Long-term frequency stabilization of a composite-cavity argon laser

A commercial argon laser was modified to radiate at a highly stable single frequency over a long time period. The long-term stability is obtained by controlling the mirror separation of the mode selector cavity, using the wavelength of a stabilized He-Ne laser as a reference. As a result the argon laser emits a maximum power of 450 mW at 4880 Å with a relative frequency stability
\Delta\nu/\nu = 2.10^{-8}
over one half-hour operation.