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This study introduces a method to predict the refractive index (RI) of nanocomposites with the Finite Elements Analysis (FEA) based on the Fabry-Perot interference. The efficacy was verified by comparing the estimated composites’ RI with the available data in the literature. In the experimental verification, the FEA-based prediction showed closer results with the measurement as compared to the effective medium approximation (EMA) approaches, which are prevalently used to predict the physical properties of nanocomposites. Due to the modeling capability, the FEA-method could investigate the effect of the nanoparticle morphology (particle size, shape, and orientation) and distribution. Large particle size, particle agglomeration in high electric-field amplitude region, and particle elongation along the light oscillating direction are found to be the major factors to enhance the RI of composites. The underlying mechanism of RI changing is attributed to the light scattering by embedded nanoparticles, which provides one potential real-time RI tuning schematic.

Arsenic selenide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength regions associated with residual hydrogen and oxygen related impurities, despite using 6N purified elemental precursors. Consequently, special additives and refined processing steps are utilized in an attempt to reduce these and other impurities. We investigate the formation of particulate impurities during a purification process based on the addition of 0.1 wt% elemental aluminum (Al) and 0.2 wt% tellurium tetrachloride (TeCl 4 ) during glass synthesis. It was found that during purification and melting steps, Al reacts with TeCl 4 to form AlCl 3 , which in turn reacts with oxygen and hydrogen impurities and the fused quartz (SiO 2 ) ampoule to produce HCl and stable submicron Al 2 SiO 5 compounds in the As-Se glass and fibers. The intensity of the H-Se absorption band centered at 4.57 μm has been significantly reduced from 18 dB/m to 0.8 dB/m. Using thermodynamic data, we have identified stable Al 2 SiO 5 submicron inclusions in the glass and fibers. A two-step gettering process is proposed as a solution to eliminating these inclusions.

In order to mimic and enhance the properties of moth eye-like materials, nanopatterned fused silica was chemically modified to produce self-cleaning substrates that have anti-reflective and infrared transmissive properties. The characteristics of these substrates were evaluated before and after chemical modification. Furthermore, their properties were compared to fused silica that was devoid of surface features. The chemical modification imparted superhydrophobic character to the substrates, as demonstrated by the average water contact angles which exceeded 170°. Finally, optical analysis of the substrates revealed that the infrared transmission capabilities of the fused silica substrates (nanopatterned to have moth eye on one side) were superior to those of the regular fused silica substrates within the visible and near-infrared region of the light spectrum, with transmission values of 95% versus 92%, respectively. The superior transmission properties of the fused silica moth eye were virtually unchanged following chemical modification.

The chalcogen glasses (i.e., glasses based on the elements S, Se, and Te) are transparent in the infrared (IR), possess low phonon energies, are chemically durable, and can be drawn into fiber. We review our recent research progress at the Naval Research Laboratory (NRL) to develop chalcogenide glass fibers for applications in the mid- and long-wave IR wavelength regions from 2 to 12 μm. Our recent effort in the development of low loss chalcogenide fibers, by describing the synthesis and purification methods, fiber drawing techniques, and highlighting the best results, is summarized. Various applications of these high quality chalcogenide fibers, including multimode beam combiners, mid-infrared supercontinuum sources, fiber Bragg gratings, fiber bundles for IR imaging, anti-reflecting surface structures, and modal filters, are described. Novel infrared (IR) lenses that enable a reduction in the size and weight of IR imaging optics through the use of layered glass structures with broad IR transmission are also presented.

Organically modified chalcogenide (ORMOCHALC) polymers have proven to be alternatives to the conventional inorganic materials for mid-wavelength infrared (MWIR, λ = 3–5 μm) optical components. While the refractive index of ORMOCHALC can be reinforced by the content of chalcogenides such as sulfur (S) and selenium (Se), the increased portion of the S or Se deteriorate the thermomechanical stabilities. As a remedy, this study utilizes ZnS nanoparticles to reinforce both optical and thermomechanical properties of the sulfur-based ORMOCHALC polymer, poly(S-random-1,3-diisopropenylbenzene). The refractive index n and extinction coefficient k of the nanocomposites were characterized by Infrared Variable Angle Spectroscopic Ellipsometry (IR-VASE). The results show a significant increment in the refractive index of Δn = 6.58% at the wavelength of 4 μm by adding 20 wt% ZnS (or 7.29 vol%) in the ORMOCHALC polymer. The low extinction coefficient of the nanocomposites (

