Paper 1.6: "Resonance Transitions Induced by Perturbations at Two or More Different Frequencies," N. F. Ramsey, Phys. Rev. 100, 1191–1194 (1955)
Reprinted with permission from The Physical Review. Copyright 1955, The American Physical Society.
This theoretical paper initially arose from my worry that irregularities of the static magnetic field between the two separated oscillatory field regions might shift the resonance frequency. I realized I could calculate a special case of the effect by noting that the passage of the molecule over the irregularities would be similar to the effect of an oscillatory field in the intermediate region. In other words the molecule would be subject to two oscillatory fields at different frequencies: one in the two end fields inducing the transitions and one in the intermediate region that might pull the resonance frequency. I show in the paper that such pulling does occur and that it does so not only with separated oscillatory fields but also with Rabi's single oscillatory field method. I also note that there are many ways in which there can be additional oscillatory fields, including their deliberate application or their use in another resonance experiment at the same time. After solving the general problem of an additional rotating field, I realized that F. Bloch and A. Siegert had earlier solved a special case.
An experimental confirmation of the frequency pulling by another oscillatory magnetic field is reported by H. R. Lewis, A. Pery, W. Quinn and N. F. Ramsey in Phys. Rev. 107, 446–449 (1957).
