  We present a clear signature of the Schottky effect in a RF photoinjector
using photons with energy lower than the Mg cathode work function. This
signature is manifested by the shift in the RF phase angle for the onset of the
detection of photoelectrons via single-photon absorption and allows for a
reasonable estimate of the field enhancement factor. This is a viable method to
generate an electron beam with very low thermal emittance and thus, a high
brightness beam.
