The measurement of spin-lattice relaxation times at very low power levels

Spin-lattice relaxation times in ruby and sapphire have been measured at 35 and 70 Gc/s by a pulse-response technique using a grid-modulated reflex klystron, the peak pulse power at the specimen being about 10 μW. Relaxation times at 42°K covering the range from 2 msec to 24 msec have been measured at 35 Gc/s, the results in each case agreeing with those obtained from pulse-saturation measurements on the same specimens. Preliminary data are given of the relaxation in ruby at 70 Gc/s, the microwave power being obtained by harmonic generation from 35 Gc/s. The range of applicability of the method is discussed.