Extremely nonlinear Raman interaction of an ultrashort nitrogen ion laser with an impulsively excited molecular wave packet
Zhaoxiang Liu, Jinping Yao, Haisu Zhang, Bo Xu, Jinming Chen, Fangbo Zhang, Zhihao Zhang, Yuexin Wan, Wei Chu, Zhenhua Wang, Ya Cheng
Abstract
We report on the generation of cascaded rotational Raman scattering up to 58th order in coherently excited $\mathrm{C}{\mathrm{O}}_{2}$ molecules. Raman scattering with more than 600 sidebands is obtained using an intense femtosecond laser to impulsively excite rotational coherence and femtosecond-laser-induced ${{\mathrm{N}}_{2}}^{+}$ lasing to generate cascaded Raman signals. This configuration allows this experiment to be performed with a single femtosecond laser beam at free-space standoff locations. It is revealed that the efficient spectral extension of Raman signals is attributed to the specific structures of ${{\mathrm{N}}_{2}}^{+}$ lasing in the spectral and temporal domains and the ideal spatial overlap of the femtosecond laser and ${{\mathrm{N}}_{2}}^{+}$ lasing. A Raman spectrum extending above $2000\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ naturally corresponds to a femtosecond pulse train due to the periodic revivals of molecular rotational wave packets.