<title>Laser-induced damage of fused silica at 355 and 1064 nm initiated at aluminum contamination particles on the surface</title>

Abstract

Contamination particles of controlled size and shape were deposited onto 1.14 cm thick fused silica windows by sputtering Al through a mask. The particles were 1 µm thick circular dots, 10 to 250 µm in diameter. Al shavings were also deposited on the windows to investigate the effects of particle-substrate adhesion. The silica windows were then illuminated repetitively using a 3-ns, 355 nm and an 8.6-ns, 1064 nm laser. The tests were conducted at near normal incidence with particles on the input and output surfaces of the window.During the first shot, a plasma ignited at the metal particle and damage initiated on the fused silica surface. The morphological features of the damage initiated at the metal dots were very reproducible but different for input and output surface contamination. For input surface contamination, minor damage occurred where the particle was located; such damage ceased to grow with the removal of contaminant material. More serious damage (pits and cracks) was initiated on the output surface (especially at 355 nm) and grew to catastrophic proportions after few shots. Output surface contaminants were usually ejected on the initial shot, leaving a wave pattern on the surface. No further damage occurred with subsequent shots unless a shot (usually the first shot) cracked the surface; such behavior was mostly observed at 355 nm and occasionally for large shavings at 1064 nm.The size of the damaged area scaled with the size of the particle (except when catastrophic damage occurred). The onset of catastrophic damage on the output surface occurred only when particles exceeded a critical size. The damage behavior of the sputtered dots was found to be qualitatively similar to that of the shavings. The artificial contamination technique accelerated the study by allowing better control of the test conditions.

Rear-surface laser damage on 355-nm silica optics owing to Fresnel diffraction on front-surface contamination particles

“…9 -17 Such diffraction effects have become increasingly more noticeable in the fields of laser processing 7 and laser-induced damage. 5,6,18,19 Diffraction produces downstream light-intensity modulations that are often noticed in the image plane when particles of dust land upon optical components. When such contam-ination particles fall in the path of a powerful laser beam, they can sometimes initiate laser-induced damage 5,6,9,20 -22 or trigger self-focusing.…”

“…[27][28][29][30][31][32][33][34] A range of different types of optical material ͑e.g., fused silica, KDP, hafnia-silica multilayers, Nd-doped laser glass͒ was investigated for determination of the contamination level that could be tolerated during peak intensity operation on the laser beams of the National Ignition Facility and the Laser Méga Joule. 5,22 The initial goal of the study reported here was to quantify systematically the drop in laser-induced-damage threshold of fused silica at 355 nm caused by contamination particles ͑various contaminant sizes, shapes, and materials͒ on input and output surfaces. As the study progressed and damage morphologies were being characterized, it became clear that diffraction of light by input-surface obscurations, and sometimes by rare bulk inclusions, contributes to decreasing the damage threshold of output surfaces.…”

High Repetition-Rate Laser Z-Scan Measurements: Criterion for Recognizing Adverse Thermal Effects

“…The results are depiced in Figure 3 in which (a)-(c) show the residual manufacturing defects left on the surface of the glass through polishing (Genin, Feit, Kozlowski, Rubenchik, Salleo, & Yoshiyama, 2000;Honig, Norton, Hollingsworth, Donohue, & Johnson, 2005;Salleo, Genin, Yoshiyama, Stolz, & Kozlowski, 1998). On the other hand, Figure 3(d)-(f) show microexplosions triggered by irradiation of surface contaminants of the fused-quartz cuvettes using the high pulse repetition-rate laser (Genin, Feit, Kozlowski, Rubenchik, Salleo, & Yoshiyama, 2000;Honig, Norton, Hollingsworth, Donohue, & Johnson, 2005;Salleo, Genin, Yoshiyama, Stolz, & Kozlowski, 1998;Genin, Michlitsch, Furr, Kozlowski, & Krulevitch, 1997). To further investigate the damage results shown in Figure 3, open aperture z-scan studies were carried out using empty damaged fused-quartz cuvettes at both 76MHz and the pulse-picked repetition rate of 152Hz and the results are displayed in Figure 4.…”

<title>Optical cleanliness specifications and cleanliness verification</title>

“…Ample evidence exists that particulate contamination initiates damage on both bare and coated optical surfaces in the presence of high intensity laser light [1]. More recently, it has been found that flashlamp light is sufficient to create aerosols within laser amplifier cavities and that the these aerosol particles subsequently settle onto laser amplifier slabs and initiate pitting damage to the optical surface [2].…”