Observation of coherent transients in ultrashort chirped excitation of an undamped two-level system

The effects of Coherent excitation of a two level system with a linearly chirped pulse are studied theoretically and experimentally (in Rb (5s - 5p)) in the low field regime. The Coherent Transients are measured directly on the excited state population on an ultrashort time scale. A sharp step corresponds to the passage through resonance. It is followed by oscillations resulting from interferences between off-resonant and resonant contributions. We finally show the equivalence between this experiment and Fresnel diffraction by a sharp edge.Comment: 4 pages, 4 figures, to appear in PR

Exchange of Photons between Two Atoms in a 1D Waveguide. Gauge Dependent and Independent Couplings

Two atoms located in a one dimensional waveguide with initially one of them in the excited state interact by exchanging photons. We analyze the exchange process distinguishing between real and virtual photons contributions, and comparing between the Coulomb and Goeppert-Mayer gauges. We show that gauge-independent coupling terms can be interpreted in a simple way using the time-energy incertitude relatio

First plasma and tissue pharmacikinetic study of the YSNSG cyclopeptide, a new integrin antagonist, using microdialysis.

International audienc

Temporal coherent control induced by wave packet interferences in one and two photon atomic transitions

International audienceThe interaction of a sequence of two identical ultrashort laser pulses with an atomic system results in quantum interferences as in Ramsey fringes experiments. These interferences allow achievement of temporal coherent control of the excitation probability. We present the results of a temporal coherent control experiment on two different atomic systems: one-photon absorption in K (4s-4p) and two-photon absorption in Cs (6s-7d). In K, the quantum interferences between the two excitation paths associated with the laser pulses are revealed through rapid oscillations of the excitation probability as a function of the time delay between the two pulses. These oscillations take place at the transition frequency (period T = 2.56 fs). The interferences are modulated by beats (at about 580 fs) resulting from the doublet structure of the excited state (4p (P-2(1/2), P-2(3/2))). Three complementary interpretations of this experiment are presented: in terms of beats of quantum interferences, of variation in the spectrum intensity, and of wave packet interferences. Whenever the two laser pulses are temporally overlapped, optical interferences are superimposed on to the quantum interferences. The distinction between these two types of interference lis clearly revealed in the two-photon excitation scheme performed on Cs (6s-7d (D-2(3/2), D-2(5/2))) because quantum interferences occur at twice the frequency of the optical interferences

Propagation of ultra-short pulses in resonant atomic systems : Observation and control

We discuss the possibility to control through two different experiments, the propagation effects that occur when an optically dense atomic medium is excited by ultra-short laser pulses. In the first experiment a direct compensation of the dispersion for one single pulse is obtained with a pulse-shaper device. In the second experiment, ce of ultra-short laser pulses is used. The dispersion effects are shown to depend crucially on the relative phase between the pulses