Theory of two-photon absorption and emission second-order saturation effect

清 西川, 昭 佐道, Hiroshi Sekiya +3 more

Pietro Bucci, Massimo Martinelli, S. Santucci

A general theory has been developed to calculate the response, in NMR conditions, of a spin system irradiated by two nearly resonant waves having different frequencies and intense enough to produce an appreciable saturation. The absorption signal has been calculated employing the statistical operator technique, treating the electromagnetic field by the second quantization formalism. Two kinds of transitions are expected: The first one arises from processes in which n photons of one wave are emitted and n photons of the other wave are absorbed, the second one arises from processes involving the emission of n photons of one wave and the absorption of n ± 1 photons of the other. In the first case all the transitions coalesce in a single dispersionlike signal, which occurs when the frequencies of the two waves are nearly the same; in the second case a many-line spectrum occurs in which emission and absorption lines are present. The experimental results here reported strictly agree with theoretical previsions.

Tse-Min Chiang, George Chappell Schatz

This paper presents a comprehensive study of the theory of entangled two-photon emission/absorption (E2P-EA) between a many-level cascade donor and a many-level acceptor (which could be quantum dots or molecules) using second-order perturbation theory and where the donor-acceptor pair is in a homogeneous but dispersive medium. To understand the mechanism of E2P-EA, we analyze how dipole orientation, radiative lifetime, energy detuning between intermediate states, separation distance, and entanglement time impact the E2P-EA rate. Our study shows that there are quantum interference effects in the E2P-EA rate expression that lead to oscillations in the rate as a function of entanglement time. Furthermore, we find that the E2P-EA rate for a representative system consisting of two quantum dots can be comparable to one-photon emission/absorption (OP-EA) when donor and acceptor are within a few nm. However, the E2P-EA rate falls off much more quickly with separation distance than does OP-EA.

Hiroshi Sekiya, Seikyo Tsunekawa, Kiyoshi Nishikawa +1 more

C. Bendjaballah, Guy Oliver

Two models of saturated coherent light amplifier are studied and compared from the statistical point of view. For one of the models the absorption process is not saturated. The first- and second-order moments of the photon distribution exhibit very different behaviors according to the considered model. The reduced second-order moment measuring the fluctuations becomes more important when the absorption process is not saturated.

Sunil Kumar