A. B. Neilson

Unidirectional operation of ring lasers via the acoustooptic effect

Two different techniques are described for enforcing unidirectional operation of a ring laser using the acoustooptic effect. A simple quantitative explanation for each mechanism is presented, together with a detailed analytical model which allows the difference in loss for the counter-propagating beams to be calculated. Experimental results which confirm the validity of the models are also presented. The application of these techniques for single frequency CW and Q-switched operation of miniature solid-state lasers is discussed and, based on the analytical model, strategies for optimising the design of acoustooptic modulators and ring resonators are considered.

Explanation of the mechanism for acousto-optically induced unidirectional operation of a ring laser.

A mechanism is proposed for the nonreciprocal behavior of a traveling-wave acousto-optic Q switch, whose use can provide an effective way to enforce unidirectional and hence single-frequency operation of a ring laser. Simple energy and momentum conservation considerations show that the Bragg condition is satisfied at different angles of incidence for the two counterpropagating beams, which leads to a difference in their diffraction losses. The loss difference, measured directly for a diode-pumped Nd:YAG ring laser, yielded values in close agreement with calculated values. Implications of these results for both single-frequency cw and Q-switched operation of diode-pumped solid-state ring lasers are discussed.

Single-frequency cw and Q -switched operation of adiode-pumped Nd:YAG 1.3-μm ring laser

The use of an acousto-optic modulator in a ring laser to enforce unidirectional and hence single-frequency operation has been extended to the 1.3-μm lines in Nd:YAG. We have also been able to obtain stable simultaneous operation on a single frequency in each of the 1.319 and 1.338-μm transitions either cw or Q switched. The mechanism behind this behavior is described, and implications for other laser systems are discussed. When the laser is operated single frequency, as much as 155 mW of cw output is produced, and 30-μJ, 40-ns, Q-switched pulses have been obtained.

Diode laser bar beam shaping technique

A high power diode bar has been focused to a spot of <150µm diameter using a novel beam shaping technique. The implications of this result for efficient end-pumping of solid-state lasers are discussed.

Acousto-optically induced unidirectional operation of a ring laser: a feedback mechanism

Abstract A second mechanism for acousto-optically induced unidirectional operation of a ring laser has been identified and demonstrated experimentally. The mechanism involves feeding back the diffracted wave, thus restoring it to its original frequency and direction via a second diffraction from the travelling-wave acousto-optic modulator. Since the feedback resonance condition is different for the two counter-propagating waves of the ring laser, they experience a loss difference which results in unidirectional operation. Via this method a very large loss difference can be achieved with negligible insertion loss.

Unidirectional Ring Laser Operation via the Acousto-Optic Effect: An Explanation of the Mechanism

A model for the behaviour of an acousto-optically induced unidirectional ring laser is described, and measurements which confirm theoretical predictions are presented.