  We report generation of cascaded rotational Raman scattering up to 58th
orders in coherently excited CO_2 molecules. The high-order Raman scattering,
which produces a quasiperiodic frequency comb with more than 600 sidebands, is
obtained using an intense femtosecond laser to impulsively excite rotational
coherence and the femtosecond-laser-induced N_2^+ lasing to generate cascaded
Raman signals. The novel 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 spectra-temporal structures of N_2^+ lasing, the ideal spatial
overlap of femtosecond laser and N2+ lasing, and the guiding effect of
molecular alignment. The Raman spectrum extending above 2000 cm^-1 naturally
corresponds to a femtosecond pulse train due to the periodic revivals of
molecular rotational wavepackets.
