<title>Characterization of optical coatings: damage threshold/local absorption correlation</title>

Abstract

Simultaneous absorption and scattering mappings are used to study the influence of local defects on the laser damage threshold of thin films. The same area is mapped for absorption and scatter before and after irradiation at the threshold fluence. The study is performed for an uncoated fused silica substrate and two single-layer films deposited on fused silica substrates at a wavelength of x = 1 .06 jim.Initial results seem to indicate that the irradiation can create and enhance absorption and scattering defects. This study is conducted as part ofthe Megajoule laser project.

Photothermal multipixel imaging microscope

“…Photothermal microscopy over a square millimeter has been demonstrated by multiple groups. 7,[10][11][12][13][14][15][16][17] High-resolution scans over a square centimeter has not yet been demonstrated until now as illustrated in figure 7. The interest of our group is in the "quick" identification of the highest absorbing defects within an optical coating.…”

“…Fluence-limiting defects in optical coatings can be differentiated from benign defects with photothermal microscopy. [1][2][3][4][5][6][7] Defects with little photothermal signal survive significantly higher fluences than defects with high photothermal signal. In fact, a linear relationship has been demonstrated between photothermal signal and laser damage threshold.…”

Engineering meter-scale laser resistant coatings for the near IR

“…Photothermal microscopy experiments clearly illustrate that some defects with significant absorption may not be optically visible as opposed to nodular defects with diameters up to tens of microns in diameter that are easily observed with an optical microscope. [14][15][16][17][18] Post mortum focused-ion beam cross section (figure 2) inspection of these defects revealed in one particular study, 14 these defects had such low laser resistance that they were damaged by the pump beam of the photothermal microscope. Analysis of these images suggested a very small initiator that caused thermal-induced buckling of the surrounding multi-layer structure.…”