Use of MgF_2 and LiF Photocathodes in the Extreme Ultraviolet

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Abstract
The photoelectric yields of 2000-Å thick samples of MgF2 and LiF have been measured at wavelengths in the range 1216-461 Å. Peak values of 43% and 34%, respectively, were obtained at wavelengths around 550 Å at 45° incidence. Coating the cathode of a channel electron multiplier with 3000 Å of MgF2 produced no significant deterioration in the electrical properties and increased the sensitivity by factors of 1.62, 2.76, and 2.60 at wavelengths of 742 Å, 584 Å, and 461 Å, respectively. Since the stability of response of the MgF2 photocathodes appears to be equal to that of conventional metallic and semiconducting cathodes, it is concluded that MgF2 would be a practical, high-efficiency photocathode for use in the extreme uv.