30 December 2008 Interaction of high-power infrared radiation with germanium
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We have observed and characterized wavelength-dependent laser damage thresholds in crystalline germanium induced by trains of high-power infrared picosecond laser pulses at wavelengths ranging from 2.8 μm to 5.2 μm, using the Vanderbilt Free-Electron Laser. In this wavelength range, photon energies are well below the band-gap energy. As the wavelength is increased, threshold fluences are observed to increase by a factor of five over the studied wavelength range. Two- and three- photon absorption is the predominant photon energy absorption mechanism up to 4.4 μm. At wavelengths above 4.8 μm tunnel absorption appears to be the primary absorption mechanism. Wavelength and fluence dependent transmission and reflection measurements provide valuable insight into the nature of the damage mechanisms.
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D. Seo, D. Seo, L. C. Feldman, L. C. Feldman, N. H. Tolk, N. H. Tolk, P. I. Cohen, P. I. Cohen, } "Interaction of high-power infrared radiation with germanium", Proc. SPIE 7132, Laser-Induced Damage in Optical Materials: 2008, 713216 (30 December 2008); doi: 10.1117/12.816611; https://doi.org/10.1117/12.816611

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