Emittance of a photocathode: Effects of temperature and field

University of Maryland, College Park, Maryland 20742-3511, USA(Received 22 February 2010; published 5 August 2010)The emittance of a photocathode is evaluated using a distribution function (‘‘Moments’’) approach tocalculate the moments of the momentum. The effects of temperature and field, which affect the electrondistribution and transmission probability, respectively, of electrons incident on the surface barrier, arefound. The resulting formulations of emittance are compared to the asymptotic limit found by D.H.Dowell and J.F. Schmerge [Phys. Rev. ST Accel. Beams 12, 074201 (2009)], and their formulation isshown to be more generally applicable than the approximations within it would indicate for metals. Themethodology is extended to develop an asymptotic emittance estimate for semiconductor photocathodes.