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Resonant noninear refraction of 4-5 $\mu$m light in CO and CO$_2$ gas
preprintposted on 2023-01-11, 23:05 authored by Jeremy Pigeon, Dana Tovey, Sergei Tochitsky, Gerhardus Louwrens, Ilan Ben-Zvi, Dmitry Martyshkin, Vladimir Fedorov, Krishna Karki, Sergey Mirov, Chan Joshi
The resonant nonlinear refraction of 4-5 $\mu$m light in CO and CO$_2$ gas at a peak intensity of 15 MW/cm$^2$ was demonstrated using time- and frequency-resolved measurements of self-focusing and self-defocusing. The nonlinearity of these molecular gases exhibits intensity-dependent sign reversals and a < 4 ns response time. A change from self-focusing to self-defocusing or vice-versa was observed to occur for Rabi frequencies that are comparable to the collisional linewidth. A density matrix model for the nonlinear susceptibility of a strongly driven two-level system provides a qualitative explanation for these results.