Nonresonance absorption of an energy quantum by a two-level atom

S. A. Moiseev, E. I. Shtyrkov

S. A. Moiseev, M. I. Noskov

Baihong Li, Yonggang Xu, Lan An +4 more

We theoretically investigate the nonresonant two-photon absorption (TPA) process in a two-level atom induced by a weak chirped pulse in the frequency domain. According to the extremum condition of the two-photon transition probability (TPTP) at the transition center frequency, we propose a Fresnel-inspired pulse tailoring scheme for TPA that is significantly different from that of Broers et al. [Phys. Rev. A46, 2749 (1992)]. Using this scheme, the TPTP can be focused or eliminated completely by constructively or destructively modulating various pathways of the quantum interference. Our results are a significant improvement on those obtained by Broers et al. and will have potential applications in selective two-photon microscopy and spectroscopy.

Baihong Li, Huafeng Pang, Doudou Wang +3 more

Abstract In this study, the nonresonant two-photon absorption process in a two-level atom, induced by a weak chirped pulse, is theoretically investigated in the frequency domain. An analytical expression of the wave function expressed by Fresnel functions is obtained, and the two-photon transition probability (TPTP) versus the integral bandwidth, spectral width, and chirp parameter is analyzed. The results indicate that the oscillation evolution of the TPTP result from quantum diffraction of the wave function, which can be explained by analogy with Fresnel diffraction from a wide slit in the spatial domain. Moreover, the ratio between the real and imaginary parts of the excited state wave function and, hence, the atomic polarization, can be controlled by the initial phase of the excitation pulse. In some special initial phase of the excitation pulse, the wave functions with purely real or imaginary parts can be obtained by measuring the population probability. This work provides a novel perspective for understanding the physical details of the interactions between atoms and chirped light pulses in the multiphoton process.

Masataka Mizushima

When a radiation field of frequency ω1 interacts with atoms, etch of which has a transition frequency ω b a =(E b -E a )/\hbar, with ω1-ω b a =Δ≠0, nonresonant absorption can take place with probability P 1 inversely proportional to Δ 2 (a pressure broadening). When another radiation field of frequency ω2, such that ω1+ω2=2 ω b a , interacts simultaneously with the gas a resonant two-photon absorption can take place in addition to the nonresonant absorption. The probability of this two-photon absorption process, P 2, is found to be inversely proportional to Δ 4. If \varOmega=| <n-1|E|n ><b| µ|a >| is the Rabi frequency of the transition, it is found that P 2/(P 1(Δ)+P 1(-Δ)) is given by 12{ \varOmega(-Δ)\varOmega(-Δ)}2/{Δ 2(\varOmega(-Δ)2+\varOmega(Δ)2)}.

Richard M. Friedberg, Sven R. Hartmann, Jamal T. Manassah