The design and assembly of a unique infrared (IR) optical-fiber combined quantum cascade laser (QCL) system is described. This system integrates the output from four individual QCL modules, using infrared optical fibers, into a single output aperture to provide continuous spectral scanning from 6.02 to 11.17 µm. Spectra were collected on a diffuse gold reference as well as multiple concentrations of the explosive 1,3,5-Trinitro-1,3,5-triazinane (RDX) which were inkjet printed on aluminum substrates. The collected RDX spectra were compared to RDX spectra collected using a conventional Fourier-transform infrared spectrometer (FTIR). The results show good agreement between the spectra collected using the fiber-combined QCL system and the standard FTIR. These results demonstrate that the use of infrared optical fibers to combine multiple QCL modules is a viable approach to developing IR laser sources for use in fieldable devices capable of standoff detection of explosives.

The elucidation of the heat shock response (HSR) as a mediator of cellular stress has created a framework for understanding how these processes may promote tumorigenesis. Furthermore, the identification of specific components of the HSR and how they are co-opted by cancer cells has led to the discovery of new therapeutic targets. A wide range of small molecule inhibitors of the HSR are in various stages of development for clinical application in patients with cancer. The introduction of these novel small molecule inhibitors offers the opportunity for synergy with existing therapies and the potential for highly targeted treatments.

The present work demonstrates that high pressures alone can initiate and drive densification in nanopowder magnesium aluminate compacts without the application of temperature. The high-pressure processed nanostructured ceramic has a Vickers hardness of 182 and transmits in the infrared and visible wavelengths. The lack of externally applied thermal energy during densification enables the exploration of room temperature diffusion processes confined to nanoparticle surfaces that result in a bulk ceramics with grain sizes equal to the powder particle size.

Successful analysis of particulate/low vapor pressure analytes such as explosives and toxic chemicals, and commercial pesticides require new sampling tools that enable detection of these analytes using current vapor phase detection instruments. We describe a sampling approach that uses stainless steel screens coated with a sticky polydimethyl siloxane (PDMS) coating to capture particulates from surfaces. Preliminary results for the collection of dimethyl methylphosphonate (DMMP) sorbed onto silica gel (SG) particulates (DMMP/SG) from a surface with subsequent analysis by thermal desorption-cylindrical ion trap mass spectrometry (TD-CITMS) are reported.

Recently, 100 KW output power from YAG ceramic laser system has been demonstrated. It is a remarkable achievement considering that only a few milli-watt power was observed from the ceramic laser materials when first reported in the 1960s. This great improvement is mainly due to the success in high purity powder synthesis, development in new sintering technology and novel ideas in optics and device design. Additional developments have included highly doped microchip lasers, ultrashort pulse lasers, novel materials such as sesquioxides, fluoride ceramic lasers, selenide ceramic lasers in the 2–3 μm region, composite ceramic lasers for better thermal management, and single crystal lasers derived from polycrystalline ceramics. In this paper, we highlight some of these notable milestones and achievements and forecast the future in polycrystalline ceramic laser materials.

Specialized centers have reduced the adverse outcomes associated with esophagectomy in the last 2 decades and now report operative mortalities of less than 5%. With the expanding use of screening endoscopy, early invasive esophageal adenocarcinoma is diagnosed more commonly. As a result, more patients enjoy long-term survival after curative resection. Simultaneously, emerging evidence supports the equivalence of competing endoscopic therapies for treatment of very early cancers and benign diseases. Accordingly, surgical resection requires re-evaluation using enhanced parameters to enable more meaningful comparative outcome analyses. This article summarizes the current evidence and examines future directions regarding esophagectomy quality of life.

An all-fiber based supercontinuum source with emission covering the wavelength range of 1.9–4.8 μm is demonstrated. The laser source is based on a combination of silica commercial off-the shelf components and a chalcogenide-based nonlinear optical fiber. The system provides 10 dB spectral flatness from 2.0 to 4.6 μm, and −20 dBm points from 1.9 to 4.8 μm. The output power is 565 mW but scalable by scaling the repetition rate. The limit on the long wavelength edge of the system is identified as an extrinsic absorption feature in the fiber used; confirming the system could be scaled to generated a broadband source even further in the infrared.

