Infrared emission at 1093 nm from sodium is observed when the vapor is excited by pulsed dye laser beam. The excitation source is an excimer laser pumped dye laser with laser wavelength tuned to the two-photon resonance of sodium 3s-5s transition. The sodium vapor is confined within a heatpipe oven with a 50Torr argon buffer gas pressure. There are two parts in the observed emission spectrum. With the excitation photon energy below two photon resonance, the observed emission has fixed wavelength irrelative to the laser wavelength change. While the laser photon energy is tuned beyond the two-photon resonance, the infrared emission becomes tunable associated with the laser wavelength tunning. The tunable part of this emission can be explained by a six-wave mixing process. We suggest the fixed wavelength part be ascribed to a parametric wave mixing process. Calculation of phase match condition agrees very well with this assumption. Excitation bandwidth at high temperature has no significant broadenning shows that there is no molecular process involved in generating these infrared emissions.
