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In this paper Ridge, S-bend waveguide design and analysis has been performed for C-band using various materials like Silica (SiO 2 ), Silicon Nitride (Si 3 N 4 ), Barium Fluoride (BaF 2 ) and Titanium Dioxide (TiO 2 ). We have performed a comparative study and identified Si 3 N 4 as the most suitable material for silicon photonics platform based on lower insertion and propagation losses. Si 3 N 4 based ridge waveguide reduces insertion loss to 5.68dB and propagation loss to less than 1dB/cm. These designed waveguides will be used in variable optical attenuator. Here in this paper, we also propose a variable optical attenuator based on the configurations of a Si 3 N 4 -BaF 2 and TiO 2 -Si 3 N 4 S-bend waveguides. The thermo-optic characteristics of Si 3 N 4 and BaF 2 materials are fully utilized for making variable optical attenuator (VOA). After performing software simulation, simulation results are verified with theoretical results. We get Optical attenuation of 1 to 50 dB with an applied electrical voltage of 0 to 20 V for length of 100 um device with low insertion loss.

Inorganic hollow spheres have a great potential in many fields, such as calcium phosphate (Ca3(PO4)2) as carriers of active ingredients and local delivery. They are typically synthesized by the methods that reply on template-based strategies. However, the template residue and energy consumption during template removal are drawbacks. Currently developed template-free methods remain challenges such as time, cost and complicated procedures. In this paper, we introduce a general low-cost and template-free precipitation method with simple procedure. A series of inorganic hollow spheres, including calcium phosphate, calcium fluoride, strontium phosphate, strontium fluoride, barium phosphate and barium fluoride via magnesium were successfully synthesized, respectively. Based on these experimental results, a new model is proposed to explain the mechanism of the hollow inorganic spheres formation. This paper provides a general method to synthesize inorganic hollow spheres, which may have an important indication to other systems.

The Near InfraRed Camera (NIRCam) for the James Webb Space Telescope (JWST) is a refracting instrument. Its unique optical performance derives from the Lithium Fluoride, Barium Fluoride and Zinc Selenide lenses that provide aberration and color correction over the large operating wavelengths, 0.6-5 microns. This paper describes cryogenic test results of the mounted camera lenses in a flight-like configuration. These data, which evaluate the foundation for NIRCam optical performance, reveals design strengths and challenges. This is a follow-up paper from SPIE paper 590409 (1) which presented the initial camera lens design.

For the measurement at extremely high interaction rates with fast scintillators, pile-up of consecutive events is a limiting factor. With a decay time of 600 ps of the fast crossluminescence component, Barium Fluoride (BaF2) is one of the fastest inorganic scintillators known today. However, the dominating slow component with a 3 orders of magnitude longer decay time of 630 ns limits the rate capability. To circumvent this limit, different approaches have been made in the past. The slow component can be suppressed for example by doping the crystals with rare earth ions like La3+. The paper will give an overview over the various concepts investigated in the past and present the suppression via optical band pass filters. This method has been chosen for the upgrade of the BaF2 crystals in the most forward region of the TAPS-spectrometer at ELSA in Bonn. It allows to reuse the existing crystals and to achieve a high degree of suppression of the slow component. The focus of the paper will be on the selection of the filters, the achievable rate capability and the energy resolution of the fast component.

Because of their ultrafast scintillation with subnanosecond decay time, barium fluoride (BaF2) crystals have attracted broad interest in the high energy physics and nuclear physics communities. One crucial issue, however, is its slow scintillation component with 600-ns decay time, which causes pile-up in a high rate environment. Previous studies show that the slow component can be suppressed effectively by rare earth doping. In this paper, we report investigations on a set of $\Phi \,\,18\times21$ mm3 BaF2 cylinders doped with different yttrium levels grown at Beijing Glass Research Institute (BGRI), from which the optimized yttrium doping level was determined. $\text{A}\Phi \,\,40\times160$ mm3 BaF2 ingot with 5 atomic % (at.%) yttrium doping was consequently grown at BGRI and was used to cut one $25\times 25\times100$ mm3 crystal and several thin slices. Their optical and scintillation properties were measured at Caltech. The results show that yttrium doping effectively suppresses the slow component while maintaining its ultrafast light unchanged. Research and development will continue to develop large-size BaF2:Y crystals with improved optical quality for a fast BaF2:Y crystal calorimeter for Mu2e-II.

Positron annihilation lifetime (PAL) spectroscopy is widely used in the characterization of material microstructures. It has a very high sensitivity to the material defects. This paper describes how we developed a digital PAL spectrometer with two barium fluoride (Ba F 2 ) detectors and reading the data with a fast digital oscilloscope. We achieved better time performance for the digital PAL spectrometer using a multi-parameter discrimination method and various pulse smoothing algorithms. With two Ba F 2 detectors in the coincidence mode, we achieved a time resolution of 160 ps for 0.511 MeV annihilation gamma rays. The multi-parameter discrimination method implemented can remove incorrect events more effectively than the conventional energy discrimination method. With this enhancement in event discrimination, the digital PAL spectrometer’s time performance has improved, which results in more accurate PAL characterization. In a lifetime measurement, the PAL spectrometer’s time resolution is about 130 ps, which is much better than most PAL spectrometers. With the multi-parameter discrimination method, the resolution component from the incorrect events decreases drastically, and the leading edge distortion of the PAL spectrum is significantly improved.

