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Parallel plate analyzer with Au mesh. The analyzer measures the photoemission current over a 2π solid angle as a function of the retarding potential to determine the electron energy spectrum.
Comparison of the energy spread of an uncoated single crystal (100) copper photocathode with the single crystal (100) Cu photocathode coated with a 25 A CsBr film when illuminated with a 8 mm CW 257 nm laser beam and a power density of ∼3 W/cm2. (a) Energy spread raw data corrected by the ratio of QE's of CsBr/Cu (4.5 × 10−4) and uncoated Cu 100 crystal (2.8 × 10−5). (b) Same as (a) but with peaks normalized to unity. (c) Error function shaped data obtained with the energy spread analyzer shown in Figure 1 . The energy spread of the uncoated copper sample is 0.31 eV, and the energy spread of the CsBr/Cu sample is 0.77 eV, both obtained from the FWHM of the derivative curve.
The quantum efficiency as a function of the effective work function for an incident photon of 4.826 eV. The QE has been computed with two sets of parameters for the reflectivity, optical absorption length, and electron scattering length to estimate the systematic error of the effective work function.
Calculated intrinsic emittance for Cu and CsBr/Cu photocathodes.
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