【摘要】The two longitudinal modes whose polarizations are orthogonal to each other can appear in the resonant cavity of He-Ne laser cavity 140mm long with. The both modes compete each other. Controlling the resonant cavity length, the heater wrapped on it enhances the output power of the weakening mode so as to stabilize the frequencies of the both modes. The intracavity laser includes a laser resonant cavity, a heater, an analyzer, a polarized spectroscope, and two detectors. The voltage multiplying rectifier circuit is designed for the laser power. When the frequencies of the both modes are stable, the positive duty of the output pulse of the comparator is 50%. With the beat frequency method, the frequency stability of this laser is tested for 2 x 10~(-10). The laser using this method has a lot of particular advantages that other methods do not possess, such as no piezocrystal or magnetic field.