Theoretical and Experimental Investigation of Coupled Ar-Ion Lasers.

A single-mode laser theory was applied to two coupled Ar-ion lasers in Fabry-Perot resonators and the equations were solved numerically to predict intensity tuning curves and locking ranges for various types of mirror translations. The same theory was extended to model two modes in each cavity, which predicted a decrease in locking range as well as a mutually-reinforced hole-burning minimum. With a single, uncoupled, two-mode He-Ne laser, the existence of the minimum was verified experimentally. Two multiline/multimode Ar-ion lasers were coupled through a common end mirror and the effect of coupling strength on phase locking was investigated by varying the reflectivity of that mirror. In order to characterize the phase-locked performance of multiline/multimode and single-line/multimode coupling, interference fringe visibilities, output power, and frequency and RF mode beat spectra were measured. It was found that the optimal phase locking occurred at approximately 25% coupling as determined by the maximum fringe visibilities produced by laser phase locking. That 25% coupling was the optimum coupling strength was also substantiated by the fact that the maximum power output was also achieved at this point, and the appearance of the super cavity mode spacing verified that the behavior was due to phase locking. A passive cavity mode analysis of the three-mirror Fabry-Perot resonator showed that the system oscillated on the composite resonator frequency as well as the frequencies of both subresonators.