Spectral characterization of a Rh(110) photocathode: Band structure interpretation

The spectral dependence of the mean transverse energy and quantum efficiency of photoemission from a single-crystal Rh(110) photocathode are determined at 300K using the solenoid scan technique and a sub-picosecond laser-based UV radiation source tunable from 3.0-5.3eV (235-410nm). The tunable UV radiation is generated by sum frequency mixing the second and third harmonics of a front-end, 2W, 28MHz repetition rate, femtosecond Yb:KGW laser with signal and idler radiation from nonlinear-fiber continuum-seeded optical parametric amplification. The measured properties of the Rh(110) photocathode are well explained by a one-step photoemission simulation employing the dispersion of the emitting Σ1 and Σ2 bulk band states evaluated by fully relativistic (including spin-orbit coupling) Ab initio density functional theory methods and an exact quantum solution for transmission through and over a triangular barrier that is extended into the transverse dimension. The inclusion of the joint density of states (bulk crystal and vacuum) in the simulation accounts for the observed spectral dependence of both the mean transverse energy and the quantum efficiency of the photoemission process. The consequent demonstrated base line for the evaluation of photocathode emission properties using Ab initio methods will allow for the development of screening tools to select promising (ultra)low emittance solid-state photocathodes.