Parametric four-wave mixing in Kr is described. When the 5p levels of
Kr were excited by two-photon absorption of pulsed UV laser radiation,
near-infrared radiation corresponding to 5p --> 5s, as well as a reso
nance line at 123.6 nm, were observed. It was demonstrated that both n
ear-infrared and vacuum ultraviolet emission were highly directional.
Polarization properties of near-infrared radiation are presented.