Date of download: 6/3/2016 Copyright © 2016 SPIE. All rights reserved. Laser-beam path through the engine’s cylinder head for ignition-window testing (schematic). The focal distance could be set in order to have a determined cross section at the window. For reasons of simplicity the relative position of the components was not fixed rigidly. Figure Legend: From: Laser cleaning of optical windows in internal combustion engines Opt. Eng. 2007;46(10): doi: /

Date of download: 6/3/2016 Copyright © 2016 SPIE. All rights reserved. Contaminated windows tested under 50-Hz laser pulse irradiation during engine operation (samples 1 to 3). From (a) to (c), different focal spots have been set, resulting in different cleaning results. Figure Legend: From: Laser cleaning of optical windows in internal combustion engines Opt. Eng. 2007;46(10): doi: /

Date of download: 6/3/2016 Copyright © 2016 SPIE. All rights reserved. Window sample 4 after multiple pulsed laser shots from behind. The window had been contaminated before laser treatment. Optimum focal spots give best cleaning results without substrate damage, as microscopy of the marked area proves (see Fig. below). Figure Legend: From: Laser cleaning of optical windows in internal combustion engines Opt. Eng. 2007;46(10): doi: /

Date of download: 6/3/2016 Copyright © 2016 SPIE. All rights reserved. (a) Micrograph of ablated patches of sample 2 in Fig., and typical elemental composition of the window deposits (d) with and (c) without detectable laser influence. With efficient cleaning as in (b), the spectrum of the cleaned area is identical to that of an uncontaminated aluminum oxide nitride surface except for a very small amount of carbon. Figure Legend: From: Laser cleaning of optical windows in internal combustion engines Opt. Eng. 2007;46(10): doi: /

Date of download: 6/3/2016 Copyright © 2016 SPIE. All rights reserved. Erratic microcrystallite in the laser beam spot of sample 3 and corresponding element spectrum, making evident a blended compound. Such crystallites are supposed to be transparent to IR laser light, for which they do not greatly disturb the transparency of the window. Figure Legend: From: Laser cleaning of optical windows in internal combustion engines Opt. Eng. 2007;46(10): doi: /

Date of download: 6/3/2016 Copyright © 2016 SPIE. All rights reserved. Micrograph and element spectrum of the pulse-ablated site marked in Fig.. A few shots were sufficient to remove all the original deposits, but some minor carbon microparticles are seen as gray shadows in (a) and a weak element line in (b). The surface spectrum is dominated by the clean substrate lines of Al and O. Figure Legend: From: Laser cleaning of optical windows in internal combustion engines Opt. Eng. 2007;46(10): doi: /