Observation of sub - Poisson Franck - Hertz light at 253 . 7 nm

We report the generation of ultraviolet (253.7-nm) sub-Poisson light from Hg vapor excited by inelastic collisions with a space-charge-limited (quiet) electron beam. This first stationary sub-Poisson light source is only weakly so, with a Fano factor that is between two and three standard deviations below that for Poisson light. This is principally because of optical losses in the experimental apparatus. There does not appear to be any fundamental limit that impedes the techniques from being used to produce an intense cw light source that is also arbitrarily subPoisson.