By using a simple photodarkening model we investigate the dynamics of photodarkening in As 2 S 3 glasses under laser illumination. We find that, for illumination at 633 nm, the quantum efficiency of the photodarkening process is of about 4% and that the absorption cross-section of the dark centers is ∼2.2 times larger than that of the intrinsic structural units. The insights gained from the modeling are compared with the experimental results obtained when writing Bragg gratings using 633 nm, 594 nm and 568 nm laser light.

Tissue culture is one of the tools necessary for genetic engineering and many other breeding programs. Moreover, selection of high regenerating rice varieties is a pre-requisite for success in rice biotechnology. In this report we established a reproducible plant regeneration system through somatic embryogenesis. The explants used for regeneration were embryogenic calli derived from mature seeds cultured on callus induction media. For callus induction mature seeds were cultured on MS medium containing 30 g/l sucrose combined with 560 mg/l proline and 1.5-3.5 mg/l 2,4-D and 0.5-1.5 mg/l Kin. For plant regeneration, embryogenic calli were transferred to MS medium containing 30 g/l sucrose, supplemented with 1.0-3.0 mg/l BAP, 0.5-1.5 mg/l Kin and 0.5-1.5 mg/l NAA. The highest frequency of callus induction (44.4%) was observed on the MS medium supplemented with 2.5 mg/l 2,4-D, 0.5 mg/l Kin, 560 mg/l proline and 30 g/l sucrose. The highest frequency of shoot regeneration (42.5%) was observed on the MS medium supplemented with 2.0 mg/l BAP, 0.5 mg/l NAA and 0.5 mg/l Kin. The plantlets were hardened and transferred to soil in earthen pots. The developed method was highly reproducible. The in vitro developed plants showed normal growth and flowering under glasshouse conditions.

We report the first demonstration of laser oscillation at 1081 nm using a 10% Yb3+ doped Lu2O3 ceramic made by hot pressing of high purity co-precipitated powder. Approximately 2.5 W of output power was obtained with an optical-to-optical efficiency of ∼10%. This represents the highest output power obtained and the highest concentration of Yb3+ used thus far in a Yb3+ doped Lu2O3 ceramic.

We demonstrate that transparent magnesium aluminate spinel ceramic possesses excellent thermo-optical properties, a record low absorption loss of 6 ppm/cm, and superior ruggedness which position it as a prime candidate for an exit window aperture for high energy laser systems, especially in hostile environments. We also demonstrate lasing with an efficiency of about 45% in transparent Yb3+:Y2O3 ceramic made by hot pressing high purity submicron co-precipitated powder. This paves the way forward for high power solid state lasers exploiting hosts with higher thermal conductivity than YAG.

We demonstrate efficient generation of slow-light in As 2 S 3 single-mode fibers through stimulated Brillouin scattering using a 1548 nm DFB laser. Sinusoidal pulses with a 40-ns period have been delayed 19 ns with only 31 mW of launched power in 10 m of fiber.

We explored the possibility of using femtosecond laser pulses for fabricating gratings inside chalcogenide glasses. We demonstrate for the first time, to the best of our knowledge, gratings written inside bulk glasses and inside optical fibers using an 800 nm femtosecond laser. The fiber gratings are of great importance as they can be used as Bragg reflectors in the mid infrared region.

High purity chalcogenide glasses were prepared in the series As 2 S (3− x ) Se x where x = 0 to 3. The measured third order non-linearities increase with the value of x , and are up to about 1000 times larger than silica for As 2 Se 3 glass. We show that the anharmonic oscillator model, using the normalized photon energy, gives an excellent fit to the data over three orders of magnitude. Single mode optical fibers based on As 2 S 3 and As 2 Se 3 glasses have been fabricated using the double crucible technique and the Stimulated Brillouin Scattering (SBS) investigated. The threshold intensity for the SBS process was measured and used to estimate the Brillouin gain coefficient. Preliminary results indicate record high values for the figure of merit and theoretical gain, compared to silica, which bodes well for slow-light based applications in chalcogenide fibers.

