Wavelength Dependence of Production of Multicharged Carbon Ions in Nanosecond Intense Laser Ionization of Seeded Benzene Beam

The photoionization of seeded benzene beam by 25 ns laser pulse at wavelengths of 266，355 and 1064 nm has been studied by the time-of-flight mass spectrometry. The observed mass spectra at 266 nm and 355 nm at intensities of 1010-1011 W/cm2 indicate a multiphoton ionization and dissociation（MPID）process，in which C+，C2Hx+，C3Hx+，C4Hx+ and C6H6+ are main products. While at 1064 nm laser of similar intensities，the domain ion is C4+ which is produced from Coulomb explosion. The longer wavelength facilities the energy absorption rate during inverse bremsstrahlung，which leads to the resulting wavelength dependence of the multicharged atomic ions.