Two-photon excitation in nuclear magnetic and quadrupole resonance

摘要

NMR and NQR experiments are almost always performed by exciting the allowed transitions of nuclear spins with on- or near-resonant magnetic fields. An under-appreciated fact however is that resonant fields are not required. In fact early in Abragam’s classic text [1] it is shown that excitation of NMR signals may be carried out with irradiation at 1/3 of the resonance frequency. Coherent excitation is possible with any combination of oscillating fields for which a sum of integer multiples of the applied fields’ frequencies is sufficiently close to resonance.