Hybrid injection locking

A new injection-locking technique for frequency stabilizing CO2laser oscillators is discussed. In contrast to more conventional injection locking, in which the injected signal pulls the laser oscillation into phase, in hybrid operation the drive signal is applied to a wavelength which does not oscillate because of competition with higher gain transitions. With the aid of the injected signal, oscillation switches to the frequency of the injected signal and its normal oscillation is completely quenched. This hybrid stabilization is inherently flexible and allows frequency stabilized operation on a large number of lines. Furthermore, the difficult to implement optical phase comparison technique required by ordinary injection-locking approaches is replaced by a simple amplitude discriminant. To demonstrate the potential of this technique, a 60 W sealed-off CO2laser was locked in frequency by the injection of a 0.5 W signal. Expressions for the frequency locking range, the extracted power and the gain-bandwidth product are derived as a function of injected power, the undriven laser power, and the resonator coupling. Experimental data in agreement with theoretical analysis are presented.