Wavelength-dependence of laser-induced damage in fused silica and fused quartz

Laser-induced damage threshold (LIDT) of various types of vitreous silica at 1064, 532, 355 and 266 nm was investigated. At 1064 nm no difference of LIDT was observed for all samples. At 1064-355 nm, wavelength-dependence of LlDT of synthetic fused silica (SFS) can be well described by a relation I-th = 1.45 lambda (0.43), where I-th is LIDT in J/cm(2) and lambda is wavelength in nm. At 266 nm, however, LIDTs were smaller than a half of the calculated value from above relation. This difference can be explained by the damage mechanism; at 266 nm, two-photon absorption-induced defects lowered the LTDT same as a KrF-exicmer-laser induced defects, whereas at longer wavelengths two photon process does not occur, LIDTs of fused quartz (FQ) at 532 and 355 nm, and that of a SFS containing about 1000 ppm of Cl and no OK at 355 nm were a little lower than that of the other SFSs. This may be related to the absorption of metallic impurities contained in FQ and dissolved Cl-2 molecule in SFS.