Barium fluoride (BaF2) crystal has a fast scintillation light peaked at 195 and 220 nm with a sub-ns decay time. This ultrafast scintillation promises a wide application in an area where extreme fast timing is important, such as future high-energy physics experiments, gigahertz hard X-ray imaging, and time-of-flight positron emission tomography. BaF2 crystal, however, has also a slow scintillation component peaked at 310 nm with a decay time of about 600 ns, which causes pileup. Suppression of the slow scintillation component by selective doping, such as Ce, La, Tm, and Y, was discussed 20 years ago. In this paper, we report suppression of the slow component in BaF2 crystals by yttrium doping. Single crystals with 1 at% Y doping were grown by vacuum Bridgman technique at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China. Their radioluminescence, optical transmittance, light output, fast/slow ratio, decay kinetics, and light response uniformity were measured. The results show that 1 at% Y doping suppresses the slow scintillation component in BaF2 crystals by a factor of 6, while the fast component remains unaffected.

Inorganic materials with short radiative decay time are highly desirable for fast optical sensors. This paper reports fast photoluminescence (PL) from a series of barium hexafluorosilicate (BaSiF6) superlong nanowires with high aspect ratios, codoped with Ce3+/Tb3+/Eu3+ ions, with a subnanosecond decay time. Solvothermally synthesized BaSiF6 nanowires exhibit a uniform morphology, with an average diameter less than 40 nm and aspect ratios of over several hundreds, grown in the c-axis direction with {110} surfaces. The PL emission from the codoped BaSiF6 nanowires, when excited by a 254 nm source, is dependent on Tb3+ concentration, and the energy transfer from Ce3+ to Tb3+ and to Eu3+ ions allows efficient emissions in the visible spectra when excited by a near UV source. Annealing BaSiF6 nanowires at 600 °C in a vacuum produced barium fluoride (BaF2) nanowires composed of nanocrystals. Both BaSiF6 and BaF2 nanowires exhibit fast emissions in the visible spectra, with enhanced intensities compared with their codoped microparticle counterparts. The decay time of codoped BaSiF6 nanowires is found to be shorter than that of codoped BaF2 nanowires. The energy transfer is also observed in their cathodoluminescence spectra with high-energy irradiation.

This paper describes the study of the surface morphology of BaF2 epitaxial films grown by means of molecular beam epitaxy in various growth regimes on a CaF2/Si(100) surface, which is performed by means of atomic force microscopy. The CaF2 layers were obtained on a Si(100) substrate in a low-temperature growth regime (T s = 500 °C). The technological regimes of growth of BaF2 continuous films with a smooth surface on CaF2/Si(100), suitable as buffer layers for the subsequent growth of PbSnTe layers or other semiconductors, such as A4B6, and solid solutions based on them.

Single-point diamond turning is a high-efficiency, low-cost method for manufacturing harmonic diffractive optical elements (HDOEs). Generally, in order to ensure high diffraction efficiency of HDOEs, a half-round tool is used to reduce surface-relief profile errors and a super small feed rate is selected to control surface roughness when hard-brittle materials are turning. However, this method is no longer suitable for soft-brittle materials, which have a strict requirement for the range of the feed rate. It limits the types of materials available for HDOEs. Therefore, according to the range of the feed rate and the cutting depth for soft-brittle materials, an optimized turning model is proposed in this paper. It overcomes the high surface roughness caused by the half-round tool; meanwhile, the advantage of the half-round tool is kept in terms of surface-relief profile errors. On this basis, a mathematical model is proposed to reveal the relationship among diffraction efficiency, period widths, tool radius, and feed rate with different soft-brittle optical materials. As a typical soft-brittle material, barium fluoride ( B a F 2 ) was selected to be the material for manufacturing HDOEs. By using the optimized model, the turning experiment of B a F 2 HDOEs was completed, and then the B a F 2 HDOEs with R a = 2.75 n m were obtained. The optimized model is verified to be effective and further provides theory guidance and engineering application in the optical manufactory field of soft-brittle materials for HDOEs. The range of application materials for HDOEs is enriched, and the freedom of advanced optical design is broadened.

This paper reports optical absorption spectra and rapidly decaying luminescence of BaF2 crystals measured at 295 K under excitation pulse of accelerated electrons and excited simultaneous stimulated emission of CdSe crystal. It is shown that the simultaneous excitation of the crystals BaF2 pulse accelerated and SE semiconductors in electronic components STE absorption leads to a reduction efficiency of creation of STE and the appearance of fast decaying emission in the UV region of the spectrum.

Phase formation in the BaF 2 -CeF 3 system has been studied in the aqueous nitrate media by co-precipitation technique with the use of HF and NH 4 F as fluorinating agents. Formation and properties of fluorite-type Ba 1-x Ce x F 2+x (х = 0.32–0.58) and tysonite-type Ce 1-y Ba y F 3-y (y = 0–0.20) solid solutions are described in the present paper.

