Frequency stabilization of 0.633-μm He-Ne laser using polarization modulation

A new technique is described for the frequency stabilization of an internal mirror two-mode He-Ne laser operating at 0.633 μm. The laser is placed in a small axial ac magnetic held which gives rise to polarization modulation of the two modes. The sum of the amplitude modulation produced is detected by phase-sensitive detection (PSD) and the error signal is used for frequency control. The frequency stability obtained is 1.9 × 10⁻⁹ for an integration time of 1 s.