Cross-Relaxation Effects in a Ruby L?Band (1440 Mc/s) Maser at Low Magnetic Fields

Abstract

The reversals of maser behaviour which occur in ruby at low fields on cooling from 80° to 4 oK are explained in terms of cross-relaxation transitions (resonant interchanges of energy between neighbouring paramagnetic ions). For an angle of 29° between the magnetic field and the crystal axis a cross-relaxation process has been demonstrated which involves groups of three ions and has a transition probability of 700± 100 per second in 0·013% ruby. The profile of the cross-relaxation resonance has a half-width of 190±30 Mcts at half-intensity, and has an approximately Gaussian shape. It should be possible to obtain useful low-field L-band maser action at 4 oK by pumping V41 with the magnetic field nearly perpendicular to the crystal axis, and also at 80 oK using a concentration ten times higher, i.e. 0·13%