Intensity Tuning Characters of Frequency Split Lasers

Laser frequency splitting generated by intracavity birefringence elements has been applied widely, but tuning characters of such lasers have not been successfully studied quantitatively. Based on the vectorial extension of Lamb's semi-classical theory, we study the intensity tuning of frequency splitting of He--Ne lasers. It is found that the intensity tuning curve is affected obviously by the compositive ratio of isotopes in the gain medium and the frequency difference of splitting modes. The threshold of locking is also quantitatively obtained. All the calculations are consistent with the experimental results.