Cluster-assisted generation of multi-charged ions in nanosecond laser ionization of pulsed hydrogen sulfide beam at 1064 and 532 nm

摘要

The multi-charged sulfur ions of Sq+ (q = 6) have been generated when hydrogen sulfide cluster beams are irradiated by a nanosecond laser of 1064 and 532nm with an intensity of 10(10) similar to 10(12) W(.)cm(-2). S6+ is the dominant multi-charged species at 1064 nm, while S4+, S3+ and S2+ ions are the main multi-charged species at 532 nm. A three-step model (i.e., multiphoton ionization triggering, inverse bremsstrahlung heating, electron collision ionizing) is proposed to explain the generation of these multi-charged ions at the laser intensity stated above. The high ionization level of the clusters and the increasing charge state of the ion products with increasing laser wavelength are supposed mainly due to the rate-limiting step, i.e., electron heating by absorption energy from the laser field via inverse bremsstrahlung, which is proportional to lambda(2), lambda being the laser wavelength.