Hybrid injection locking of higher power CO<inf>2</inf>lasers

Abstract

Frequency stabilization of a higher power CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ring laser by locking with a stable low-power reference laser is described. Successful locking is achieved by employing a novel hybrid injection-locking technique. In the hybrid mode, the higher power laser is tuned to operate on a self-oscillation line different from that of the reference laser. Within the frequency-locking range, the self-oscillation of the locked laser is completely quenched, and only the amplified drive power of the locking laser appears. Operation of this hybrid technique relies on the line competition in the homogeneously broadened CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> medium. The hybrid technique, which is easily implemented with a simple hill-climbing servo, permits stabilized operation over a variety of laser lines. An analysis of injection locking that explicity includes the saturation of the homogeneous medium is presented. Expressions are obtained for the gain and the phase relationships within and outside the locking region. To demonstrate the potential of the hybrid injection-locking technique, a 60-W CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser was locked in frequency to a 0.5-W stable oscillator. The experimental data are in close agreement with theory.