Microwave Inversion Efficiency of Orange Ruby

Abstract

RECENTLY some ruby, grown by a vapour-phase process, has been found to be orange coloured rather than the normal pink. Some of this has been investigated as a potential maser material by taking a small sample (∼ 10 mg), containing 0.05 per cent Cr³⁺, double pumping at 23 kMc/s and observing the resulting inversion of the 2–3 transition at 9 kMc/s (Fig. 1). This was then compared with the inversion obtained from a sample of pink ruby of similar size and concentration, placed in the microwave cavity, alongside the orange ruby. The c axes of the two crystals were arranged to be at 90° to each other and at 45° to the radiofrequency magnetic field in order to achieve similar transition probabilities. The inversion ratio I, defined as: when measured at 1.4° K, was found to be 1.5 for the pink ruby, while that of the orange was much bigger, being of the order of 5.0 for most samples.