Detection of Spin Magnetization Variation in a Two-level Maser Oscillator

Abstract

THE phenomenon of amplitude modulation in the spontaneous emission of two-level masers has been observed by several investigators^1–3, and has been the subject of a number of theoretical discussions^3–5. The basic mechanism underlying most of the semi-classical treatments is an oscillatory transfer of energy between the spin system, in the working substance, and the cavity radiation field. In such a process the spin magnetization vector M should undergo damped, pendulum-like nutations, correlated to the modulation of the emission, between the inverted state, M anti-parallel to the steady magnetic field in the z direction, and the thermal equilibrium state, M parallel to the steady field. The quantum mechanical treatment⁶ of the interaction between the spin system and the radiation field in the cavity also suggests the oscillatory behaviour of M_z. Stevens⁶ further suggested that the direct observation of the variation of M_z, during an oscillation pulse, would be a more instructive test of the theories mentioned than monitoring the modulated cavity energy. Evidence confirming the suggested behaviour of M has been obtained in an induction experiment designed to detect the variations in the ‘dipole’ field of M_z.