Our recent study was focused on the emission from Laser Induced Plasma (LIP) at the delay times of tenths of microseconds after the laser pulse. At these long delays, the spectrum is dominated by the broadband molecular emission and plasma induced luminescence (PIL) produced by a luminescent matrix; only solitary atomic emission lines can be seen. Barium fluoride BaF2 activated by thulium (Tm) is a famous scintillator that presents the promising object for LIP in terms of both the potential for BaF molecular emission and Tm3+ PIL. The detection of molecular and PIL bands presents a new opportunity for analysis of halogens and rare-earth elements, which are the difficult objects for LIBS. In this paper, we show that the UV, Green, Extreme Red, and Infrared molecular bands from BaF and blue luminescence from Tm3+ are present in the LIP emission spectra while the detection of atomic emission from F I and Tm I was impossible with the same experimental setup. Thus, the detection of molecular emission and PIL can be more sensitive than the traditional detection of emission from atoms and ions.

Gigahertz (GHz) hard X-ray imaging for the proposed MaRIE project presents an unprecedented challenge for the front imager in both speed and radiation hardness. We proposed two ultrafast inorganic-scintillator-based front imager concepts: a total absorption one and a multilayer one, and investigated optical and scintillation properties for a set of inorganic scintillators at the Caltech HEP crystal laboratory. The results show that yttrium doped barium fluoride crystals and gallium doped ZnO nano-particle-based films are promising for these two concepts, respectively. In this paper, we report their optical and scintillation property as well recent progresses on slow component suppressing in barium fluoride crystals by yttrium doping, and its radiation hardness.

Lead–gallium glasses, due to the absence of typical glass-forming components, are characterized by an increased tendency to crystallization. Despite this, they are interesting materials due to a shift of IR absorption edge up to 6–7 μm. The paper considers how the SiO2 dopant affects thermal stability and the UV–VIS and IR transmittance of lead-gallium glasses. The base lead-gallium glass (0.75PbO·0.25Ga2O3) was modified by the addition of 5, 10 and 15 mol% SiO2, respectively. DTA/DSC data showed that the glasses are characterized by the multi-stage crystallization, which is changed with the amount of silica doped. The XRD analysis confirmed that: (i) different forms of lead oxide crystallize after heat treatment of the glass, and (ii) the Ga2PbO4 phase is formed at higher temperatures. The silica admixture allowed inserting a few percent of BaF2 into the lead–gallium glass structure. It was found that a transparent glass–ceramic based on the lead-gallium glass with a low phonon barium fluoride phase can be obtained during the thermal treatment. The study of UV–VIS–IR transmittance shows that 10–15 mol% SiO2 in the lead-gallium glasses diminishes the absorption band in the range of 2.6–4 μm due to the presence of hydroxyl groups and simultaneously reduces transmittance in the range of 5–6.5 μm from 10 to 20%. Introduction of SiO2 to the glass results in the increase of transmittance in the shorter wavelength region and the UV-edge shift is observed. It was also confirmed that the BaF2 nanocrystallites exert s no effect on the transmittance of the spectrum analyzed.

The paper summarizes experimental evidence of anomalous luminescence in RE-doped dielectric materials. Special attention is paid to Pr 3+ -doped LiNbO 3 and LiTaO 3 , and Eu 2+ -doped XF 2, where X = Ba, Sr. Luminescence, luminescence excitation spectra and luminescence kinetics results are discussed obtained at ambient and high hydrostatic pressure at various temperatures. Hydrostatic pressure has been shown to cause a red shift of anomalous luminescence. The experimental data show the existence of temperature- and pressure-induced spectral transformation where anomalous luminescence is replaced with normal d–f emission in Eu 2+ centers. The model predicts strong electron-lattice coupling of bound excitons and relaxation in the system’s excited states, as well as the pressure effect of spectral transformation from anomalous to normal emission.

This paper reports on a study of cross-luminescence in barium fluoride crystals doped by a variety of impurities (K+, Cd2+, Y3+, Yb3+, La3+). It is shown that doping of the crystal with a trivalent impurity gives rise to the formation of an additional cross-luminescence band peaking at 7.5 eV, the intensity of this band increasing with increasing impurity concentration.

This paper presents both investigations of high-energy luminescence with maximum at 7.5 eV in BaF2:Y3+ and BaF2:Yb3+ crystals and theoretical calculations of cross-luminescence spectrum in crystals of barium fluoride with interstitial ions of fluorine. The dependencies of the 7.5 eV emission intensity as function of different impurities mol. concentration are presented. The intensity of this emission increases with concentration of rare-earth impurity, but in the case of doping by Yb3+ and Y3+ this intensity is less than that in the case of La3+ doping. This feature (as well as the nonlinear dependence) can be due to the creation of clusters, i.e., aggregation of impurity ions and F--interstitials. The intensity of the 7.5 eV luminescence in a BaF2:Y3+ crystal after annealing at 1000 K increased by three times but it remained less than in the case of La3+ doping. Theoretical calculations of the core hole electronic and spatial structure and cross-luminescence spectrum were performed in the [Ba6F12] cluster. This cluster contains interstitial ion of fluorine, which is surrounded by six ions of Ba2+. In the case of using Hartree-Fock method the calculated luminescence spectrum of BaF2 crystal with interstitial fluorine shows cross-luminescence band with main maximum at 5.2 eV and high-energy band at 11.7 eV. In the case of using TD DFT method the energies of both cross-luminescence transitions and of transition between interstitial ion and core levels are in satisfactory agreement with experimental data, being all overestimated by approximately the average value of 0.8 eV.

