Efficient mid IR (1.5-2.2 µm) Raman lasers based on novel BaWO 4 and known Ba(NO 3 ) 2 Raman crystals were developed and investigated. Different Stokes shifted components were obtained with longest wavelength about 2.2 µm with efficiency up to 10%. Main informationNowadays great attention is paid to the development of novel lasers oscillating in mid IR spectral range (2-5 µm) where the lack of laser sources (especially within 3-5 µm range) is quite noticeable. There are several approaches towards development of laser sources for mid IR spectral region: development of new solid state laser media, molecular gas lasers, OPO generators etc. One of the promising approaches is Raman shifting of the available laser sources towards mid IR range. The main problem here is that most of the Raman crystals' frequency shift is about 1000 cm −1 , so to obtain mid IR radiation one should start from as long wavelength as possible and obtain second or even third Stokes shifted components. At the same time it should be kept in mind that Raman gain drops rapidly with longer wavelength pump, so that stimulated Raman scattering threshold intensities become separated from the crystal optical damage threshold intensities by rather narrow interval making Raman lasing a sort of challenge. Another problem for mid IR Raman lasing is that a lot of well known efficient Raman crystals are opaque in this spectral range due to the matrix absorption.The newly developed barium tungstate crystals are proved to be efficient source for both picosecond and nanosecond time scale Raman lasing [1]. Our results on stimulated Raman scattering under nanosecond IR pumping in comparison with the well-known barium nitrate crystal showed rather close thresholds and conversion efficiency. Though BaWO 4 crystals are much further transparent and allows obtaining Raman shifted radiation up to 3 µm.As the initial pump source the 1.34 µm YAG:Nd 3+ laser and 1.53 µm Er:Glass laser were applied. These lasers were selected due to their longest lasing wavelengths where short Q-switched pulses can be rather reliably obtained. In our experiments accousto-optically Qswitching for Nd:YAG laser and passive Q-switching by Co 2+ :spinel crystal for Er:Glass laser were applied which allowed to obtain pulses with 40-50 ns duration in both cases. This lasers served as pump sources for 80 mm long BaWO 4 crystal or 50 mm long Ba(NO 3 ) 2 crystal based Raman lasers with the cavity formed by a rear plain HR mirror with 90-100% reflectivity within oscillating spectral range and about 80% transmittance at pumping wavelengths. To optimize first, second or third Stokes
Hydration and dehydration (on calcination) of SrCl 2 , YOCl, and HoOCl powders were studied.Single-crystal chloride materials are of interest for photonics owing to their transparence in the IR range and a [soft] photon spectrum. The main problem in both growing the crystals and working with them is their hydration. In particular, chlorides of rare-earth elements are very hygroscopic; hydrated rare-earth chlorides are readily hydrolyzed on heating [13 6]. This substantially complicates the use of such materials, though the spectroscopic characteristics, e.g., of LaCl 3 : R 3+ single crystals are highly promising [7]. Among matrices resistant to moisture are PbCl 2 and KPb 2 Cl 5 [8310].In this study we examined the hydration of SrCl 2 powders and also of oxychlorides of rare-earth elements. Strontium chloride crystallizing in a cubic lattice of the fluorite type has a high isomorphous capacity with respect to chlorides of rare-earth elements [11]. Properties of SrCl 2 single crystals and of Sr 1 !x R x Cl 2 + x solid solutions have been studied repeatedly [12314]. Oxychlorides of rare-earth elements are more resistant to moisture than the chlorides [15]. Therefore they could be a convenient form for introducing dopants.We used ultrapure 73 4 grade SrCO 3 , chemically pure grade ammonium chloride NH 4 Cl, and chemically pure grade hydrates of rare-earth elements RCl 3 . 6H 2 O as starting substances. The initial chemicals were characterized by X-ray diffraction. The X-ray phase analysis was carried out on a DRON-2 diffractometer (CuK = radiation, focusing monochromator from pyrolytic graphite). We recorded variations in sample weights on an Acculab V-200 electron balance. The humidity was measured with a psychrometer. The hydration was carried out at 19 + 2oC and the relative humidity of 38 + 5%.We prepared strontium chloride by the reaction SrCO 3 + 2NH 4 Cl = SrCl 2 + H 2 O8 + CO 2 8 + 2NH 3 8. (1) We used a fourfold excess of NH 4 Cl. The reaction was carried out in an alundum crucible at 150 3350oC for 6 h. The yield of SrCl 2 was 99%. The resulting SrCl 2 had a cubic fluorite-type lattice with a = 6.977 A, which agrees with the published data (PDF card no. 38-0496). On exposure to air, the sample weight continuously increased; the process gradually decelerated with time (Fig. 1). The increase in the substance weight in the first hour was 7%. The increase in the sample weight was accompanied by changes in its X-ray pattern. Along with the SrCl 2 lines, an additional set of reflections appeared, and their intensities rapidly increased, whereas the lines of SrCl 2 weakened (Fig. 2). Analysis of the pattern using the PDF database revealed mixture of mono-, di-, and hexahydrates of SrCl 2 . The final hydration product was SrCl 2 . 6H 2 O. On calcination of strontium chloride hexahydrate at 350oC for 2 h, the weight loss corresponded to complete dehydration. The subsequent Dm, g t, h Fig. 1. Kinetics of SrCl 2 hydration. (,m) Change in the weight of the sample and (t) time.
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