Laser-Induced Two-Photon Blackbody Radiation in the Vacuum Ultraviolet

We report experimental measurements on a new type of vacuum-ultraviolet radiation source. It is shown that the maximum source brightness, within its narrow linewidth, is that of a blackbody at the temperature $T$ of a metastable storage level. The laser-induced emission at 569 Å from a He glow discharge corresponded to a metastable temperature of 22 700°K and was over 100 times brighter than the 584-Å He resonance line.