Quantum efficiency of technical metal photocathodes under laser irradiation of various wavelengths

Abstract

Quantum efficiency studies for various wavelength and various technical metal surfaces were carried out in a dedicated unbaked vacuum chamber. Copper, magnesium, aluminium and aluminium-lithium photocathodes were irradiated by two different high power, high repetition rate, laser systems. We have observed an emission of electrons for photon energy below the work function of the material. This is explained by multiple photon absorption at the photocathode. We have not observed any degradation of the QE for those materials, but an improvement when irradiating them over a long period of time. This is contrary to observations made in RF photoguns.

Photoemission simulation for photocathode design: theory and application to copper and silver surfaces

“…They are, nevertheless, in general agreement with measurements of the absolute QE made on these metals. These range between 10 −6 and 10 −3 measured for polished and mirror like samples in vacuum [36]. This is in reasonably agreement with the quantum efficiency simulated in this work.…”

“…copper and silver samples, respectively calculated using linear-muffin-tin-orbitals Green'sfunction theory [29]. From photoemission experiments work function values between 4.3 eV and 5.1 eV for copper and between 4.2 eV and 4.7 eV for silver have been deduced [36][37][38].…”

Growth of poly-crystalline Cu films on Y substrates by picosecond pulsed laser deposition for photocathode applications

“…In that context, different metals like Pb, Cu, Al, Al-Li, W, Au or Fe have been extensively studied, and their application in implemented photocathode applications has been evaluated [17][18][19][20][21]. From the reported studies, it has been pointed out that yttrium (Y) and magnesium (Mg), due to their superior performance [12][13][14][15]22,23], seem to be the most promising metallic materials for the fabrication of photocathodes.…”

Photoemission and degradation of semiconductor photocathode

“…4, both QE and the intrinsic emittance with photon 1.9 eV get an improvement compared with those with photon 1.8 eV. It is a very interesting result for the intrinsic emittance, since the conventional formula (MTE ¼ ðℏω − E g − E a Þ=3) expects a higher intrinsic emittance with 1.9 eV photon [49,50]. The examples suggest that the acceptor level plays an important role in threshold photoemission at room temperature and the ratio between the contribution from the valance band and the acceptor level is sensitive to the working condition.…”

“…When the oxide layers reach the maximum thickness d max , the chemical robustness of the cathode is expected to be similar to the metal and a comparable lifetime is possible. It should also be noted that the lifetime of cathodes in the rf gun is affected by other factors as well, like laser and rf field [50]. Their influence on Cs 3 Sb is not clear and more efforts should be devoted into the lifetime study experimentally.…”