Quantum efficiency, intrinsic emittance, and response time measurements of a titanium nitride photocathode

Abstract

The photoemission properties of photocathodes affect the ultimate performance of electron accelerator based facilities and the cost. Several major properties of titanium nitride (TiN) irradiated by ultraviolet femtosecond laser pulses were studied. Specifically, the quantum efficiency and intrinsic emittance were measured, and the response time was estimated indirectly. For photon energies higher than the work function, quantum efficiency values of $7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}--5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ were obtained. The measured intrinsic emittance was $0.54\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{mm}$ for the typical wavelength of 266 nm (4.66 eV). When the photon energy was lower than the work function, two-photon photoemission appeared, and the intrinsic emittance increased with the laser intensity. At photon energies of higher than and slightly lower than the work function, the intrinsic emittance ranged from 0.28 to $0.60\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{mm}$ and tended toward a minimum constant of $0.28\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{mm}$ if only single-photon photoemission was considered. The response time of TiN was proven to be close to that of gold by comparing the transverse expansion of electron beams under space charge force for the irradiated photon energy higher than the work function. The autocorrelation measurement of the photoemission of TiN and gold were performed, and a comparison of these results indicated that the two-photon photoemission of TiN excited by a photon energy slightly lower than the work function was prompt.