PROMPT AND PRECISE FREQUENCY TUNING OF A TRANSVERSELY EXCITED CO2-LASER BY MEANS OF INTRACAVITY ACTIVE FREQUENCY-SHIFT

We have investigated the tuning characteristics of an injection-locked transversely excited CO2 laser by means of intracavity active frequen cy shift which utilized an acousto-optic modulator and a Pockels cell inside the cavity. The frequency shift from the externally injected fr equency was finely controllable as a linear function of the gated time for integration of acousto-optic frequency shift. The maximum frequen cy shift obtained was 2 GHz, which was limited by the pressure-broaden ed gain bandwidth of the laser medium. A numerical model was used to v erify the characteristics of this technique and to explore the possibi lity of further shifting the frequency by increasing the pressure of t he laser medium. Single-longitudinal-mode oscillation was obtained whe n the gate pulsewidth was a multiple of the round-trip time in the sub cavity. Finally, prompt response by electrical control of the lasing f requencies was demonstrated in alternative frequency switching operati on.