Resistance of optical and colored glasses to 3-nsec laser pulses

In the experimental setup, the pulse of a Nd:YAG glass laser (1060-nm wavelength, 3-nsec pulse duration, output energy up to 1 J) generated damage at the surface and in the bulk of optical glasses. The slightly focused beam exhibited a 2-mm diam in the sample plane with a peak energy density of up to 50 J/cm(2). The surface damage was investigated on 5-mm thick samples with a differential interference microscope (Nomar-ski). In most cases, the damage was small pits probably caused by absorption centers in the polishing layer. Thresholds were more dependent on the polishing method than on the chemical composition of the glass. Typical values ranged from 15 to 25 J/cm(2) for optical glasses and from 8 to 25 J/cm(2) for colored glasses. Studies of internal damage using 20-mm thick samples showed two phenomena: threadlike and pointlike damage at different thresholds. Threadlike damage was caused by self-focusing of the laser beam and was therefore correlated with the nonlinear refractive index of the sample. Inclusions within the glass are responsible for the pointlike damage. Internal damage thresholds varied from 7 to more than 45 J/cm(2). Glass types BK-1, BK-7, TiK-1, BaK-2, ZK-1, PSK-50, and BaLK-3 show high resistance.