Patent Number: 5,091,913
Date of Patent: Feb. 25, 1992
QUARTZ CRYSTAL TUNING HE-NE DOUBLE FREQUENCY LASER
A birefringent quartz plate is inserted in the laser cavity to generate two orthogonal polarized beams with different frequencies, and with the amount of frequency difference depending upon the angle of orientation of the crystalline axis of the quartz plate with respect to the longitudinal axis of the laser beam in the cavity. Frequency differences between the generated dual frequency beams can be varied from tens of MHz to more than 1000 MHz, with tuning or variation being effected by a mechanism for rotating the quartz plate. This apparatus provides a dual frequency laser for interferometry, laser Doppler velocimeters and other applications.