In this study, we report the first measurements of wavelength and pulse length dependence of ablation thresholds in glassy As 2 Se 3 . Ablation yields, obtained from time-of-flight spectra were compared to laser intensity curves to obtain laser ablation thresholds. The wavelength dependence of the ablation thresholds were obtained by tuning the Vanderbilt–Keck free electron laser in the range of 3.2–5 μm. Pulse dependence of the ablation thresholds were obtained with a 5 μs macropulse in the wavelength range 3.2–5 μm and with macropulses ranging from 200 to 1000 ns at the wavelength of 3.5 μm. The wavelength dependence of the ablation threshold did not indicate that impurity absorption was a major factor in the ablation process in glassy As 2 Se 3 . The ablation threshold decreased with wavelengths corresponding to higher photon energies. In addition, a sharp increase in ablation threshold was observed with decrease in the macropulse length. Optical images of ablation craters at intensities above the threshold reveal significant melting on the sample surface. We will discuss the wavelength and pulse length dependence of the laser ablation threshold in glassy As 2 Se 3 in terms of a multi-photon process and a cumulative heating process.

Thin films of Er3+-doped gallium lanthanum sulfide (GLS) glass were prepared by RF magnetron sputtering onto fused silica and BK7 glass substrates. The films were characterized by use of SEM imaging, X-ray diffractometry, and energy dispersive spectroscopy. They are shown to be glassy, uniform in composition, and to exhibit an RMS surface roughness of

Scanning near-field optical microscopy (SNOM or NSOM) is the technique with the highest lateral optical resolution available today, while infrared (IR) spectroscopy has a high chemical specificity. Combining SNOM with a tunable IR source produces a unique tool, IR-SNOM, capable of imaging distributions of chemical species with a 100 nm spatial resolution. We present in this paper boron nitride (BN) thin film images, where IR-SNOM shows the distribution of hexagonal and cubic phases within the sample. Exciting potential applications in biophysics and medical sciences are illustrated with SNOM images of the distribution of different chemical species within cells. We present in this article images with resolutions of the order of λ/60 with SNOM working with infrared light. With our SNOM setup, we routinely get optical resolutions between 50 and 150 nm, regardless of the wavelength of the light used to illuminate the sample.

The electronic structure of two alkali tungsten tellurite glass series: (a) 10Li 2 O.xWO 3 .(90 - x)TeO 2 , and (b) xK 2 O.(10 - x)-Li 2 O.25WO 3 .65TeO 2 has been investigated by X-ray photoelectron spectroscopy. In contrast to alkali tellurite glasses, the core level spectra of the various elements appear unaffected when TeO 2 is replaced by WO 3 , with the alkali oxide concentration remaining constant. The Ols spectra do not indicate a clear separation of the bridging and non-bridging oxygen contributions. Thus we conclude that WO 3 behaves essentially as a network former in tellurite glasses. We have also obtained valence band spectra of the glasses and observed major changes with the addition of WO 3 In particular, the intensity corresponding to the lowest energy part of the spectra, attributed to the 02p bonding orbital, decreases significantly with increasing WO 3 , indicating the appearance of a new bonding configuration.

The advent of scanning near-field optical microscopy (SNOM) has augmented at a microscopic level the usefulness of optical spectroscopy in the region between 300 nm and 10 mum. Two-dimensional imaging of chemical constituents makes this a very attractive and powerful new approach. In this paper we show SNOM results obtained in several geometrical configurations on boron clusters in silicon, Li clusters embedded in a LiF sample and BN growth on silicon. We also show some results on the wavelength dependence of the reflectivity (R) in the near infrared (IR) of biological cells in liquid environment with the observation of the local fluorescence. The SNOM images revealed features that were not present in the corresponding shear-force (SF) images and which were due to localized changes in the bulk properties of the sample. The size of the smallest detected features clearly demonstrated that near-field conditions were reached both in the visible and infrared region. (C) 2004 Elsevier B.V. All rights reserved.

We show that integrin-linked kinase (ILK) stimulates the expression of VEGF by stimulating HIF-1alpha protein expression in a PKB/Akt- and mTOR/FRAP-dependent manner. In human prostate cancer cells, knockdown of ILK expression with siRNA, or inhibition of ILK activity, results in significant inhibition of HIF-1alpha and VEGF expression. In endothelial cells, VEGF stimulates ILK activity, and inhibition of ILK expression or activity results in the inhibition of VEGF-mediated endothelial cell migration, capillary formation in vitro, and angiogenesis in vivo. Inhibition of ILK activity also inhibits prostate tumor angiogenesis and suppresses tumor growth. These data demonstrate an important and essential role of ILK in two key aspects of tumor angiogenesis: VEGF expression by tumor cells and VEGF-stimulated blood vessel formation.

