Optical properties of CaF[sub]2[/sub] and Yb[sup]3+[/sup]:CaF[sub]2[/sub] for laser applications

Jörg Stäblein; Karin Pöhl; Andreas Weisleder; Gordon v. d. Gönna; Thomas Töpfer; Joachim Hein; Mathias Siebold

doi:10.1117/12.886830

9 June 2011 Optical properties of CaF₂ and Yb³⁺:CaF₂ for laser applications

Jörg Stäblein, Karin Pöhl, Andreas Weisleder, Gordon v. d. Gönna, Thomas Töpfer, Joachim Hein, Mathias Siebold

Proceedings Volume 8080, Diode-Pumped High Energy and High Power Lasers; ELI: Ultrarelativistic Laser-Matter Interactions and Petawatt Photonics; and HiPER: the European Pathway to Laser Energy; 808002 (2011) https://doi.org/10.1117/12.886830
Event: SPIE Optics + Optoelectronics, 2011, Prague, Czech Republic

Abstract

Highly transparent CaF₂ has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF₂ single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb³⁺ doped CaF₂ crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb³⁺ /Yb²⁺ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

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Jörg Stäblein, Karin Pöhl, Andreas Weisleder, Gordon v. d. Gönna, Thomas Töpfer, Joachim Hein, and Mathias Siebold "Optical properties of CaF₂ and Yb³⁺:CaF₂ for laser applications", Proc. SPIE 8080, Diode-Pumped High Energy and High Power Lasers; ELI: Ultrarelativistic Laser-Matter Interactions and Petawatt Photonics; and HiPER: the European Pathway to Laser Energy, 808002 (9 June 2011); https://doi.org/10.1117/12.886830

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