Two-Photon Coherent Atomic Absorption of Multiple Laser Beams

M Patel, Gerhard De Jager, Z Nkosi +2 more

In this paper we report on the study of two and multi-level atoms interacting with multiple laser beams. The semi-classical approach is used to describe the system in which the atoms are treated quantum mechanically via the density matrix operator, while the laser beams are treated classically using Maxwells equations. We present results of a two level atom interacting with single and multiple laser beams and demonstrate Rabi oscillations between the levels. The effects of laser modulation on the dynamics of the atom (atomic populations and coherences) are examined by solving the optical Bloch equations. Plots of the density matrix elements as a function of time are presented for various parameters such as laser intensity, detuning, modulation etc. In addition, phase-space plots and Fourier analysis of the density matrix elements are provided. The atomic polarization, estimated from the coherence terms of the density matrix elements, is used in the numerical solution of Maxwells equations to determine the behaviour of the laser beams as they propagate through the atomic ensemble. The effects of saturation and hole-burning are demonstrated in the case of two counter propagating beams with one being a strong beam and the other being very weak. The above work is extended to include four-wave mixing in four level atoms in a diamond configuration. Two co-propagating beams of different wavelengths drive the atoms from a ground state |1〉 to an excited state |3〉 via an intermediate state |2〉. The atoms then move back to the ground state via another intermediate state |4〉, resulting in the generation of two additional correlated photon beams. The characteristics of these additional photons are studied.

Ming Chiayg Li

NILOY KUMAR DUTTA

Ming Chiang Li

Proposed and performed experiments on the Doppler-free two-photon absorption of two coherent laser beams are discussed. The coherent phenomenon in experiments follows directly from basic quantum mechanics. It is shown that, to excite the coherent absorption, the laser beams need not be spatially or temporally separated.

Ming-Chiang Li

Jun Ishikawa, F. Riehle, J. Helmcke +1 more

We have investigated both theoretically and experimentally saturated absorption of a long-lifetime transition in a calcium atomic beam excited either by a standing wave or by two counterpropagating traveling waves. For standing-wave excitation the usual saturation dip is turned into a peak and then evolves into a triplet as the laser intensity is increased. A theoretical framework has been developed to account for the interaction of atoms with multiple-wave excitation based on a combination of free propagators and S matrices, also applicable to atomic interferometry. The shapes of the wave packets prepared by optical beam splitters are derived. The experimental size and shape of the absorption signal are reproduced by theory only when the actual laser profile is accurately represented and if the recoil physics is introduced because of multiple momentum exchanges between atoms and light in strong laser fields.