Laser induced deposits in contaminated vacuum environment: Optical properties and lateral growth

Abstract The lifetime of high power photonics instruments operating in vacuum is often strongly reduced due to an effect designated as Laser Induced Contamination (LIC): Outgassing from polymers generates molecular contamination on the optical components and the interaction between the laser beam and the contaminants induces the growth of an often carbonaceous deposit. The LIC deposit then partly absorbs the laser pulses which leads to fast reduction of the instrument performances. In this study, we generated LIC deposits using a nanosecond laser at 355 nm. Toluene and the outgassing products from an epoxy adhesive are used as contaminants. We then analyzed the optical properties of different zones of the 100 µm large and 10 nm thick deposit using advanced optical techniques. These data will be useful for numerical simulations of the deposit evolution. We also investigated the mechanism of the lateral growth of the crater-shaped deposit and found strong indications that heat conduction from the center of the deposit sustains the lateral growth into regions where the local fluence is small.