Laser-wavelength effect of production of multicharged krypton ions in intense nanosecond laser ionization of krypton clusters

The photoionization of krypton atomic clusters by 25 ns laser pulses with wavelengths of 266, 355, 532 and 1064 nm was studied using time-of-flight mass spectrometry at intensities of 1010-1011 Wcm-2. The distinguished highest charge of the multi-charged ions is +2,+4,+11 and +17, while the lasers with the above wavelengths illuminate the Kr atomic clusters in turn. It is indicated that the charge states of Kr ions significantly depend on laser wavelength, rather than depend on laser intensity. The results further support the three stage model of multiphoton ionization inverse bremsstrahlung heating and electron impact ionization.