Molecular Rotational Effects in Free-Space N+ 2 Lasers Induced by Strong-Field Ionization

Abstract

Free-space\( \kern0.28em {\mathrm{N}}_2^{+}\kern0.28em \)lasers induced by strong-field ionization have shown a great potential for the standoff diagnostics of quantum rotational wave packets in air molecules and for the fingerprint identification of chemical species, thanks to their capability of remotely generating intense, narrow-bandwidth, coherent emissions. It has been observed that the laser signals are strongly influenced by the dynamics of the rotational wave packets in the \( {\mathrm{N}}_2^{+} \) ions produced by photoionization in the intense laser fields. This chapter gives an overview of the experimental results of the effects of molecular rotations in the free-space \( {\mathrm{N}}_2^{+} \) lasers. We will begin with the description of the ultrafast dynamics of coherent rotational wave packets using the \( {\mathrm{N}}_2^{+} \) laser as an optical probe. We will follow with a discussion of the coherent coupling of the rotational quantum states in a strong laser field, manipulation of the polarization of \( {\mathrm{N}}_2^{+} \) laser emission, and the observation of impulsive rotational Raman scattering induced by the \( {\mathrm{N}}_2^{+} \) laser. Finally, a summary and perspective will be given.