Abstract

A vacuum photodiode is the most elementary photoelectric detector. Photons impinge on a photocathode in vacuum. A nearby anode collects photoelectrons from the cathode and the resulting photocurrent is measured in a suitable external circuit. Such a device is sensitive to photon energies which exceed the photocathode work function in accord with the classical photoelectric effect. Photocathode materials with high quantum efficiency (1-30%) have been developed for use at optical wavelengths shorter than ~1µm. For vacuum ultraviolet and soft X-ray radiation, photoelectric quantum yields in excess of 50% can be reached.¹ With a carefully designed external circuit, the response time of such a detector is limited by the diode capacitance. The present state-of-the-art risetime in a commercial biplanar vacuum photodiode² is 0.09 nsec.

© 1988 Optical Society of America