Effect of polarization on two-color laser-induced damage

Laserinduced damage of optical materials due to the presence of radiation at two different frequencies has received little attention in the literature even though this is not an uncommon occurrence in the laboratory. Recent studies on the inultiphoton ionization of single atoms have shown that the ionization threshold depends strongly on the frequencies of the incident fields and their polarizations. In this paper we explore the extent to which these results can be applied to laserinduced damage. The results for a single atom are presented for the case where one field has a comparatively high frequency and low intensity. This field is responsible for the ionization. The other field has a higher intensity and much lower frequency such that it does not ionize by itself. However it substantially modifies the ionization threshold due to the first field. Both fields are circularly polarized. The behavior of the ionization rate near the thresholds is found to depend strongly on whether the fields have the same or opposite circular polarizations. We also speculate on how these results will influence laser induced damage thresholds.