Nonlinear optical generation of radiation near the frequency of the third harmonic of an iodine laser

Nonlinear optical generation of the third harmonic in the vapour of a metal at a frequency close to the tripled frequency of an iodine laser was achieved for the first time. Phase-matching conditions in the presence of a buffer gas and the nonlinear susceptibility were close to the calculated predictions. A change in the energy of the third harmonic pulses with time was observed in a cell with cooled windows and a mechanism explaining this effect was proposed. The effect could be eliminated in an all-heated cell with better operational characteristics.