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Featured Application: laser surface-processing. Monocrystalline barium fluoride (BaF2) slab targets were irradiated by focused 46.9-nm laser radiation at various fluence levels above the ablation threshold. Well-developed ablation patterns with sharp edges were studied by AFM (atomic force microscopy). Their inner surfaces were uniformly covered by periodic structures. The spatial period of the ripples depends on the laser fluence. When the sample is rotated by 45°, the orientation of the grating-like structure changes accordingly. Thus, the grating vector of the periodic structure seems to be coupled to the crystallographic planes of the single crystal. This means that the XUV-laser induced ripples reported here differ from LIPSS (laser-induced periodic surface structures) associated with interference phenomena occurring on illuminated surfaces. Therefore, other mechanisms are discussed to explain the formation of the periodic nanostructures reported in this article. [ABSTRACT FROM AUTHOR]

Abstract: Barium Fluoride (BaF2), mainly used in optical applications, has similar properties to those of CaF2 but better stability under environmental conditions. In this paper, we report measurements of loss tangent and the real part of the relative permittivity ε r of single crystal BaF2 in the temperature range from 14 to 290K at frequencies of 8, 10.4, 12.1, 17.6, 21.1 and 24.4GHz. Microwave properties of BaF2 were determined by measurements of the resonance frequency and the unloaded Q-factor of TE011 and quasi TE0mn modes cylindrical cavities containing the sample under test. Two techniques namely Hakki–Coleman Dielectric Resonator and dielectric post resonators have been used for characterizing the dielectric material. Losses due to the uncalibrated cables and adaptors inside the cryocooler are accounted in the calculation of unloaded Q-factor using the Transmission Mode Q-Factor data processing technique. The permittivity of BaF2 exhibited a 5% increase from 6.9 (14K) to 7.35 (290K). The loss tangent increased from 1×10−5 to 1.1×10−4 over the measured temperature range, 14–290K at a frequency of 10.4GHz. The measured microwave properties show that BaF2 can be used in many microwave devices. [Copyright &y& Elsevier]

YbF-doped BaF crystals with various concentrations of YbF (0.05, 0.1, 0.17, 0.2 mol) have been grown using the conventional Bridgman method. Dielectric relaxation is used to study the charge compensating defects in BaF crystals with low YbF concentration. The optical absorption spectra reveal the existence of both Yb (in UV domain) and Yb (in IR domain) ions. In the investigated temperature range (150-320 K) we have observed only one type of dielectric relaxation. This relaxation with activation energy eV is associated with trigonal-type () centers. The charge compensating defects are discussed while taking also into account the optical absorption spectra and the calculated number of NNN dipoles whose relaxation is observed. [ABSTRACT FROM AUTHOR]