Light intensity and frequency inversion of the Joshi effect

Abstract

It is shown that the Joshi effect ±δi, an almost instantaneous and reversible photovariation of the discharge current i, in halogens increases with light intensity I more rapidly at low than at large I, where it exhibits a saturation effect, the applied potential V being constant and just below or well above the threshold potential Vm. At or near Vm, +δi increases with I to a maximum; then diminishes and finally inverts to-δi. This inversion as well as the enhancement in ±δi with light frequency v is linear; the threshold frequency vm decreases with V. For a given minimum I and v, +δi inverts to-δi as V is increased progressively above Vm at the inversion potential Vi. This last decreases with I and v. The inversion with I or v occurs in the potential range Vm/Vi. The results agree with the theory that photoemission from an adsorbed layer with a low work function gives +δi per se.- δi is ascribed to a negative space charge produced near the (instantaneous) cathode. A detailed mechanism for the inversion is proposed. © 1965 Società Italiana di Fisica.