Characterization of CsI photocathodes at grazing incidence for use in a unit quantum efficiency x-ray streak camera

Abstract

The performance of CsI photocathodes has been characterized for use with grazing incidence soft x rays. The total electron yield and pulsed quantum efficiency of a CsI photocathode has been measured in a reflection geometry as a function of photon energy (100 eV to 1 keV), angle of incidence, and the electric field between the anode and photocathode. The total electron yield and pulsed quantum efficiency increase as the x-ray penetration depth approaches the secondary electron escape depth. Unit quantum efficiency in a grazing incidence geometry is demonstrated. A weak electric-field dependence is observed for the total yield measurements; while no significant dependence is found for the pulsed quantum efficiency. The effect of the pulse height distribution on the detective quantum efficiency is discussed. Theoretical predictions agree accurately with experiment.

Secondary Electron Cascade Dynamics in KI and CsI

“…Still missing in our approach is a proper treatment of the low-energy regime, where phonon scattering becomes significant for the energy loss of the SEs. 20,22,26 Since our main objective is to compare the characteristics of the electron cascades generated in KI and CsI, we have, for the sake of simplicity, not included the treatment of holes. The average electron-hole pair creation energy is given by the ratio between the energy deposited in the system and the total number of SEs generated.…”

“…This discrepancy was claimed to arise from the lack of treatment of plasmons in their model. 28 A recent investigation on the efficiency of CsI as a photocathode in a streak camera with gracing incidence geometry was presented by Lowney et al, 20 where the unit quantum efficiency between SEs generated inside the material and the number of escaping electrons was demonstrated for photon energies between 100 eV and 1 keV.…”

“…The streak camera's resolution and efficiency is thus determined by the total electron yield and its spread in energy. [18][19][20] Kane 21 presented a first derivation for the rate of inelastic scattering of electrons by considering the production of electronhole pairs in silicon. Henke et al 22 performed further investigations for semiconductors and insulators as compared to gold, both theoretically and experimentally, with respect to the electrons' total yield and their distribution in energy.…”

High quantum efficiency photocathode simulation for the investigation of novel structured designs

“…The X-ray yield increase seen at grazing incidence has been verified experimentally, 6 and a model has been developed by Fraser et al, which accurately predicts the increase in total electron yield as a function of angle of incidence and photon energy for the majority of commonly used photocathodes. 8 We now introduce a simplified version of Fraser's derivation with assumptions most relevant to the 1-10 keV X-ray range.…”

“…[3][4][5] Most X-ray detectors operate at normal incidence, i.e., X-ray photons are at a 90 • incidence angle to the photocathode, and suffer a loss in quantum efficiency at energies greater than 5 keV. Improvements in yield of up to 20 times 6 have been shown to occur in grazing incidence geometry due to a larger path length of the X-ray photons which better matches the secondary electron escape depth within the photocathode material. [7][8][9][10][11] This work describes the details and results of a simulation used to identify a set of potential photocathode designs that leverage the grazing incidence geometry yield improvements through the introduction of pillars or cavities to the photocathode substrate surface.…”