We have fabricated and characterized waveguides in thin films of Ge 5 As 34 Se 61 glass sputtered onto silicon wafer substrates. The 5-μm width waveguides were fabricated by exposure to 514.5 nm light from an Ar 3+ laser, with a lithographic exposure mask used to provide the lateral patterning for the waveguides. The measured losses of the waveguides ranged from 3.5 to 6.4 dB/cm. From SEM imaging, we concluded that scattering from microcracks at the glass–substrate interface was the dominant source of loss.

The infrared (IR) absorption of a biological system can potentially report on fundamentally important microchemical properties. For example, molecular IR profiles are known to change during increases in metabolic flux, protein phosphorylation, or proteolytic cleavage. However, practical implementation of intracellular IR imaging has been problematic because the diffraction limit of conventional infrared microscopy results in low spatial resolution. We have overcome this limitation by using an IR spectroscopic version of scanning near-field optical microscopy (SNOM), in conjunction with a tunable free-electron laser source. The results presented here clearly reveal different chemical constituents in thin films and biological cells. The space distribution of specific chemical species was obtained by taking SNOM images at IR wavelengths (lambda) corresponding to stretch absorption bands of common biochemical bonds, such as the amide bond. In our SNOM implementation, this chemical sensitivity is combined with a lateral resolution of 0.1 micro m ( approximately lambda/70), well below the diffraction limit of standard infrared microscopy. The potential applications of this approach touch virtually every aspect of the life sciences and medical research, as well as problems in materials science, chemistry, physics, and environmental research.

The strengths and Weibull parameters of chalcogenide As–S–Se and Ge–As–Se–Te glass fibers were measured, and the fiber fracture surfaces examined. The sulfide (As–S–Se) fibers have a mean strength of 545 MPa, characteristic strength of 567 MPa, and Weibull slope, m, of 8.5. The weaker telluride (Ge–As–Se–Te) fibers have a mean strength of 427 MPa, characteristic strength of 441 MPa, and a Weibull slope of 11. Fractographic analysis indicates the sources of failure in these glass fibers are inclusions, microbubbles and microcracks. Fracture mirror measurements enabled estimations of fracture toughness and mean critical flaw sizes. The lower strength of the Ge–As–Se–Te glass fibers was determined to be a consequence of a more severe flaw population.

Chalcogenide-glass fibers based on sulfide, selenide, telluride and their rare-earth-doped compositions are being actively pursued worldwide. Great strides have been made in reducing optical losses using improved chemical purification techniques, but further improvements are needed in both purification and fiberization technology to attain the theoretical optical losses. Despite this, chalcogenide-glass fibers are enabling numerous applications that include laser power delivery, chemical sensing, and imaging, scanning near field microscopy/spectroscopy, IR sources/lasers, amplifiers and optical switches.

Typically, Cu(In,Ga)Se2 (CIGS) thin films for photovoltaic devices are deposited by co-evaporation or, alternately, by deposition of the metals with or followed by treatment in a selenium environment. In this article, we describe CIGS films that are instead deposited by RF magnetron sputtering from a single quaternary target without any additional selenization. Devices built with these films exhibit efficiencies as high as 8.9%. We demonstrate that deposition power can be varied in order to change the film morphology and improve device performance.