A large BaF 2 detector array along with its dedicated CAMAC electronics and VME based data acquisition system has been designed, constructed and installed successfully at VECC, Kolkata for studying high energy γ rays ( > 8 MeV ). The array consists of 162 detector elements. The detectors were fabricated from bare barium fluoride crystals (each measuring 35 cm in length and having cross-sectional area of 3.5 × 3.5 cm 2 ). The basic properties of the detectors (energy resolution, time resolution, efficiency, uniformity, fast to slow ratio, etc.) were studied exhaustively. Complete GEANT3 Monte Carlo simulations were performed to optimize the detector design and also to generate the response function. The detector system has been used successfully to measure high energy photons from 113 Sb, formed by bombarding 145 and 160 MeV 20 Ne beams on a 93 Nb target. The measured experimental spectra are in good agreement with those from a modified version of the statistical model code CASCADE. In this paper, we present the complete description of this detector array along with its in-beam performance.

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 er of single crystal BaF2 in the temperature range from 14 to 290 K at frequencies of 8, 10.4, 12.1, 17.6, 21.1 and 24.4 GHz. 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 (14 K) to 7.35 (290 K). The loss tangent increased from 1 × 10−5 to 1.1 × 10−4 over the measured temperature range, 14–290 K at a frequency of 10.4 GHz. The measured microwave properties show that BaF2 can be used in many microwave devices.

Coated-conductor applications of YBCO require YBCO layers with high J/sub c/ and a thickness of several micrometers. The barium fluoride process offers a convenient way of depositing crack-free fluorinated precursor layers up to 5 microns thick. However, converting thick precursor layers into c-axis-oriented YBCO films is challenging due to extensive nucleation of random grains. In this paper we address this problem with both a theoretical and experimental analysis of YBCO nucleation. We utilized optical polarization contrast to observe YBCO nuclei imbedded in the precursor matrix. We observed that the nuclei density strongly depends on processing parameters, with the oxygen partial pressure being one of the strongest factors. During ex-situ processing the nuclei merge and form grains and the nuclei density is, therefore, directly related to the grain size of YBCO film. It is desirable to have a small grain structure, since large grains do not connect well and the J/sub c/ of such a film is low. However, attempts to increase the nuclei density also generates more randomly oriented grains. Therefore the optimization of ex-situ processing is essentially finding a balance between c-axis grain density and random grain content.

Barium fluoride windows are commonly used in infrared microspectroscopy because of their good transmission and their nonhygroscopic characteristics. The latter feature is particularly useful for biological specimens. The difference in infrared focus from visible focus occurs particularly at low frequencies, due to differing indices of refraction at various wavelengths, causes experimental problems. The work described in this paper addresses this issue. One example of this is illustrated with recent studies of bone sections by microspectroscopy at small mask sizes that require working around this problem when estimating the contents of phosphate and carbonate which absorb at low frequencies. When using a single 2 mm thick BaF2 dispersive substrate it is necessary to adjust infrared focusing of the transmitted radiation onto the detector by maximizing the single beam response of the microspectrometer specifically for the band or bands being studied. At optimum infrared focus the projected image of the mask degrades in the visible view. Thus it was necessary to alternate between the visible focus for the image capture and the optimum infrared focus for scanning the spectrum. The problems and limitations imposed from dispersive substrates were summarized by Carr [3] where the focus shift response by wavelength was calculated for several common substrate materials. The relative transmission resulting from extreme focus shifts which ranged from 20 to 140 μm was determined specifically for a 2 mm thick BaF2 disk at various wavelengths. Of the various nondispersive infrared transmitting materials that exist, the experimentation presently reported involves diamond windows of different dimensions. Whereas the benefit of using a diamond or another substrate with minimal dispersion is obvious, the limitations of size, cost and interference fringes warrant consideration. Single beam spectra as well as spectra of specimens obtained with these alternatives illustrate their utility in solving the problem of dispersive windows in infrared microspectroscopy.

Open f-shell rare-earth (RE) ions in wide bandgap host materials are usually characterized by closely spaced electronic levels due to various electron configurations and charge states. These levels provide convenient luminescent transitions that can be excited by efficient recombination of charge carriers generated in the host material by ionizing radiation. Therefore, it is the area of ionizing radiation detectors, where search for new, fast and efficient scintillator materials for high-energy physics and nuclear medicine, has yielded much of the recent advances in the understanding of radioluminescence and scintillation mechanism in some solid state, UV and VUV luminescent, RE-activated materials. In this paper we shall present selected results of basic experiments such as radioluminescence, VUV spectroscopy, time profiles and thermoluminescence, on barium fluoride (activated with Ce, Pr, Nd, Tb) and two aluminum perovskites, YAlO3 and LuAlO3, activated with Ce. We shall demonstrate that these results point to consecutive carrier capture and recombination at RE ions as the basic mechanism of radioluminescence and scintillation in these materials, despite the strong self-trapping and poor charge transport properties. Consequently, various electron and/or hole traps that intercept and retain for some time the recombining charge carriers play an active role influencing both the scintillation light yield and time profiles of scintillation pulses in these and many other wide bandgap RE-activated luminescent materials.

