter, to provide a cumulative count with a rate of increase corresponding to the displacement of the average wavelength from the atomic center wavelength and an analog error-correction signal is generated therefrom which is coupled to the laser.

Abstract: A laser beam flow tube arrangement is disclosed in which the Ranque-Hilsch effect is advantageously utilized to reduce thermal blooming in a laser beam. The arrangement includes a tubular member through which the laser beam is propagated longitudinally and a vortical flow generator in gas flow communication with the interior of the tubular member. The flow generator produces vortical flow of a gas having low absorption properties at the wavelength of the laser beam and introduces the vortically flowing gas into the tubular member. The gas flows along a helical path within the tubular member with a tangential velocity selected to provide a negative temperature gradient between the wall and axis of the tubular member which is substantially equal in magnitude to the positive temperature gradient therebetween due to the thermal blooming.