Frequency Response of the 6328‐Å Helium‐Neon Laser Interferometer

The speed of response of a 6328‐Å helium‐neon laser interferometer has been investigated under various conditions of operation. The laser oscillated in a small number of modes (all TEM₀₀). At low output levels, the bandwidth of the interferometer was proportional to the output power, and except very close to threshold was not unduly affected by variation of the output spectrum. For values of the excitation parameter η (the ratio of unsaturated line‐center gain‐to‐loss) between 1.0 and 1.25, the bandwidth f₀ was approximately $$f_0\text{≃[(η−1)/1.7η](J/2π)}$$ , where J is the fraction of the radiation energy lost per second from the cavity. The observations are interpreted in terms of loss modulation, taking into account the coupling between the intensities in the various modes of oscillation. The results obtained are equally applicable to other examples of loss modulation.