ISSN 0967–9782 to metallic barium and other barium compounds, including barium oxide, hydroxide, peroxide, and a variety of salts. Barium compounds are used widely in industry and medical science ‘as loaders for paper, soap, rubber and linoleum, as drilling muds in oil rigs, in the manufacture of valves and in the production of lights and green flares .. . as pigments in the manufacture of paints; in cement where concrete is exposed to salt water; in the radio industry to capture the last traces of gases in vacuum tubes; in the ceramic and glass industries; as insecticides and rodenticides; as extinguishers for radium, uranium, and plutonium; and as contrast material in X-ray medical examination’.1 Barium sulphate is the source of most Ba compounds but barium carbonate 3 ) is used both in the ceramic industry and to make barium fluoride. It has sometimes been suggested that for use in pottery glazes, barium sulphate 4 ) should be substituted for 3 due to its lower solubility (Table 1).2 It should be remembered that the ultimate toxic agent is the barium ion, and so the relative toxicity of barium compounds is directly related to their ability to dissolve or form ions. This can cause problems with the burning off of the sulphur dioxide from the glaze during firing resulting in pinholing. In some cases the substitution may be satisfactory, and so the danger to the potter using the barium can be lessened, but it does not help the problem of barium leaching from glazes used on domestic ware and thus the danger to the user.

This paper describes the stabilizing effect of MgF2 on the binary system InF3–BaF2. A complete investigation of the In–Ba–Mg system led to samples up to 5 mm in thickness. Further optimization of this system was achieved by incorporation of other fluorides, resulting in increased resistance to devitrification. Thermal and optical data are reported.

The scanning soft X-ray microscope operating at Hasylab/Desy has been developed to combine lateral and temporal resolution, tunability and various conventional spectroscopy techniques. Different mirror optics are used to form a microprobe in the energy range 15–1500 eV. A grazing incidence ellipsoidal mirror provides a resolution of 1 μm over the entire energy range, and in the vacuum ultraviolet region below 30 eV, 0.15 μm can be achieved with a Pt-coated Schwarzschild objective. Due to the large working distance of the optics used, the detection and analysis of several surface signals are comparatively simple. Detectors and spectrometers for photoelectrons, luminescence, fluorescence, desorbed ions, reflected, scattered and transmitted light are built in permanently into the microscope. Furthermore, some combinations of the different methods can be used for simultaneous measurements. In this paper the technical developments of recent years are described. A short representation of some exemplary applications will give an insight into the work of our group and illustrate the characteristics of the microscope. The following topics are discussed: cross-luminescence of barium fluoride, visible luminescence and degradation of porous silicon, photoluminescence of ceramics, chemical contrast in photoemission spectroscopy, and Bragg reflection as a contrast mechanism in X-ray microscopy.

This paper describes a research program in which the goal is to alter the thermal expansion coefficient of a composite solid lubricant coating, PS300, by compositional tailoring. PS300 is a plasma sprayed coating consisting of chrome oxide, silver and barium fluoride/calcium fluoride eutectic in NiCr binder. By adjusting the composition, the thermal expansion coefficient can be altered, and hence chosen, to more closely match a selected substrate preventing coating spallation at extreme temperatures. Thermal expansion coefficients (CTE) for a variety of compositions were measured from 25 to 800 C using a commercial dilatometer. The CTE's ranged from 7.0 to 13 x lO(exp -6)/deg C depending on the binder content. Subsequent tribological testing of a modified composition indicated that friction and wear properties were relatively insensitive to compositional tailoring.

The goal of this paper is to investigate selected fluoride optical materials and to present a photonic crystal fiber designed for specific applications in dispersion compensation by using those materials. The idea how to restrict chromatic dispersion is to increase the index contrast by using calcium fluoride or barium fluoride in the first ring of holes, which lower the effective index. In general, fluoride materials compared to standard silica glass in many aspects offer better mechanical and optical properties. The use of fluorides allows achieving broadband dispersion suppression impossible to achieve in standard fibers with similar geometry. The presented result comprises a numerical model of a photonic crystal fiber in a submicron lattice, specific for its negative dispersion coefficient achieved for broad spectrum of telecommunication wavelengths, i.e. 1300 – 1700 nm. The core consists of pure silica surrounded by three doped regions and three air-holes. Holes doped with fluoride materials enhance negative dispersion coefficient to -438 ps.nm -1 .km -1 . The diameter of doped regions is about 1 micrometer. Simulations were done by using the full-vector FDFD method. The wavelength evolution of refractive index of materials was introduced by using the Sellmeier approximation. The major advantage of the designed fibers is their material composition, low attenuation and broadband utilization.

