Ne absorption tube in an alternating magnetic field inside a laser cavity as a frequency standard

A neon absorption tube placed in an alternating magnetic field is used as a frequency standard for the frequency stabilization of a He-Ne laser. This absorption tube, which is situated within the laser cavity, permits a very precise frequency adjustment (<10^-12) due to the formation of the inverse Lamb dip. An excellent beam coherence is also obtained because this method of stabilization does not superimpose any frequency modulation on the oscillation.