Active q-switched high power single mode laser

Abstract

A high power single mode laser is disclosed which includes a Q-switch for switching the laser on in two stages: firstly, to a relatively high loss level just above threshold where it is held to permit a train of relaxation oscillator spikes to be established and then it is switched to a second stage in which the Q-switch is in a lossless state to allow the resonant mode within the laser to build up to maximum power. An optical detector monitors the resonant optical radiation level within the optical resonator and produces an output signal for each of the relaxation spikes. A trigger circuit, responsive to the detected oscillator spikes, triggers the Q-switch so as to switch it to the second or lossless state upon receipt of the second or any other subsequent relaxation oscillator spike, whereby single longitudinal mode operation of the laser is enhanced. A pair of quarter wave plates are disposed on opposite sides of the laser gain medium within the optical resonator to make the power density distribution within the laser gain medium more uniform, thereby further enhancing single longitudinal mode operation. In a preferred embodiment, the trigger circuit includes a divider which is responsive to the detected oscillator spike signals and divides the received spike signals by two or more so that the laser is caused to fire upon initiation of the second or subsequent relaxation oscillator spike.