Containerless fabrication of fluoride glass rods using the gas film levitation technique has been developed to overcome some of the present limitations in the classical preparation by melt routes, namely (i) crucible interaction and associated contamination (platinum particles, chemical reactions) and (ii) mould interaction (mechanical stresses, surface defects). Further, the shaping ability of this technique allows the preparation of rod-like preforms for subsequent fibre drawing. Previous results have shown the ability of the technique to directly prepare test samples (discs) around 6 g in weight having Rayleigh light scattering losses near the intrinsic minimum values. In this paper, the preparation of fluoride glass rods (ZBLAN) by the gas film levitation technique is described and preliminary results on light scattering of glass rods thus prepared are presented. Present levitators are designed to process glass rods up to 50 g in weight in a batch process. An advanced levitation configuration, being developed to prepare long rods using a continuous replenishment process, is briefly presented.

The suitability of barium fluoride (BaF2) as an internal reflection element for ir-ATR spectroelectrochemistry has been examined in this paper. Thin gold or platinum electrodes have been sputtered onto a hemispherical BaF2ir transparent crystal and the ir spectra of a third (air or water) medium were obtained at a number of different angles of incidence. These results have then been compared with theoretical results calculated via the Fresnel formulae. In general, good agreement between the theoretical and experimental results was obtained. In the case of platinum electrodes, the predicted desirable properties could not be experimentally realized due to the poor adhesion of Pt upon BaF2 in an aqueous environment. It is shown in this work that the BaF2 + Au ATR system is very useful for use in ir spectroelectrochemistry for a number of reasons, in particular due to the posibility of using relatively thick (30 nm) electrode layers and also because of the high reflected light intensity inherent in the system (minimizing noise effects.)

H center, a hole trapped at an interstitial anion site, placed on the 111 surface of Barium fluoride BaF2 has been studied by using density functional theory DFT with hybrid exchange potentials, namely, DFT-B3PW. Two different configurations of surface H center are investigated carefully. Both surface H-center systems have strong relaxations because of the surface effect. In the configuration that the interstitial fluorine atom is within the surface, named case 1 in this paper, the unpaired electron is almost equally distributed onto the two atoms of the H center, which is quite different from the bulk H-center case. The other configuration with one of the F atoms of the H center located above the BaF2 111 surface case 0 has a more polarized charge distribution as compared to that obtained in the bulk case and case 1. The calculation on total energies of different surface H-center configurations implies that H centers have a trend to locate near the surface. The creation of a surface H center in BaF2 results in a new -hole band located at the point 3.99 and 2.70 eV, for the cases 0 and 1, respectively, above the top of valence bands. According to our calculations on density of states, the constituents of the defect bands are cleared and the -hole band is primarily composed of pz orbitals localized on the H center.

The paper is focused on numerical analysis of lasing in blue and yellow spectral range of a Dy:ZBLAN fiber laser system, working in a Fabry-Perot configuration. A mathematical model based on measured spectroscopic data, as well as fiber structural parameters is implemented and yielded results are confronted with available experimental data. A reasonable agreement is found despite relative simplicity of the proposed solution.

The Near InfraRed Camera (NIRCam) for the James Webb Space Telescope (JWST) is a refracting camera system. Its unique performance derives from the Lithium Fluoride, Barium Fluoride and Zinc Selenide lenses that provide aberration and color correction over the large operating wavelength. This paper describes the optical prescription, lens materials and prototype characterization for the camera lenses.

In this paper, new results about a transient femtosecond index grating in barium fluoride has been presented. There is a strong indication that the lifetime of the grating is only limited by the pulse width of the laser. Additionally, it is shown how the transient grating promotes highly efficient third-harmonic generation and diffraction due to a self phase matching mechanism. The immediate build-up and decay opens the way to an application as a femtosecond switching device.

With the number of cerium doped radiation resistant glasses available to the designer of space optics rapidly decreasing, it iscritical to identify and characterize all potential sources of radiation resistant glasses and crystals. Unfortunately much of thedata on radiation testing of glasses is quite old and often not completed at very high dose rates as might be experienced by anunshielded space optic in orbit for many years. In addition, many optical glasses and crystals are manufactured today withmuch higher purity than in the past in order to increase their ultraviolet transmission properties. Consequently these glassesare much more resistant to space radiation than in the past. In this paper we will present gamma radiation effects on thetransmission properties of today’s fused silica, sapphire, calcium fluoride, barium fluoride, Schott cerium doped radiationresistant glasses, Schott colored glass filters, as well as some infrared glasses with up to a 10 Mrad dose.Keywords: Space radiation, radiation resistant glasses, crystals, space optics

Interference of two non-collinear femtosecond laser pulses induces, due to the optical Kerr effect, a refractive index grating in a thin slide of barium fluoride crystal. Self diffraction and diffraction of the third harmonic of the incident light, generated within the slide, is observed to several orders with an efficiency of better than 10 %. The intensity of the third harmonic is so high that for several diffraction orders the fluorescence of a white paper screen is easily visible to the naked eye. All effects are only present upon coincidence of both incident pulses, showing their instantaneous nature.

