Frontiers in Optics

Pulse Width Effect on Rb2 Predissociation by Negatively Chirped Femtosecond Laser Pulses

Y. Xiao, Ju Gao, James Gary Eden

Published Jan 1, 2006• 0 citations

Abstract

The effect of laser pulse width on Rb2 predissociation is probed. The relative yields of Rb excited state fragments with different pulse widths are compared experimentally. Reproducible dissociation channels are observed.

DOI: 10.1364/fio.2006.jwd125

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Frontiers in Optics

Pulse Width Effect on Rb2 Predissociation by Negatively Chirped Femtosecond Laser Pulses

Y. Xiao, Ju Gao, James Gary Eden

Published Jan 1, 2006• 0 citations

Publisher

Abstract

DOI: 10.1364/fio.2006.jwd125

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Conference on Lasers and Electro-OpticsMay 1, 20070 citations

Effects of chirping on the dissociation dynamics of H 2 in a two-frequency laser field

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Propagation of optical pulses in a resonantly absorbing medium: Observation of negative velocity in Rb vapor

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Propagation of optical pulses in a resonantly absorbing medium is studied. Propagation time of nanosecond pulses was measured for the Rb ${D}_{1}$ transition. At the center of two absorption lines, delay of the pulse peak which is about ten times as large as the pulse width was observed, where zero delay is defined for the propagation with the light velocity in vacuum. On the other hand, at the peak of an absorption line, negative delay was observed for large absorption, where the advance time is as large as 25% of the pulse width. Simulation including the effect of absorption and phase shift reproduced well the experimental results.Propagation of optical pulses in a resonantly absorbing medium is studied. Propagation time of nanosecond pulses was measured for the Rb ${D}_{1}$ transition. At the center of two absorption lines, delay of the pulse peak which is about ten times as large as the pulse width was observed, where zero delay is defined for the propagation with the light velocity in vacuum. On the other hand, at the peak of an absorption line, negative delay was observed for large absorption, where the advance time is as large as 25% of the pulse width. Simulation including the effect of absorption and phase shift reproduced well the experimental results.

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We present the effects of frequency chirping of laser pulses on (1+1)-photon resonance-enhanced dissociation dynamics of

{\mathrm{H}}_{2}.

The dissociation occurs via two closely spaced nonadiabatically coupled intermediate levels which are in one-photon resonance or near resonance with the initial level. Predissociating levels embedded into continua are considered. When the first laser field is sufficiently intense and suitably chirped, the dissociation probability is enhanced by adiabatic rapid passage through the avoided crossing arising from the frequency swept radiative interaction. The whole population of the ground level can be effectively transferred to the intermediate levels by this technique facilitating the dissociation process by the second field. We also report the effect of frequency detuning and chirp width on the dissociation probability. Widths of the two peaks of the dissociation line shape increase with an increase in chirp width, resulting in the possibility of control in the dissociation yield. When the first field is a laser pulse of low intensity and constant frequency and the second laser frequency is chirped, predissociating levels take important parts in the dissociation dynamics and we obtain a signature of the nonadiabatic effect of the first step on the second step of photodissociation dynamics. This feature is due to the presence of the predissociating levels and the nonadiabatic mixing of two intermediate levels. All these results can be explained in terms of the adiabatic dressed levels.

Propagation of optical pulses in a resonantly absorbing medium is studied. Propagation time of nanosecond pulses was measured for the Rb

{D}_{1}

transition. At the center of two absorption lines, delay of the pulse peak which is about ten times as large as the pulse width was observed, where zero delay is defined for the propagation with the light velocity in vacuum. On the other hand, at the peak of an absorption line, negative delay was observed for large absorption, where the advance time is as large as 25% of the pulse width. Simulation including the effect of absorption and phase shift reproduced well the experimental results.