Simple technique for the detection of oscillation at 3.39 µ in a He-Ne laser operating at 632.8 nm

A simple technique is reported for determining if oscillation is occurring simultaneously at 3.39 μ and 632.8 nm in a He-Ne laser. It relies on observation of modulation of the output power at 632.8 nm when a variable path length element is introduced into the optical cavity of the laser. The technique is applicable to other gas laser systems where competition for upper level populations occurs between transitions at widely differing wavelengths.