Protein kinase B (PKB/Akt) is a regulator of cell survival and apoptosis. To become fully activated, PKB/Akt requires phosphorylation at two sites, threonine 308 and serine 473, in a phoshpatidylinositol (PI) 3-kinase-dependent manner. The kinase responsible for phosphorylation of threonine 308 is the PI 3-kinase-dependent kinase-1 (PDK-1), whereas phosphorylation of serine 473 has been suggested to be regulated by PKB/Akt autophosphorylation in a PDK-1-dependent manner. However, the integrin-linked kinase (ILK) has also been shown to regulate phosphorylation of serine 473 in a PI 3-kinase-dependent manner. Whether ILK phosphorylates this site directly or functions as an adapter molecule has been debated. We now show by in-gel kinase assay and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry that biochemically purified ILK can phosphorylate PKB/Akt directly. Co-immunoprecipitation analysis of cell extracts demonstrates that ILK can complex with PKB/Akt as well as PDK-1 and that ILK can disrupt PDK-1/PKB association. The amino acid residue serine 343 of ILK within the activation loop is required for kinase activity as well as for its interaction with PKB/Akt. Mutational analysis of ILK further shows a crucial role for arginine 211 of ILK within the phosphoinositide phospholipid binding domain in the regulation of PKB- serine 473 phosphorylation. A highly selective small molecule inhibitor of ILK activity also inhibits the ability of ILK to phosphorylate PKB/Aktin vitro and in intact cells. These data demonstrate that ILK is an important upstream kinase for the regulation of PKB/Akt.

The relative dielectric constant (e′), relative loss factor (e″), and loss tangent ( tan δ ) of the chalcogenide As40S(60 − x)Sex glasses (x=0, 20, 40, and 60 at.% Se) at room temperature have been investigated in the frequency range of 108–1010 Hz. Since the relative dielectric constant is related to polarization, the contribution of electronic and dipolar polarizations can be determined. As the Se content in the glass network increases, electronic polarization contributes up to approximately 78% of the relative dielectric constant for As40Se60 glass. This is mainly attributed to the larger electronic polarizability of the Se atom.

In this study we report first measurements of wavelength-selective infrared-induced materials modification of bulk As2S3 and As2Se3. These materials are currently being considered as candidate materials for infrared optical fiber transmission in the range of 1–10 μm. Our study is aimed at modifying oxygen, hydrogen and carbon impurities bound to chalcogenide constituent elements in the materials to reduce absorption. Tunable infrared radiation from the W.M. Keck Free Electron Laser (FEL) at Vanderbilt was used to excite specific vibrational modes, S–O–H and CHx modes in bulk As2S3 and Se–H, CHx and S–H2 modes in bulk As2Se3. Changes in vibrational mode amplitudes are monitored by measuring the intensity of the Fourier transform infrared (FTIR) spectra before and after irradiation at appropriate wavelengths. By tuning wavelengths to hydrogen vibrational modes, we find evidence that hydrogen is released and/or redistributed athermally. In particular, following irradiation at specific resonant wavelengths, vibrational mode amplitudes as monitored by FTIR associated with CHx are significantly reduced in bulk As2S3 and As2Se3 samples. In As2S3, the changes in CHx modes are reversed by heat treatment at 115°C for 35 min in nitrogen atmosphere.

Chalcogenide glass optical fibers were fabricated into functional apertured probes for near field scanning infrared microscopy. Probe fiber tips were chemically etched and aluminum coated for the purpose of simultaneously collecting near field shear force and optical signals. Surface topography and infrared optical reflectivity data were obtained using the tips in a scanning near field microscope while illuminating an integrated microcircuit with the output from a free electron laser operating at a λ of 4.7 μm. Approximately 25 nm topographical and 100 nm optical lateral resolution were observed.

We demonstrate the generation of fiber Bragg gratings in As2S3 fibers using a 633 nm HeNe laser and a 0/−1 phase mask. In a 20-micron core fiber, 17-dB reflection was observed at 1545 nm with a linewidth of 0.18 nm. This method is more robust than the transverse holographic method previously demonstrated in these fibers.

Glasses based on the composition Ge 16.5 As 18.5 Ga 0.5 Se 64.5 doped with Pr 3+ and Dy 3+ were investigated for active applications in the near and mid-IR. Pr 3+ has been investigated and mid-IR emission in the 3–5 μm region has been observed. Dynamic distillation and sublimation were performed on Se and As respectively to reduce the oxide and hydrogen related impurities in the glass. These techniques resulted in the elimination of oxide impurities and resulted in about a 10-fold reduction in hydrogen related impurities compared to the as-received chemicals. Spectroscopy performed on Dy 3+ resulted in a measured quantum efficiency for the 6 F 11/2 / 6 H 9/2 level of 94% with a branching ratio of 90% for the 1.3 μm transition and a calculated emission cross section ( σ e ) for this transition of 2.7 × 10 −20 cm 2 . Core only glass doped with 400 ppm Dy 3+ has been fiberized. The losses were 0.8 dB/m at 6 μm and 1.5 dB/m at 2.5 μm as measured by a cutback technique. Single mode Dy 3+ doped fiber has been drawn via double crucible techniques. The fiber had a 4 μm core with a 110 μm clad and had a core loss of 3 dB/m measured at 1.55 μm.

