Multiphoton Transitions in a Spin System Driven by Strong Bichromatic Field

Saiko, A. P.; Fedoruk, G. G.; Markevich, S. A.

Multiphoton Transitions in a Spin System Driven by Strong Bichromatic Field

Authors

Saiko, A. P.

Fedoruk, G. G.

Markevich, S. A.

Description

EPR transient nutation spectroscopy is used to measure the effective field (Rabi frequency) for multiphoton transitions in a two-level spin system bichromatically driven by a transverse microwave (MW) field and a longitudinal radio-frequency (RF) field. The behavior of the effective field amplitude is examined in the case of a relatively strong MW field, when the derivation of the effective Hamiltonian cannot be reduced to first-order perturbation theory in w_{1} / w_{rf} (w_{1} is the microwave Rabi frequency, w_{rf} is the RF frequency). Experimental results are consistently interpreted by taking into account the contributions of second and third order in w_{1} / w_{rf} evaluated by Krylov-Bogolyubov-Mitropolsky averaging. In the case of inhomogeneously broadened EPR line, the third-order correction modifies the nutation frequency, while the second-order correction gives rise to a change in the nutation amplitude due to a Bloch-Siegert shift.
7 pages, 6 figures