Search results for "42.50.Md"
showing 4 items of 4 documents
Field-free molecular alignment for probing collisional relaxation dynamics
2013
International audience; We report the experimental study of field-free molecular alignment in CO2 gas mixtures induced by intense femtosecond laser pulses in the presence of collisional processes. We demonstrate that the alignment signals exhibit specific features due to nontrivial collisional propensity rules that tend to preserve the orientation of the rotational angular momentum of the molecules. The analysis is performed with a quantum approach based on the modeling of rotational J- and M-dependent state-to-state transfer rates. The present work paves the way for strong-field spectroscopy of collisional dynamics.
Probing ultrafast thermalization with field-free molecular alignment
2012
International audience; The rotation-translation thermalization of CO2 gas is investigated 500 ps after its preheating by a nonresonant short and intense laser pulse. The temperature of thermalization is optically determined with two additional short laser pulses enabling a field-free molecular alignment process and its probing, respectively. The measurements are performed for various intensities of the preheat pulse, leading to the observation of different temperatures which are in very good agreement with classical molecular dynamics simulations. The results can be regarded as a step towards real-time tracking of ultrafast relaxation pathways in molecular motion.
High rate concentration measurement of molecular gas mixtures using a spatial detection technique
2010
International audience; Concentration measurement in molecular gas mixtures using a snapshot spatial imaging technique is reported. The approach consists of measuring the birefringence of the molecular sample when field-free alignment takes place, each molecular component producing a signal with an amplitude depending on the molecular density. The concentration measurement is obtained on a single-shot basis by probing the time-varying birefringence through femtosecond time-resolved optical polarigraphy (FTOP). The relevance of the method is assessed in air.
Narrow and contrast resonance of increased absorption in Λ-system observed in Rb cell with buffer gas
2009
International audience; We report observation of a narrow (sub-natural) and high-contrast resonance of increased absorption (“bright” resonance) in Rb cell with Ne buffer gas under previously unexplored experimental conditions for coupling and probe radiation configuration. The coupling laser-stabilized frequency is detuned by ~3 GHz from 5S1/2, Fg=3 → 5P3/2, Fe=2,3,4 transitions, while the probe laser frequency is scanned across these transitions. We believe the bright resonance formation, occurring when the probe laser frequency is blue-shifted from the coupling frequency by a value of the ground state hyperfine splitting, is caused predominantly by a 2-photon absorption of the probe radi…