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Журнал Экспериментальной и Теоретической Физики

Second-order processes with respect to a weak radiation field on a 'dressed' atom

G. Yu. Kryuchkov, Vanik E. Mkrtchian, M. L. Ter-Mikaelian, V. O. Chaltykyan

Published Jan 1, 1985• 0 citations
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`Dressed' atom radiation processes which are first order in the weak field

M.L. Ter-Mikayelyan

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Giant second-order cross nonlinearities via direct perturbation to the dark state in coherent population trapping

Guanghui Wang, Xiangming Hu, Qingping Hu +1 more

We study the nonlinearities due to direct perturbation to the dark state in coherent population trapping (CPT). To extract the susceptibilities of the CPT atoms with respect to probe fields, we treat the CPT dressing fields as control parameters and redefine susceptibilities with respect to the probe fields alone. With such a redefinition, we reveal that a CPT-based system displays an ultralarge, resonantly enhanced second-order cross susceptibility ${\ensuremath{\chi}}^{(2)}$ together with vanishing linear absorption. Physically, this effect is based on the CPT dark-state shift, which is traced to the six-photon parametric processes for all involved fields (including the dressing and probe fields). Because of the lack of the direct perturbation, this effect is absent in the electromagnetically induced transparency (EIT)-based system, in which only resonantly enhanced third-order (Kerr) susceptibility ${\ensuremath{\chi}}^{(3)}$ is obtainable but much weaker than the second-order one. The second-order nonlinearity, because of its stronger effect, can be more sensitive for quantum nonlinear optics at low light levels than the third-order nonlinearity.

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Higher order adiabatic separation of strongly coupled systems. I. Two-body systems and dressed hydrogen atom

T. T. Nguyen‐Dang, André D. Bandrauk

The phase corrected adiabatic separation method proposed recently by Marechal [J. Chem. Phys. 83, 247 (1985)] is reexamined. We have been able to show that a state independent differential equation exists, which governs the phase coupling function f of this method, if f further satisfies a set of constraints, Eqs. (7) of the present paper. The method is illustrated by its application to three simple, exactly soluble two-body systems: the free hydrogen atom, the linearly forced hydrogen atom, and the system of two harmonically coupled oscillators. We show that for these systems, the present method, which employs an adiabatic separation procedure, after phase correcting the Hamiltonian, leads to exact results, suggesting its utility for more general problem, involving nonseparable potentials. A nonseparable system of particular interest is the dressed hydrogen atom, which is a representative of all dressed systems, molecular or atomic, with respect to radiative couplings. The method of phase corrected adiabatic separation is shown to give, for field frequencies lying below an IR threshold, a better representation for the exact eigenstates of this dressed systems, as ensuing residual couplings are estimated to be of second order in the original radiative coupling constant.

The Journal of Chemical Physics•Dec 15, 1986•8 citations

Probe absorption spectrum of a laser-driven atom near a phase conjugator

Henk F. Arnoldus, Thomas F. George

The absorption spectrum for weak radiation of a two-state atom near the surface of a phase-conjugating four-wave mixer has been evaluated. Also included is the option that the atom is illuminated by a near-resonant laser field. In the secular limit with respect to the laser-dressed atomic states the absorption spectrum has two lines, just as for a free atom. The strengths and the widths of these lines depend on the phase-conjugate reflectivity, as well as on the optical parameters. It is shown that increasing the reflectivity drives the atom towards saturation through three-photon processes. Also the driving laser tends to saturate the transition, but it is shown that both mechanisms have a different effect on the absorption profile, and can hence be distinguished experimentally.

Physical Review A•Nov 1, 1993•3 citations
We study the nonlinearities due to direct perturbation to the dark state in coherent population trapping (CPT). To extract the susceptibilities of the CPT atoms with respect to probe fields, we treat the CPT dressing fields as control parameters and redefine susceptibilities with respect to the probe fields alone. With such a redefinition, we reveal that a CPT-based system displays an ultralarge, resonantly enhanced second-order cross susceptibility ${\ensuremath{\chi}}^{(2)}$ together with vanishing linear absorption. Physically, this effect is based on the CPT dark-state shift, which is traced to the six-photon parametric processes for all involved fields (including the dressing and probe fields). Because of the lack of the direct perturbation, this effect is absent in the electromagnetically induced transparency (EIT)-based system, in which only resonantly enhanced third-order (Kerr) susceptibility ${\ensuremath{\chi}}^{(3)}$ is obtainable but much weaker than the second-order one. The second-order nonlinearity, because of its stronger effect, can be more sensitive for quantum nonlinear optics at low light levels than the third-order nonlinearity.
The phase corrected adiabatic separation method proposed recently by Marechal [J. Chem. Phys. 83, 247 (1985)] is reexamined. We have been able to show that a state independent differential equation exists, which governs the phase coupling function f of this method, if f further satisfies a set of constraints, Eqs. (7) of the present paper. The method is illustrated by its application to three simple, exactly soluble two-body systems: the free hydrogen atom, the linearly forced hydrogen atom, and the system of two harmonically coupled oscillators. We show that for these systems, the present method, which employs an adiabatic separation procedure, after phase correcting the Hamiltonian, leads to exact results, suggesting its utility for more general problem, involving nonseparable potentials. A nonseparable system of particular interest is the dressed hydrogen atom, which is a representative of all dressed systems, molecular or atomic, with respect to radiative couplings. The method of phase corrected adiabatic separation is shown to give, for field frequencies lying below an IR threshold, a better representation for the exact eigenstates of this dressed systems, as ensuing residual couplings are estimated to be of second order in the original radiative coupling constant.
The absorption spectrum for weak radiation of a two-state atom near the surface of a phase-conjugating four-wave mixer has been evaluated. Also included is the option that the atom is illuminated by a near-resonant laser field. In the secular limit with respect to the laser-dressed atomic states the absorption spectrum has two lines, just as for a free atom. The strengths and the widths of these lines depend on the phase-conjugate reflectivity, as well as on the optical parameters. It is shown that increasing the reflectivity drives the atom towards saturation through three-photon processes. Also the driving laser tends to saturate the transition, but it is shown that both mechanisms have a different effect on the absorption profile, and can hence be distinguished experimentally.