Ninel V. Lichkova

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.

Single-mode microstructured optical fiber for the middle infrared

Microstructured crystalline optical fiber from silver halides is described. Both experimental and theoretical evidences are presented to establish that the fiber is effectively single mode at wavelength 10.6 micro m with numerical aperture NA=0.16 and optical losses of approximately 2 dB/m. Crystalline microstructured optical fibers offer key advantages over step-index optical fibers from silver halide crystals. The wide transmission range of wavelengths 2-20 micro m provides great potential for applications in spectroscopy and for the development of a range of new crystalline-based nonlinear optical fibers.

Crystalline silver halide fibers with optical losses lower than 50 dB/km in broad IR region and their applications

For the first time crystalline silver halide optical fibers with optical losses lower than 50 dB/km in a broad IR region from 9 to 14 micrometers were fabricated by an extrusion process. The optical loss mechanism essential to the lowest absorption in silver halide materials and fibers, namely intraband absorption by free holes in the valence band is proposed. The crystalline fibers with Rayleigh-type (lambda) (superscript -4) optical scattering were obtained. An IR region near 13 micrometers in AgBrI fibers with optical losses of less than 10 dB/km was discovered. Non-aged, stable IR polycrystalline silver halide optical fiber cables with losses lower than 1 dB/m in the region from 3 to 20 micrometers are demonstrated. Various applications of the developed low- loss silver halide fibers in remote spectroscopic chemical sensing, non-contact temperature monitoring and IR laser power delivery are discussed.

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.

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.

Up-Conversion Processes Accompanying the 2.5 μm Oscillation in the RbPb 2 Cl 5 :Pr 3+ Crystal

Up-conversion processes detrimental to oscillation on the 3F3 - 3H5 transition in RbPb2Cl5:Pr3+ crystal is investigated in order to optimize the dopant ions concentration and the pump wavelength.

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.

Crystalline silver halide fibers with optical losses lower than 50 dB/km in broad IR region

For the first time crystalline silver halides optical fibers with optical losses lower than 50 dB/km in broad region from 9 to 14 micron were fabricated by an extrusion process. The optical loss mechanism essential to lowest absorption in silver halides materials and fibers as intraband absorption by free holes in valence band are proposed. The crystalline fibers with Rayleigh type (lambda) -4 optical scattering were obtained. The IR region near 13 micron in AgBrI fibers with optical losses less than 10 dB/km was discovered. Non aged, stable IR polycrystalline silver halides optical fiber cables with losses, lower than 1 dB/m in region from 3 to 20 microns are presented. Various applications of developed ATR and reflection remote FTIR sensors, based on low losses silver halides fibers are discussed.