Influence of oil contamination on the optical performance and laser induced damage of fused silica

• The optical performances of contaminated fused silica were investigated.
• The photo-thermal absorption of the contaminated layer was investigated.
• The light intensity modulation is numerically calculated.
• The damage mechanism was discussed.

The influence of oil contamination on the optical performance of fused silica and laser induced damage threshold (LIDT) at 355 nm is studied. The liquid vacuum oil is artificially spun on the fused silica surface. Optical microscopy and ultraviolet–visible (UV–vis) spectrophotometer are used to identify and understand the potential influence of oil contamination on the optical performance of fused silica. The results show that a large number of oil droplets are observed on the surface of fused silica after spin-coating, and the transmissivity of fused silica decreases with the increasing oil quantity. The LIDTs of fused silica decrease with the increasing oil mass for both on input and output surfaces at 355 nm, and the LIDT of fused silica with oil on input surface is lower than that on output surface at same contamination level. The damage mechanisms are also discussed by the photo-thermal measurement and three dimensional finite difference time domain (3D-FDTD) method. The experimental and simulated results show that the electric-field modulation by oil droplets, rather than its photo-thermal absorption, is mainly responsible for the oil contamination induced laser damage of fused silica.