A 5 MHz beat frequency He-Ne laser equipped with bireflectance cavity mirror

A He-Ne dual-frequency laser equipped with a bireflectance cavity mirror is described. It is based on the principle that when the incident light is perpendicular to the bireflectance cavity mirror, the phase delays of the reflective light along the mirrorʹs fast and slow axes are different because of the photoelastic effect. The mode coupling is reduced by utilizing transverse Zeeman effect so that two linear and orthogonal polarization components with 5 MHz beat frequency are generated. The effect of the magnetic fieldʹs direction on the dualfrequency as well as the polarization property of the laser are investigated by experiments. After stabilizing the frequency, the laser is calibrated with the iodine frequency stabilization laser of Chinese National Institute of Metrology (CNIM). Experimental results indicate that the expanded uncertainty of wavelength in vacuum is 1×10-7 (k=3) with a frequency stabilization of 6.6×10-10 (sampled in 1000 s).