Different impurities influence the radiation damage of barium fluoride (BaF2 )crystal in different ways. Stable metal elements, such as alkali elements and alkali earth elements, have no effect on the radiation resistance. Most transtion metal elements areharmful to the radiation resistance. There are three kinds of effects of rare earth elements. Stable trivalence elements, such as Y, La and Lu, have no effect on the radiation resistance, while the elements which changes its valence from +3 to +4 under irradiation, such as Ce and Pr, are harmful. The elements which changes its valence from +3 to +2 underirradiation, such as Sm,Eu,Dy and Yb, are useful in eliminating color centers in visible range. Oxygen and hydroxyl ions which were introduced into the crystal from the raw material of BaF2 or a low vacuum during crystal growing are very harmful to the radiation resistance. The formation of “Complex Color Centers” is considered as the cause of the radiation damage of BaF2 crystal in this paper.

New machining and polishing techniques have been developed for large scintillating crystal arrays such as the Barium Fluoride Electromagnetic Calorimeter for the GEM Detector at SSCL, the Crystal Clear Collaboration's cerium fluoride or lead tungstenate calorimeter at the proposed LHC at CERN, the PHENIX Detector at RHIC (barium fluoride), and the cesium iodide Calorimeter for the BaBar Detector at PEP-I B Factory at SLAC. The machining and polishing methods to be presented in this paper provide crystalline surfaces without sub-surface damage or deformation as verified by Rutherford Back-scattering (RBS) analysis. Surface roughness of about 10-20 angstroms and sub-micron mechanical tolerances have been demonstrated on large barium fluoride crystal samples. Mass production techniques have also been developed for machining the proper angled surfaces and polishing up to five 50 cm long crystals at one time. These techniques utilize kinematic mount technology developed at LLNL to allow precision machining and polishing of complex surfaces. We will present this technology along with detailed surface studies of barium fluoride and cerium fluoride crystals polished with this technique.

Barium fluoride (BaF{sub 2}) was discovered to be a fast inorganic scintillator in 1983. Considerable attention has been attracted in the fields of nuclear physics, nuclear medicine and high energy physics due to its high density, short radiation length, non-hygroscopic nature and high detection efficiency for {gamma}-rays. However, when BaF{sub 2} is exposed to a radiation environment, the fluorescence output will decrease, thus the study of the radiation damage mechanism of BaF{sub 2} is quite important. In this paper, the authors used the Discrete Variational X{sub {alpha}} (DV-X{sub {alpha}}) method to calculate the energy level of some rare earth doped BaF{sub 2} crystals and indicated that the Eu, Dy and Yb elements will change their valence from +3 to +2 under irradiation and thus change the optical properties of the crystals. The results show that this radiation effect model presented agree well with experiments.

Small barium fluoride crystals have been irradiated using cobalt-60 gamma rays under various illumination conditions to establish the effect of photo-bleaching of the radiation-induced color centers. This paper describes results of a few different experiments conducted at LLNL over the past few weeks.

The Papanicolaou (Pap) smear is the technique used to screen for abnormalities in cervical cells that may be related to cervical cancer and other problems. A number of research groups have reported results that indicate the infrared or NIR spectroscopy can be used to differentiate between samples of normal cervical cells and abnormal cells.In this paper we will describe studies performed on cervical cell samples with an infrared microscope and a motorized x-y stage. This configuration allowed us to “Map” the sample in 100 micron increments, where an infrared spectrum is acquired at each point. This integrated system also allowed chemometric algorithms developed with the Nicolet TQ Analyst software to be automatically applied to the spectral data. Samples of cervical cells were obtained from patients using the standard procedure. Part of the sample was used to prepare the Pap smear slide and the remainder was placed in a saline solution and centrifuged for several minutes. The cell suspension was then applied to a Barium Fluoride 5mm X 5mm window and dried.

Fluoride films (made from barium, calcium, strontium, and lead fluorides) tend to crystallize when they are sputtered. For an optical thickness more than 3-5 µm, their transparency in the visible region decreases because of losses to scattering. This paper discusses the optical characteristics of doped films of barium, calcium, strontium, and lead fluorides and shows that it is possible to obtain films that are simultaneously transparent in the visible and IR regions. Doped barium fluoride films were used as a basis for synthesizing, fabricating, and studying interference coatings that operate in the mid-IR and the visible regions. We give as an example coatings simultaneously used in laser systems with wavelengths of 10.6 and 0.63 µm. © 2004 Optical Society of America

In this paper we present a detailed analysis of the barium L3 and L1 EXAFS spectra of barium fluoride at 10 K and room temperature. Single and multiple scattering contributions have been calculated in the frame of the multiple scattering theory for a cluster including up to eleven shells using the Hedin-Lundqvist complex potential. The results show that the L1 and L3 EXAFS spectra.can be well reproduced only if X3 and X4 multiple scattering contributions are included.

