15 research outputs found
Localized Emitting State and Energy Transfer Properties of Quadrupolar Chromophores and (Multi)Branched Derivatives
Femtosecond laser pulse train effect on Doppler profile of cesium resonance lines
We present direct observation of the velocity-selective optical pumping of
the Cs ground state hyperfine levels induced by the femtosecond (fs) laser
oscillator centered at either D2 (6 2S1/2↦6 2P3/2,
852 nm) or D1 (6 2S1/2↦6 2P1/2, 894 nm) cesium
line. We utilized previously developed modified direct frequency comb
spectroscopy (DFCS) which uses a fixed frequency comb for the excitation and
a weak cw scanning probe laser centered at the 133Cs 6
2S1/2↦6 2P3/2 transition (D2 line) for ground
levels population monitoring. The frequency comb excitation changes the
usual Doppler absorption profile into a specific periodic, comblike
structure. The mechanism of the velocity selective population transfer
between the Cs ground state hyperfine levels induced by fs pulse train
excitation is verified in a theoretical treatment of the multilevel atomic
system subjected to a pulse train resonant field interaction
Static and dynamic properties of low-temperature order in the one-dimensional semiconductor (NbSe<sub>4</sub>)<sub>3</sub>I
International audienceWe investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor (NbSe 4) 3 I by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a welldocumented pseudo-Jahn-Teller ferrodistortive structural transition at T C = 274 K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at T * ≈ 160 K. Although antiferroelectric (AFE) phase is partially formed at T C , our results consistently point to an enhancement of the interchain order at T * , thus leading to AFE order-disorder transition, as supported by the earlier dielectric and structural studies