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

Abstract

In this paper, a study of heat generation during UV laser-induced contamination (LIC) and potentially resulting subsequent thermal damage are 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, thus triggering chemical and photo-fixation reactions. This is a major hazard, in particular for laser units operating under vacuum conditions such as in space applications. The intense photon flux not only affects the contaminant deposition rate but also alters their chemical structure, which 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 assess the risk of the latter with the knowledge of temperature during the contamination process. For this purpose, a 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.

Analysis of laser-induced contamination at 515 nm in the sub-ps/MHz regime

“…There exists different experimental set-up in the scientific community to conduct laser-damage tests relevant to the study of LIC effect. Some of them were developed for LIC tests for space optics, 22,[24][25][26][31][32][33] with particular emphasis to exposure to nanosecond UV lasers. In this case, space conditions are simulated with a high vacuum chamber and the contamination process is controlled by introducing a specific contaminant into the chamber.…”

Direct Laser Synthesis of Ag Nanoparticles from Ammonia-alcoholic Solutions of AgNO3

“…As for temporal localization of the chemical reaction, the low pulse repetition rate -50 Hz gives the time interval between successive laser pulses much longer than the μs timescale for diffusion of heat out of the focal volume, so the next pulse arrives when the temperature drops to the initial temperature. 18,19 Thus, one can estimate the area of the chemical reaction as equal to 10 -8 cm 3 . For the solution concentration 0.1 M the amount of Ag in the reaction area is enough to create one 200 nm NP, and the size grows with solution concentration (C) according to 20 However, the sizes of the experimentally obtained NPs' are much smaller than the estimated ones, although the size growth tendency with concentration growth takes place.…”

Laser-induced contamination deposit growth mechanisms on space optics

“…The laserinduced temperature rise (ΔT ¼ c A F) for the highest used fluence is 1170 K, which is similar to previous measurements on differently LIC contaminated substrates. 24 For another cross check, we used a heat capacity value of C v ¼ 2.7 MJ∕ðm 3 KÞ (Ref. 25) for the hafnia layer and the known physical film thickness of 244 nm to calculate that 43 ppm of the light should be absorbed to obtain a temperature rise of 257 K at a fluence of 0.39 J∕cm 2 .…”