A study of a two-frequency NMR maser

Abstract

A unique NMR maser has been developed and operated which oscillates continuously and simultaneously at two different Larmor frequencies. The nuclear spin systems consist of hydrogen and fluorine nuclei provided by a 10 cm('3) sample of benzene and hexafluorobenzene. Overhauser pumping is used to invert and enhance the two nuclear magnetizations. A magnetic field of 11.74 gauss is used so that the oscillation frequencies are 50.00 kHz (the hydrogen nuclei Larmor frequency at 11.74 g) and 47.04 kHz (the fluorine nuclei Larmor frequency). The oscillations occur in a tuned circuit which resonates at the two frequencies. The frequency stability as a function of averaging time of the maser was measured by a period counting technique which uses one oscillation frequency as a clock against which the other oscillation frequency is determined. This method is shown to yield (in principle) the stability that would be directly measured (using a perfect clock) for the maser operating in an absolutely constant magnetic field.