Speaker
Description
Photocathodes with higher polarization and quantum efficiency (QE) can significantly enhance
the physics capabilities of electron accelerators. In this submission, we describe the characteristics
of strained GaAs/GaAsP superlattice photocathodes fabricated with a Distributed Bragg Reflector
(DBR). The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of
strained-superlattice photocathodes by increasing the absorption of the incident photons using a
Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that
includes a DBR, without compromising electron polarization. A typical strained GaAs/GaAsP
superlattice photocathode provides polarization near 90% and QE ∼ 1%. Simulations suggest that
a properly fabricated DBR photocathode structure will increase QE by a factor of five. Presently,
we measure a polarization of 90.7% but only 0.92% QE at the laser wavelength of 780nm. We
continue to try to enhance the QE beyond the nominal 1% value by optimizing the DBR structure.
