Zeeman-birefringence He-Ne dual frequency lasers

We demonstrate an approach to obtain the frequency differences from 1MHz to hundreds of MHz including 3-40 MHz, which was a blank range of the frequency difference in the traditional dual frequency lasers. We employ an intra-cavity stress birefringence element in an He-Ne laser, and at the same time apply a transverse magnetic field to the laser. The intra-cavity stress birefringence element, which is the window plate or the mirror substrate applied by a force, is used to split a frequency into two; i.e. to make a single-frequency laser outputting two frequencies. Moreover, the transverse magnetic field is used to decrease greatly the mode competition between the two frequencies so that they are able to oscillate simultaneously. The minimum value of magnetic field for efficiently eliminating the mode competition to ensure the two frequencies work together is studied experimentally. The power tuning performance of the two frequencies (o-light and e-light) is investigated.