Amorphous GeS2 and Er3+:GeS2 gels have been fabricated. The Er3+ doped GeS2 gelation rate is quicker and goes more to completion than the corresponding GeS2 gel. This difference is attributed to the role of Er3+ as a Lewis acid which speeds up the thiolysis rate and, in analogy to silica gels, this rate leads to a gel with a particulate (10 nm) structure compared with a polymeric structure for the undoped GeS2 gel.

Chalcogenide glass fibers based on sulfide, selenide, telluride and their rare earth doped compositions are being actively investigated worldwide. Great strides have been made in reducing optical losses using improved chemical purification techniques, but further improvements are needed in both purification and fiberization technology to attain the theoretical optical losses. Despite these problems, current single mode and multimode chalcogenide glass fibers are enabling numerous applications. Some of these applications include laser power delivery, chemical sensing, imaging, scanning near field microscopy/spectroscopy, fiber IR sources/lasers, amplifiers and optical switches. The authors assert that the research and development of chalcogenide glasses will grow in the foreseeable future, especially with respect to improvements in the optical quality of the fibers and the performance of the fibers in existing and future applications.

HV- and HH-polarized Raman spectra of the chalcogenide glasses Ge 30 As 10 Se (60− x ) Te x (25⩽ x ⩽35) and the chalcohalide glasses Ge 30 As 10 Se 30 Te (30− y ) I y (0⩽ y ⩽30), Ge 30 As 10 Se 35 Te (25− z ) I z (0⩽ z ⩽20) were investigated. For the chalcogenide glasses, the main structural units include [AsSe 3− x Te x ] mixed pyramidal units, [GeSe 4− x Te x ] mixed tetrahedral units, and Ge–Te–Ge chains. The substitution of iodine for tellurium in the chalcohalide glasses results in the formation of Ge–I, As–I, and Se–I bonds which break up the three-dimensional network. The main structural units for the chalcohalide glasses are [AsSe x Te y I z ] mixed pyramidal units where x + y + z =3, [GeSe x Te y I z ] mixed tetrahedral units where x + y + z =4, and GeSe 3/2 I mixed tetrahedral units. The symmetry properties of these structural units has been determined through the dependence of the depolarization ratio on the frequency shift.

We have fabricated and tested infrared scanning near-field optical microscope (IR-SNOM) probe tips made from singlemode chalcogenide fiber. The process used to create the tips was similar to conventional micropipette-puller techniques, with some modifications to allow for the lower melting temperature and tensile strength of the chalcogenide fiber. SEM micrographs, showing tips with sub-micrometer physical dimensions, demonstrate the feasibility of this process. Topographical data obtained using a shear-force near-field microscope exhibits spatial resolution in the range 80-100 nm. Optical data in the infrared (near 3.5 mu m), using the probe tips in collection mode, indicates an optical spatial resolution approximately lambda/15. (C) 1999 Published by Elsevier Science B.V. hll rights reserved.

Thin films of barium copper sulfur fluoride (BCSF) doped with potassium were prepared by RF magnetron sputtering at a temperature of 100 °C. The morphology of the films was characterized with scanning electron microscopy and transmission electron microscopy. The phase of the films was determined by use of X-ray diffractometry and electron diffraction. It is shown that, unlike bulk BCSF and previously reported BCSF films, they exhibit a face-centered cubic structure with a lattice spacing of a = 6.27 A. The films are transparent from the visible to at least 30 μm, and they exhibit p-type room temperature conductivity as high as 187 S/cm.

Chalcogenide glasses are materials of interest for optical devices in the IR region. Of the As-based glasses, the As x S 1− x has received most of the attention, with a variety of processes and devices being studied and demonstrated. In the present work we explored the use of readily available 800-nm laser sources for fabricating surface gratings in As x Se 1− x glass. We demonstrate for the first time, to the best of our knowledge, surface relief gratings written using continuous-wave 800-nm laser light in AsSe. Such structures can be enhanced to enable short-period reflectors in AsSe-based waveguide and fiber devices.

