We use a semlclassical, effective-state approach to laser pulse propagation in a gas of polyatomic molecules. Our numerical model of multiple-photon excitation includes quasicontinuum transitions to calculate the effects of coherent propagation on multiple- photon absorption. The molecular model consists of a single ground state and several bands of discrete states, which are successively connected by means of electric-dipole transitions.1 This model correctly simulates some of the major characteristics of multiple- photon absorption, such as power threshold, fluence-dependent absorption, and complete population inversion at large fluences. As the pulse propagates, the Rabi oscillations induced in the lower-level states are encoded onto the pulse and create a series of peaks and troughs similar to those found in pulse propagation in two-level systems.2 Another coherent propagation effect that can change the excitation process is coherent sideband generation. Temporal distortions and the generation of new frequencies result in changes in the population distribution among the states, as well as changes in the total population transferred to the quasicontinuum. The effective increase in total population transfer by propagation effects is offset by the decrease in fluence. The resulting transfer of energy from the pulse to the molecule depends strongly on the initial characteristics of the pulse.We use a semlclassical, effective-state approach to laser pulse propagation in a gas of polyatomic molecules. Our numerical model of multiple-photon excitation includes quasicontinuum transitions to calculate the effects of coherent propagation on multiple- photon absorption. The molecular model consists of a single ground state and several bands of discrete states, which are successively connected by means of electric-dipole transitions.1 This model correctly simulates some of the major characteristics of multiple- photon absorption, such as power threshold, fluence-dependent absorption, and complete population inversion at large fluences. As the pulse propagates, the Rabi oscillations induced in the lower-level states are encoded onto the pulse and create a series of peaks and troughs similar to those found in pulse propagation in two-level systems.2 Another coherent propagation effect that can change the excitation process is coherent sideband generation. Temporal distortions and the generation of new frequencies result in changes in the population distribution among the states, as well as changes in the total population transferred to the quasicontinuum. The effective increase in total population transfer by propagation effects is offset by the decrease in fluence. The resulting transfer of energy from the pulse to the molecule depends strongly on the initial characteristics of the pulse.

Annual Meeting Optical Society of AmericaJan 1, 19900 citations

Coherent Spontaneous Emission of Multilevel Systems

Махвиладзе Тариэль Михайлович, Leonid A. Shelepin

Journal of Experimental and Theoretical PhysicsJan 1, 19720 citations

Vibrational molecular modulation in hydrogen

Shu Wei Huang, Wei-Jan Chen, A. H. Kung

Detailed numerical modeling of using the vibrational coherence of ${\mathrm{H}}_{2}$ for molecular modulation is presented. The focus of the calculation is on a strongly driven system aimed at producing many sidebands in the presence of Doppler broadening and the effects of collisions at room temperature. It is shown that Dicke narrowing that reduces the Doppler width plays a critical role in high order sideband generation in room temperature ${\mathrm{H}}_{2}$ . In addition, the calculation shows that generation of many sidebands favors the phased state as has been reported in all gas phase experiments and is primarily a consequence of the Stark shifts that result from the applied high intensities. The influence of self-focusing in the gas medium that has been conjectured in previous studies is only secondary. The numerical results agree with experimental data obtained in our laboratory, where we have succeeded in generating collinearly propagating Raman sidebands with wavelengths that range from $2216\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the infrared to $133\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the vacuum ultraviolet. The frequencies covered by these sidebands span over four octaves for a total of more than $70\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in the optical region of the spectrum.Detailed numerical modeling of using the vibrational coherence of ${\mathrm{H}}_{2}$ for molecular modulation is presented. The focus of the calculation is on a strongly driven system aimed at producing many sidebands in the presence of Doppler broadening and the effects of collisions at room temperature. It is shown that Dicke narrowing that reduces the Doppler width plays a critical role in high order sideband generation in room temperature ${\mathrm{H}}_{2}$. In addition, the calculation shows that generation of many sidebands favors the phased state as has been reported in all gas phase experiments and is primarily a consequence of the Stark shifts that result from the applied high intensities. The influence of self-focusing in the gas medium that has been conjectured in previous studies is only secondary. The numerical results agree with experimental data obtained in our laboratory, where we have succeeded in generating collinearly propagating Raman sidebands with wavelengths that range from $2216\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the infrared to $133\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the vacuum ultraviolet. The frequencies covered by these sidebands span over four octaves for a total of more than $70\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in the optical region of the spectrum.

Physical Review ADec 26, 200617 citations

Laser propagation effects in multilevel systems (A)

Cyrus D. Cantrell, Gary L. Peterson, David R. Adams +2 more

Journal of the Optical Society of America ADec 1, 19810 citations

Detailed numerical modeling of using the vibrational coherence of

{\mathrm{H}}_{2}

for molecular modulation is presented. The focus of the calculation is on a strongly driven system aimed at producing many sidebands in the presence of Doppler broadening and the effects of collisions at room temperature. It is shown that Dicke narrowing that reduces the Doppler width plays a critical role in high order sideband generation in room temperature

{\mathrm{H}}_{2}

. In addition, the calculation shows that generation of many sidebands favors the phased state as has been reported in all gas phase experiments and is primarily a consequence of the Stark shifts that result from the applied high intensities. The influence of self-focusing in the gas medium that has been conjectured in previous studies is only secondary. The numerical results agree with experimental data obtained in our laboratory, where we have succeeded in generating collinearly propagating Raman sidebands with wavelengths that range from

2216\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

in the infrared to

133\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

in the vacuum ultraviolet. The frequencies covered by these sidebands span over four octaves for a total of more than $70\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in the optical region of the spectrum.