| Popis: |
We previously reported on the deposition, absorption, and CO 2 -laser damage threshold for As 2 S 3 , As 2 Se 3 , and NaF coatings. It was shown that the damage threshold was much lower for coated than uncoated substrates and that the mechanism for damage was different in the coatings than in the substrates. We speculated that the damage in the coatings was related to the presence of micron-sized crystalline defects distributed in the amorphous chalcogenide matrix. In this paper we report the results of damage measurements on these materials at 2.8 and 3.8 μm and identify two operating damage processes: "uniform" damage, which we associate with the amorphous chalcogenide matrix, and "selective" damage, which we associate with the crystalline defects. For single-layer films, we find that N/1 conditioning generally produces an increase in the damage thresholds. The wavelength dependence of multithreshold results in single-layer coatings of As 2 S 3 and NaF suggests that improvement in threshold results from the thermal desorption of contaminating layers of water at 2.7 μm. However, for a dielectrically enhanced reflector containing quarter-wave layers of As 2 Se 3 and NaF, N/1 conditioning promoted crystallite growth which resulted in a definite deterioration of N/1 thresholds. |
