Andrey G. Okhrimchuk

Near-infrared luminescence of RbPb2Cl5:Bi crystals.

A wideband near-IR (NIR) luminescence centered at 1080 nm was found in a RbPb(2)Cl(5):Bi single crystal grown by the Bridgman technique. Absorption, luminescence, and excitation of luminescence spectra were investigated at room and cryogenic temperatures. The luminescence was proposed to be due to the (3)P(1)-->(3)P(0) transition in Bi(+) ion.

Optical spectroscopy of the RbPb 2 Cl 5 :Dy 3+ laser crystal and oscillation at 5.5 μm at room temperature

Oscillation at 5.5μm wavelength has been investigated in the low-phonon, moisture-resistant RbPb2Cl5:Dy3+ crystal in free-running mode at room temperature. In line with our knowledge this is the longest laser wavelength for a rare-earth doped crystal that does not require any special precautions for survival. Spectra and kinetics of luminescence of the new laser crystal were investigated under pumping to 1.3 μm absorption band, corresponding to lasing experiments. Emission cross sections were determined for mid-IR transitions. It was found that emission cross section on the 6H9/2+6F11/2→6H11/2 laser transition at 5.5 μm wavelength is as high as 0.6×10−20cm2.

Preparation and optical properties of rare-earth-activated alkali metal lead chlorides

High-purity MPb2Cl5 (M = K, Rb) and MPbCl3 (M = Rb, Cs) salts were prepared by directional solidification and zone melting of stoichiometric mixtures. The Bridgman method was used to grow crystals of rare-earth-activated double salts: KPb2Cl5:(Tb3+, KPb2Cl5:(Tb3+, Tm3+), KPb2Cl5:Dy3+, KPb2Cl5:Pr3+, RbPb2Cl5:Dy3+, and RbPb2Cl5:Pr3+. Analysis of their room-temperature IR absorption and luminescence spectra suggests that these crystals are potential materials for mid-IR solid-state lasers.

High-frequency EPR of Tb3+-doped KPb2Cl5 crystal

High-frequency electron paramagnetic resonance (EPR) spectra of the KPb2Cl5:Tb3+ crystal have been investigated. Three types of spectra were observed in the frequency range of 74–200 GHz. The most intensive spectrum with the resolved hyperfine structure corresponded to transitions between sublevels of the159Tb3+ ground quasi-doublet with the zero-field splitting (ZFS) close to 48 GHz. Experimental results were analyzed by the exchange charge model of the crystal field affecting terbium ions in low-symmetry Pb2+ positions with the chlorine sevenfold coordination and the charge compensating vacancy in the nearest potassium site. The calculated values ofg-factors and ZFS were in agreement with the experimental data. The nature of a broad EPR line with ZFS of about 180 GHz and of additional weak EPR lines observed as satellites of the main Tb3+ lines was discussed.

High-beam quality, high-efficiency laser based on fiber with heavily Yb(3+)-doped phosphate core and silica cladding.

We have fabricated and tested a composite fiber with an Yb(3+)-doped phosphate glass core and silica cladding. Oscillation with a slope efficiency of 74% was achieved using core pumping at 976 nm with fiber lengths of 48-90 mm in a simple laser configuration, where the cavity was formed by a high-reflectivity Bragg grating and the cleaved fiber end. The measured M(2) factors were as low as 1.05-1.22 even though the fiber was multimode at the lasing wavelength.

Preparation of Pr- and Dy-Doped Rb1 − xMxPb2Cl5 − yBry (M = K, Cs) crystals

We have demonstrated for the first time the possibility of preparing high-purity and praseodymium- and dysprosium-doped solid solutions based on lead halides and alkali metals: Rb1 − xCsxPb2Cl5, Rb1 − xCsxPb2Br5, Rb1 − xKxPb2Cl5, and RbPb2Cl5 − yBry. According to X-ray diffraction data, Rb1 − xCsxPb2Cl5 and Rb1 − xCsxPb2Br5 crystals in the solid solution range are isostructural with the constituent double salts RbPb2Cl5 and RbPb2Br5, respectively. The double salt Rb0.5K0.5Pb2Cl5 is isostructural with KPb2Cl5, and the double mixed salt RbPb2Cl2.5Br2.5 is isostructural with RbPb2Br5. The Pr3+ and Dy3+ concentrations in crystals of the solid solutions and mixed salts were determined by inductively coupled plasma mass spectrometry (ICP-MS). In the Rb1 − x (Cs, K)xPb2Hal5 (Hal = Cl, Br) solid solutions, the dopants were observed to be nonuniformly distributed over the host. According to ICP-MS analysis data and absorption spectra, the Pr3+ and Dy3+ concentrations in the RbPbCl2.5Br2.5 crystals were higher than those in RbPb2Br5.

MIR spectroscopy of Tb3+-doped low phonon crystals and polycrystalline fibers

Spectroscopic investigations of Tb doped KPb2Cl5 and CsCdBr3 crystals and AgBr1-xIx polycrystalline fibers were carried out. Luminescence in 4.3-5.5 micrometers region was found in the KPb2Cl5:Tb3+ and CsCdBr3:Tb3+ crystals at room temperature. The AgBr1-xIx:Tb3+ polycrystalline fiber is expected to have luminescence in 3- 10 μm region. Gain properties of the crystals are evaluated.

The middle IR luminescence of Tb/sup 3+/-doped AgBr/sub 1-x/I/sub x/ polycrystalline fiber

Summary form only given. Tb/sup 3+/-doped silver halide crystals are promising candidates for a bright MIR source. It is predicted that its extremely narrow phonon band (<200 cm/sup -1/) does not quench emission transitions between energy levels of the f-electrons shape of the Tb/sup 3+/ ion up to as the low photon energy as one corresponding to maximum of room temperature heat emission. Besides the energy level scheme of the Tb/sup 3+/ ion is suitable for low cost Tm/sup 3+/ and Er/sup 3+/ lasers pumping at 2.0 and 2.8 /spl mu/m correspondingly. Finally a polycrystalline fiber could be drawn from the AgBr/sub 1-x/I/sub x/ crystal. This eliminates problems connecting with low f-f transitions cross sections of the Tb/sup 3+/ ion in MIR.

Singlemode crystalline fibers for the middle infrared

Microstructured and step-index fibers from silver halides singlemode at 10.6 mum and 5.5 mum are demonstrated. Experimental and theoretical evidences are presented to establish that the step-index fibers are singlemode at 10.6 mum.

New laser transition in a Pr{sup 3+}:RbPb{sub 2}Cl{sub 5} crystal in the 2.3-2.5-{mu}m range

Lasing at the 3F3 — 3H5 transition of the Pr3+ ion in a nonhygroscopic Pr3+:RbPb2Cl5 crystal is obtained for the first time at room temperature and the luminescent and lasing properties of the crystal are studied. The maximum differential cross section for stimulated emission in the 2.31—2.59-μm band of the 3F3 — 3H5 transition is found to be 1.7×10-19 cm2 and the lifetime of the 3F3 upper laser level is 0.11 ms.