Vibrational molecular modulation in hydrogen

Abstract

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.