Frequency stabilization of the FM laser

A technique for the frequency stabilization of an FM laser is discussed. This technique employs a stabilization discriminant derived from a residual variation of the phase and amplitude of the small FM laser beat note at the modulation frequency, as the frequency of the FM carrier moves across the Doppler gain profile. A first-order analysis describes the dependence of that stabilization discriminant on δ, the mode coupling coefficient produced by the internal KDP phase modulator, and Γ, the resulting FM modulation index. Experimentally, a 50-mW He-Ne FM laser was frequency stabilized to better than one part in 10⁸on a long-term basis. In addition, the beat note at the modulation frequency was suppressed by 40 dB from its free-running value.