Laser damage mechanisms in conductive widegap semiconductor films.

Laser damage mechanisms of two conductive wide-bandgap semiconductor films - indium tin oxide (ITO) and silicon doped GaN (Si:GaN) were studied via microscopy, spectroscopy, photoluminescence (PL), and elemental analysis. Nanosecond laser pulse exposures with a laser photon energy (1.03 eV, 1064 nm) smaller than the conductive films bandgaps were applied and radically different film damage morphologies were produced. The laser damaged ITO film exhibited deterministic features of thermal degradation. In contrast, laser damage in the Si:GaN film resulted in highly localized eruptions originating at interfaces. For ITO, thermally driven damage was related to free carrier absorption and, for GaN, carbon complexes were proposed as potential damage precursors or markers.

High laser-resistant multilayer mirrors by nodular defect planarization [invited].

Substrate defect planarization has been shown to increase the laser resistance of 1053 nm mirror coatings to greater than 100 J/cm2, an increase of 20-fold, when tested with 10 ns laser pulses. Substrate surface particles that are overcoated with optical interference mirror coatings become nodular defects, which behave as microlenses intensifying light into the defect structure. By a discrete process of angle-dependent ion etching and unidirectional ion-beam deposition, substrate defects can be reduced in cross-sectional area by over 90%.

Monitoring annealing via CO(2) laser heating of defect populations on fused silica surfaces using photoluminescence microscopy.

Photoluminescence (PL) microscopy and spectroscopy under 266 nm and 355 nm laser excitation are explored as a means of monitoring defect populations in laser-modified sites on the surface of fused silica and their subsequent response to heating to different temperatures via exposure to a CO(2) laser beam. Laser-induced temperature changes were estimated using an analytic solution to the heat flow equation and compared to changes in the PL emission intensity. The results indicate that the defect concentrations decrease significantly with increasing CO(2) laser exposure and are nearly eliminated when the peak surface temperature exceeds the softening point of fused silica (approximately 1900K), suggesting that this method might be suitable for in situ monitoring of repair of defective sites in fused silica optical components.