Relaxation mechanisms in maser materials

Abstract

Measurements have been made using a pulse saturation technique at 35 Gc/s of the relaxation times for transitions within the ions of the ‘irongroup' of transition metal elements placed in various lattices. A microwave spectrometer has been constructed in which the need for a separate local oscillator source has been overcome. A detailed study of the relaxation times and the texture in ruby single crystals has shown that the relaxation depends on the c-axis misorientation within the crystal, but is independent of the mosaic structure. A study of the temperature dependence of the relaxation times from 1.5 K to 120 K has shown that the chromium ions occupy two types of site within the lattice, one perfect the other distorted. Similar results have been obtained for samples of ruby grown by Verneuil and Gzochralski techniques. The effect of impurities in ruby has been considered and a 'figure of merit' has been empirically devised to describe the effects of cross-relaxation between chromic and ferric ions. X-irradiation of rubies has given indirect evidence for the existence of the Cr(^2+) ion. A brief examination of the relaxation times in chromium doped spinel and rutile has led to an explanation of the frequency dependence of the relaxation times for transitions across the lower Kramer's doublet in terms of an Orbach process. An examination of three alums has supported the suggestion of Kochelaev that the relaxation process in these materials is governed by the vibrations of the water complex surrounding the paramagnetic ion.