Letter | Published:

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

Naturevolume 192pages860861 (1961) | Download Citation



THE phenomenon of amplitude modulation in the spontaneous emission of two-level masers has been observed by several investigators1–3, and has been the subject of a number of theoretical discussions3–5. 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 Mz. Stevens6 further suggested that the direct observation of the variation of Mz, 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 Mz.

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  1. 1

    Feher, G., Gordon, J. P., Buehler, E., Gere, E. A., and Thormund, C. D., Phys. Rev., 109, 221 (1958).

  2. 2

    Chester, P. F., Wagner, P. E., and Castle, jun., J. G., Phys. Rev., 110, 281 (1958).

  3. 3

    Kemp, J. C., J. App. Phys., 30, 1451 (1959).

  4. 4

    Wang, S., and Singer, J. R., J. App. Phys., 32, 1371 (1961).

  5. 5

    Yariv, A., J. App. Phys., 31, 740 (1960).

  6. 6

    Stevens, K. W. H., and Josephson, jun., B., Proc. Phys. Soc., 74, 561 (1959).

  7. 7

    Campbell, C. K., and Bijl, D. (to be published).

  8. 8

    Firth, I. M. (to be published).

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  1. School of Natural Philosophy, University of St. Andrews

    • I. M. FIRTH
    •  & D. BIJL


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