Use of MgF(2) and LiF Photocathodes in the Extreme Ultraviolet

The photoelectric yields of 2000-A thick samples of MgF(2) and LiF have been measured at wavelengths in the range 1216-461 A. Peak values of 43% and 34%, respectively, were obtained at wavelengths around 550 A at 45 degrees incidence. Coating the cathode of a channel electron multiplier with 3000 A of MgF(2) 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 A, 584 A, and 461 A, respectively. Since the stability of response of the MgF(2) photocathodes appears to be equal to that of conventional metallic and semiconducting cathodes, it is concluded that MgF(2) would be a practical, high-efficiency photocathode for use in the extreme uv.