Comparative studies of absorptance behaviour of alkaline-earth fluorides at 193 nm and 157 nm |
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Authors: | C Görling U Leinhos K Mann |
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Institution: | Laser-Laboratorium G?ttingen, Hans-Adolf-Krebs-Weg 1, 37077 G?ttingen, Germany, DE
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Abstract: | Absorptance losses in MgF2, CaF2 and BaF2 during 193-nm (DUV) and 157-nm (VUV) irradiation are investigated by employing a high-resolution laser calorimetric technique
which allows the determination of both single- and two-photon absorptance at energy densities up to 110 mJ/cm2. A strong wavelength dependence of the DUV and VUV absorption characteristics is observed: while effective two-photon absorption
takes place at 193 nm, either no similar effect at all (in the case of BaF2) or only a very minor effect (CaF2) is observed at 157 nm. A first explanation for this absorption behaviour is given, implying the energetic band structure
of CaF2. In addition it is shown that, due to the strong nonlinear dependency, above a critical energy density the absorptance at
193 nm can exceed the absorptance at 157 nm. Furthermore, different single- and two-photon absorption coefficients are determined
for different CaF2 samples at 193 nm, indicating a two-step absorption mechanism. In addition, laser-induced aging is found in a MgF2 sample at 193 nm, but not at 157 nm.
Received: 21 June 2001 / Revised version: 2 November 2001 / Published online: 7 February 2002 |
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Keywords: | PACS: 42 70 -a 42 87 -d 78 20 Ci 42 65 61 80 |
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