Enhanced resonant vibrational Raman scattering of N₂⁺ induced by self-seeding ionic lasers created in...

We report on an experimental investigation of the five vibrational Raman lines at 358 nm, 388 nm, 391 nm, 428 nm, and 471 nm of N2+ resonantly driven by the self-seeding ionic lasers generated by a polarization-modulated (PM) or alternatively a linearly polarized (LP) femtosecond laser. It was found that the spectral intensities of several Raman lines can be dramatically enhanced by exploiting the PM laser pulses in comparison to the LP laser pulses. The evaluated Raman conversion efficiency reaches ∼10^-2 for some lasing lines at suitable pressures. Moreover, the role of interplay between the seed amplification and the resonant vibrational Raman scattering processes in inducing the gain of N2+ lasing is characterized for the first time. The developed vibrational Raman spectroscopy with intense ultrafast lasers provides an additional approach to interrogate the products in a femtosecond filament, and it therefore can be a powerful tool for identifying chemical species at remote distances in the atmosphere.