Real-time measurement of temperature variation during nanosecond pulsed laser induced contamination deposition

In this paper a study of the heat generation during UV Laser Induced Contamination (LIC) and potentially
resulting subsequent thermal damage is presented. This becomes increasingly interesting when
optics with delicate coatings are involved. During LIC radiation can interact with outgassing molecules
both in the gas phase and at the surface, triggering chemical and photo-fixation reactions. This is a major
hazard, in particular for laser units operating under vacuum conditions such as for space applications.
The intense photon flux not only affects the contaminant deposition rate but also alters their chemical
structure that can increase their absorption coefficient. Over cumulative irradiation shots these molecules
formed deposits that increasingly absorb photons and produce heat as a by-product of de-excitation eventually
leading to thermal damage. One could better asses the risk of the latter with the knowledge of
temperature during the contamination process. For this purpose thermoreflectance technique is used here
to estimate the temperature variation from pulse to pulse during contamination deposition through the
analysis of a temperature-dependent surface reflectance signal.