Laser-induced hydrocarbon contamination in vacuum

Abstract

We investigated laser-induced deposition processes on BK7 substrates under the influence of pulsed Q-switched Nd:YAG laser radiation, starting from small toluene partial pressures in a background vacuum environment. The composition and structure of the deposit was analyzed using microscopic methods like Nomarski DIC, dark-field and white-light interference microscopy, TEM, EDX and XPS. We found a distinct threshold for deposition built-up dependant on the partial pressure of toluene (0.2 J/cm 2 at 0.1 mbar, 0.8 J/cm 2 at 0.01 mbar toluene). The deposits strictly followed the spherical geometry of the laser spot. No deposit accumulated on MgF 2 AR coated BK7 samples even at high toluene partial pressures. The onset of deposit was accompanied by periodic surface ripples formation. EDX and XPS analysis showed a carbon-like layer which strongly absorbed the 1 µm laser radiation. The typical number of shots applied was 50 000. In addition, long term lifetime tests of more than 5 Mio. shots per site were run.

Femtosecond pulse damage thresholds of dielectric coatings in vacuum

“…Previous studies with nanosecond lasers under vacuum and sealed atmospheric conditions have shown that the useful lifetime of the optics and multiple pulse damage fluence reduced significantly for dielectric films [5][6][7][8] and bulk materials [9,10] compared to atmospheric conditions. Two explanations have been given for these observations.…”

Improvements in long-term output energy performance of Nd:glass regenerative amplifiers

“…LIC was proposed by Wernham et al during the research of frequency-tripped Nd:YAG lasers on space [11][12][13][14] . According to their research, LIC is caused by the interaction of the laser with molecules which outgas from organic materials in vacuum on the optical surfaces, and it will form highly absorbing deposits on the surface of optics.…”

“…Therefore, finding out origin of these optical damages is the priority to improve operation lifetime of the Regen. There are two possible reasons for such optical damages: one is that damage threshold of optical components in Regen cavity may be not high enough to prevent laser induced damages (LIDs), which result from defects on the surfaces or in the bodies of these components [8][9][10] ; the other is that laser induced contamination (LIC) may happened on the surfaces of optical components in the Regen cavity, i.e., the formation of highly absorbing deposits on optical surfaces caused by the interaction of the laser with molecules which outgas from organic materials in vacuum or molecules of dust and gas in contaminated air environment [11][12][13][14] . LIC results in degradation of the properties of optical components, which contributes to an overall transmission loss and eventual irreversible damages of optical components.…”

A new ECSS standard for environmental durability testing of optical coatings for space application

“…Specific test methods have recently been developed in the frame of ESA's Aeolus and Earthcare satellites [4]. For LIC testing, the coating is exposed to the laser beam in the presence of organic materials, and the resulting transmission loss is measured.…”