Extremely nonlinear Raman interaction of an ultrashort nitrogen ion laser with an impulsively excited molecular wave packet

We report on the generation of cascaded rotational Raman scattering up to 58th order in coherently excited CO2 molecules. Raman scattering with more than 600 sidebands is obtained using an intense femtosecond laser to impulsively excite rotational coherence and femtosecond-laser-induced N2+ 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 N2+ lasing in the spectral and temporal domains and the ideal spatial overlap of the femtosecond laser and N2+ lasing. A Raman spectrum extending above 2000cm-1 naturally corresponds to a femtosecond pulse train due to the periodic revivals of molecular rotational wave packets.