MULTIPHOTON IONIZATION AND DISSOCIATION OF N-2 AT HIGH LASER INTENSITY

This work reports the five- and nine-photon ionisation of the N2 molecule in the nanosecond range with laser intensity up to 1014 W cm-2. Both ion mass spectra and photoelectron energy distributions are recorded. At 694.3 nm the authors demonstrate the absorption of six photons above the ionisation threshold (ATI) populating a unique vibrational level (X 2 Sigma +g, nu +=0) which is subsequently dissociated into N(2DO) atomic fragments by absorption of seven photons. At 347.1 nm the N+2 vibrational population is distributed over X 2 Sigma +g, nu +=0-3 and A 2 Pi u, nu +=0-5 levels which then dissociate into N( 2DO) and N(4S degrees ) by absorption of three or four photons. The effects of the high laser intensity are discussed.