A new method for fabricating microlenses in bulk, glassy Ge 20 Se 80 is demonstrated. Based upon a laser-induced thermal runaway effect, the process has been used to fabricate lenses with diameters between 70 and 180 μm and numerical apertures of about 0.4.

Varying substitutions of In2O3 for Ga2O3 in the BaOGa2O3GeO2 glasses were made and their effects on the glass transition temperature, density, hardness, chemical durability and the infrared transmission were studied. In2O3 substitution for Ga2O3, in general, resulted in improvement in the physical properties of these glasses. The glass transition temperature, density and hardness increased with the substitution. The chemical durability of these glasses improved with the substitutions and the infrared (IR) cut-off edge shifted to longer wavelengths. Phase separation was observed in compositions with higher In2O3 substitutions. The observed changes in physical properties and phase separation with In2O3 substitutions are explained on the basis of a structural model suggesting that octahedrally coordinated In3+ replaces tetrahedrally coordinated Ga3+ in the glass structure. The observed results are in good agreement with the model which also explains the phase separation observed at higher In2O3 substitutions.

We have fabricated unclad sulphide and telluride chalcogenide fibers with losses of 0.047 dB/m at 2.4 μm and 0.11 dB/m at 6.6 μm, respectively. Core/clad fibers with losses approaching 0.5 dB/m at 4.8 μm have been fabricated in long fiber lengths (~50 m). While theoretical minimum losses are estimated to be about 4 dB/km at around 5 μm for sulphide fibers, we have identified the absorption and scattering mechanisms which limit the practical losses. The bending strengths of these fibers have been measured and are satisfactory for short length applications. For longer lengths, both the loss and strength need to be improved.

The 78-kDa protein kinase Mekk1 plays an important role in the stress response pathway that involves the activation of downstream kinases Sek1 and stress-activated protein kinase/c-Jun NH2-terminal kinase. Conserved serine and threonine residues located between the kinase subdomains VII and VIII of many protein kinases are phosphorylated for maximal kinase activation. Two threonine residues within this region in Mekk1 at positions 560 and 572, but not the serine at 557, were shown to be essential for catalytic activity in this study. When these threonine residues were replaced with alanine, there was a significant loss in phosphotransferase activity toward the primary substrate, Sek1, and a large decrease in autophosphorylation activity. Site-directed mutagenesis demonstrated that these threonine residues cannot be replaced with either serine or glutamic acid for preservation of phosphotransferase activity. Further examination of the Mekk1 mutants isolated from 32P-labeled transfected COS cells showed that Thr-560 and Thr-572 were indeed phosphorylated after two-dimensional tryptic-chymotryptic phosphopeptide analysis. Additional determinants in the NH2-terminal domain of Mekk1 also play a role in the regulation of Mekk1 activity. Although Pak3 and PKC can activate Mekk1 in vivo, this interaction is indirect and independent, since there was no direct phosphorylation of Mekk1 by Pak3 or PKC or of Pak3 by PKC, respectively.

We present a model-independent measurement of B(D s − → Φπ − ) B(D 0 → K − π + ) by partially reconstructing the decay B 0 → D ∗+ D s ∗− . Using data collected with the CLEO II detector at CESR, we determine B(D s − → Φπ − ) B(D 0 → K − π + ) = 0.92 ± 0.20 (stat.) ± 0.11(syst.) . Our measurement of B ( D 0 → K − π + ) then gives B ( D s − → Φπ − ) = (3.59 ± 0.77 ± 0.48)%.

Using a sample of 3.1 fb−1 integrated luminosity accumulated with the CLEO II detector at the Cornell Electron Storage Ring, we measure the ratio of branching fractions β(D 0 → K − π + π 0 ) β(D 0 → K − gp + ) = 3.81 ± 0.07 ± 0.26 , the most precise determination of this quantity to date.

Using the CLEO II detector operating at the e + e − Cornell Electron Storage Ring (CESR), we present evidence for new decay modes of the Ξ c + into Ξ 0 π + , Ξ 0 π + π 0 , and Ξ 0 π + π − π + . The branching ratios of these decay modes, relative to Ξ c + → Ξ − π + π + , have been measured to be 0.55±0.13±0.09, 2.34±0.57±0.37, and 1.74±0.42±0.27, respectively.