The correlation between frequency difference and mode polarization in an intracavity birefringent dual-frequency laser

We discuss the correlations between the measured lasing-mode frequency difference and the mode polarization angle in an intracavity birefringent dual-frequency laser. The frequency difference and polarization are adjusted by rotating an intracavity quartz crystal through a large angular range. We propose two kinds of frequency difference: the equal-order frequency difference and the adjacent frequency difference. By measuring the equal-order frequency difference versus the quartz crystal rotation angle, the real physical process behind frequency splitting is revealed. Based on this, the adjacent frequency difference curve is also obtained. The emitted laser beam polarization angle is also measured for large rotations of the intracavity quartz crystal. These measurements reveal the complete process of optical activity in frequency splitting and allow us to predict the trends of frequency difference and polarization angle for large quartz crystal rotation angles. We analyze the correlations between the equal-order frequency difference and the polarization angle based on the experimental results, which show that the certain points on the two curves are inter-related. The principal results agree well with the optical theory of crystals.