Speaker
Description
Laser induced contamination (LIC) is a critical issue optical systems operating with high-power lasers, particularly in the ultraviolet (UV) range, face. These lasers form part of Light Detection And Ranging (LiDAR) missions such as ADM-Aeolus and EarthCARE.
The smallest amounts of outgassed contaminants originating from adhesives, coatings and other materials can significantly affect the lifetime and reliability of optical systems. This is due to cold optical surfaces, such as mirrors and lenses, acting as preferred deposition sites for outgassed molecules. Although the initial contamination layers may be of very low thickness and with limited optical impact, exposure to high-power UV radiation can substantially alter their physical and chemical properties. The laser’s high photon energy exceeds most molecular bond energies, driving photochemical and thermally activated effects in the outgassed species. These reactions include molecular fragmentation, recombination, polymerisation and cross-linking, leading to a chemically and structurally modified contamination layers with properties depending on both the originating material and the irradiation conditions. The resulting deposits exhibit increased optical absorption and scattering, leading to permanent laser energy losses and elevated thermal loading of optical surfaces. Ultimately, this degradation can result in reduced system performance, failure through insufficient transmitted laser energy or the onset of laser‑induced damage (LID) of the optics.
This work makes use of the newly commissioned Radiation Induced Environmental Effects Facility (RIEEF) at ESTEC to investigate the formation and evolution of LIC under controlled, space‑relevant conditions. The facility enables systematic and parameterised studies of contamination behaviour as a function of temperature, pressure, laser energy density, and contamination source. In-situ monitoring of contamination levels is performed by using a quartz crystal microbalance (QCM) as well as laser induced effects are observed via laser induced fluorescence (LIF) measurements (based on CCD based fluorescence imaging) and laser energy diagnostics. Post-test characterisation of the contamination layers includes optical transmission loss measurements using UV/Vis/NIR spectrophotometry, as well as chemical and structural analysis by Fourier Transform Infrared (FTIR) spectroscopy and Raman microscopy. Further planned analyses include X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) to provide additional insight into the surface chemistry and morphology of the deposits. These results contribute to an improved understanding of LIC mechanisms and support the development of laser-based contamination detection and mitigation strategies for future space laser missions.