Mode-locked dual-polarization operation of a CO2laser

An electrooptic mode-locking technique for inducing simultaneous oscillation of spacially congruent, orthogonally polarized CO
2
laser modes is described. During mode-locked dual-polarization operation the frequency separation of the output components is determined by the magnitude of an intracavity birefringence. It can therefore be adjusted to any value consistent with the gain-profile width. The sensitivity of the technique is such that for intermode frequencies between 1 and 20 MHz, a
3 \times 10^{-4}
radian intracavity phase modulation suffices to produce continuous, stable dual-polarization operation. Experimental results are given that indicate the dependence of the mode-locking phenomenon on modulator drive, intermode frequency, and laser cavity tuning. These results are compared with the prediction of simple theory.