Single-shot coherent control of molecular rotation by fs/ns rotational coherent anti-Stokes Raman spectroscopy

We present a novel method, to our knowledge, to control the shape of the spectra using 2-beam hybrid femtosecond (fs)/nanosecond (ns) coherent anti-Stokes Raman scattering (RCARS). The method is demonstrated experimentally and theoretically by utilizing a species-selective excitation approach via a field-free molecular alignment as an illustrative example. Two non-resonant fs laser pulses with proper delay selectively create and then annihilate N₂ resonances in a binary mixture with O₂ molecules. The RCARS signal is simultaneously resolved in spectral and temporal domains within a single-shot acquisition. The method requires very low pulse energies for excitation, hence minimizing multiphoton ionization probability, allowing for coherent control at various temperatures and pressures, with spectroscopic applications in non-stationary and unpredictable reacting flows.