Two-level system in a resonant multifrequency field

M. D. Anosov

Gadi Goelman, David B. Zax, Shimon Vega

Experimentally achievable conditions where only weak off-resonant fields are used to excite coherence in a two-level system are explored. A brief review of previous theoretical results useful in treating multifrequency irradiation sequences is provided. Using an approximation method based on the Floquet formalism we derive an expression for the effective field strength as a function of the phases and amplitudes of the applied irradiation fields. Some of these results are rederived and/or explained in a simplified manner. Under conditions of four-frequency irradiation, three-photon excitation of a two-level system in NMR is experimentally demonstrated on the spin-1/2 system of the 31P nucleus in phosphoric acid. The behavior of the three-photon resonance is explored as a function of all important experimental parameters. The results of these tests conform closely to the theoretical predictions. Possible uses of multifrequency irradiation schemes in NMR are suggested.

Namita Gupta

N. E. Nevesskiǐ

Yevgeny V. Radeonychev

Generation of coherent multifrequency optical radiation by means of excitation of mechanical vibration (acoustical oscillation) of a medium along the propagation of resonant laser radiation is proposed. At the same time the vibrating medium becomes transparent for the incident resonant radiation (acoustically induced transparency). We show, that generation of multifrequency radiation takes place in the absence of inversion in two-level quantum system for any energy distribution among the spectral components of the incident (multifrequency in general) field and any amplitude of vibration. Amplitude of vibration determines efficiency of the normal wave generation. Mechanism of the effect is destructive interference of different spectral harmonics of the field components appearing in the frame of vibrating atoms.

Z. K. Yankauskas, G. I. Valyukenas