This paper describes new compositions of self-lubricating coatings that contain chromium carbide. A bonded chromium carbide was used as the base stock because of the known excellent wear resistance and the chemical stability of chromium carbide. Additives were silver and barium fluoride/calcium fluoride eutectic. The coating constituents were treated as a ternary system consisting of: (1) the bonded carbide base material, (2) silver, and (3) the eutectic. A study to determine the optimum amounts of each constituent was performed. The various compositions were prepared by powder blending. The blended powders were then plasma sprayed onto superalloy substrates and diamond ground to the desired coating thickness. Friction and wear studies were performed at temperatures from 25 to 760 C in helium and hydrogen. A variety of counterface materials were evaluated with the objective of discovering a satisfactory metal/coating sliding combination for potential applications such as piston ring/cylinder liner couples for Stirling engines.

Alkalihalogenide (LiF, NaF, NaCl, NaBr, KCl, KBr, KJ) wurden im Hochvakuum auf (111)-Flachen von Calcium- und Bariumfluorid aufgedampft. Vor dem Bedampfen wurden die Tragerkristalle an der Luft gespalten. Die orientierte Kristallisation der isotypen Alkalihalogenide auf den beiden isotypen Substraten wird auf Grund zahlreicher elektronenmikroskopischer Aufnahmen beschrieben und diskutiert. Auser der (111)-Orientierung treten noch (100)-Orientierungen und bei den Fluoriden die (110)-Orientierung auf. Als Grundtendenz wird bei den Verwachsungsgesetzen der Einflus ubereinstimmender Symmetrie der simultanen Netzebenen deutlich. Bei Variation von Tragertemperatur und Ubersattigung kommt die Wirkung von Oberflachenstufen und Adsorptionsschichten auf die Epitaxie zum Ausdruck. Die Keimdichte zeigt einen Zusammenhang mit der Gitterenergie der Depositkristalle. Es wird der Versuch unternommen, einige Fragen vom Standpunkt der kinetischen Theorie der Epitaxie zu deuten. Alkali halides (LiF, NaF, NaCl, NaBr, KCl, KBr, KJ) have been deposited on (111)-faces of calcium- and barium fluoride in a high vacuum. Before deposition the substrate crystals have been cleaved in air. In this paper the oriented crystallization of the isotype alkali halides on the isotype substrates, studied by means of numerous electron micrographs, is described and discussed. Besides the (111)-orientation (100)-orientations occur and at the fluorides the (110)-orientation too. Principally the orientation relations are determined by the corresponding symmetry of the simultanous faces. The effect of surface steps and adsorption layers on epitaxy is observed in varying substrate temperature and supersaturation. Relations exist between the density of nuclei and the lattice energy of the deposite crystals. An attempt is made to interpret certain problems from the viewpoint of the kinetic theory of epitaxy.

This paper describes the results of a study of the effect of barium fluoride and zinc fluoride on enamels when added in the mill. These fluorides were used with high silica, high borax, high lead oxide, and high antimony oxide enamels. The effect of these fluorides upon opacity and the creation of such defects as crawling and crazing are shown by triaxial diagrams and photographs.

"Pure" Barium Fluoride has been found to scintillate to gamma rays and alpha and beta particles. Pulse height of 10% relative to NaI(Tl), emission decay of 0.63 microseconds, fluorescence emission maximum at 3250A have been measured for currently available crystals of BaF2. This paper describes the scintillation performance and pertinent physical properties of BaF2 in relation to some of the commercially available scintillators -- NaI (Tl), CsI(Na), CsI(Tl) and CaF2 (Eu). The low solubility, non-hygroscopic nature and a comparable absorption for gamma rays are particular advantages of BaF2 over the alkali iodide scintillators. Transmission to its fluorescence emission, shorter decay time and a better photelectric absorption cross-section favor BaF2 over CaF2 scintillators. However, the scintillation pulse height of BaF2 is presently lower than the other scintillators, but it is still sufficiently large enough to observe a resolvable Cs137 662 Kev photopeak. The mechanism responsible for scintillation in BaF2 is not well understood at present. A preliminary investigation to understand this mechanism was undertaken in the form of adding impurities of various valencies to BaF2 and also studying the behavior of scintillation with temperature. The data seems to indicate that hole-centers may be playing a primary role in the scintillation emission. An understanding of the mechanism and the improvement and development of BaF2 as a scintillator has been an integral part of the High Z Scintillator Research program maintained for some time by Harshaw.

The objective of this paper is to discuss the interaction of other fields with halide glasses and the impact of these interactions. The fields to be discussed are several fields of chemistry, sol-gel science and polymer fiber optics.

Subject of this paper is the interaction between laser radiation and surfaces of optically transparent ionic crystals at low‐power densities of the order of 106–107 W/cm2. By studying the wavelength and intensity dependencies of electron and ion‐emission yields, it is shown that surface states play a decisive role for photon absorption at surfaces of divalent ionic crystals. They resonantly enhance multiphoton processes which leads to a strong‐wavelength dependence of both photoemission and ion desorption. Cluster calculations confirm the existence of occupied surface states in the middle of the band gap and of unoccupied states in its upper half as well as above the ionization limit. The dependence on laser intensity reveals both two‐ and five‐photon processes for photoemission, and ten‐photon processes for the desorption of positive ions. The latter is interpreted as the creation of two holes, each by five‐photon absorption, with subsequent Coulomb repulsion of a positive ion.