Spectroscopic evidence of multiphoton absorption in nitrogen

Nitrogen pressure ∼2 Torr provides conditions which allow the spectroscopic study of the multiphoton absorption processes under the action of a neodymium glass laser radiation. From the laser flux dependence of the light intensity emitted by different excited states of nitrogen, we point out various absorption processes leading to the ionization and dissociation of the molecule and to the ionization of the atom.