Solid-state laser gyro using ZnS for Kerr-lens mode locking

Abstract

The beat note between counterpropagating beams in a ring cavity is a measure of its angular velocity. A major limitation of current laser gyros is the coupling (through scattering) between the counterpropagating waves, resulting in a zero response or dead band at low rotation rates. We have shown that the lock-in problem can be avoided with ultrashort-pulse lasers, where the two counterpropagating pulses meet in only two places (both outside the gain medium), providing minimal opportunity for coupling to occur. For practical reasons, a pure solid-state laser gyro would be preferable to a dye laser or a gas laser. Homogeneously broadened lasers tend to be unidirectional, and even the mode-locked Ti:sapphire ring laser is no exception. However, through the use of an intracavity energy limiter, we have shown that it is possible to achieve bidirectional operation of a Kerr-lens mode-locked Ti:sapphire laser, at the expense of a very large bias beat note. We demonstrate here bias-free bidirectional operation of a Ti:sapphire laser, through the use of a ZnS crystal as Kerr-lensing element. The bidirectional operation is a result of mutual Kerr lensing in the ZnS.