Connectors, splices, and couplers for infrared transmitting optical fibers

Connectors, splices, and couplers are widely used in silica optical fiber systems. Until now they have not been developed for mid-infrared fibers, in spite of the recognized need for such elements in many applications such as spectroscopy, radiometry, and heterodyne detection. We describe the construction and the optical and mechanical properties of such optical components for infrared transmitting silver halide optical fibers.     

Relativistic effects, infrared intensities, diffusion and lithiation in InSb

We consider In₄Sb₄H₁₈ cluster with zinc-blend structure of InSb. The cohesive energy and band gap of InSb were calculated by Unrestricted Hartree–Fock (UHF) and Density Functional Theory (DFT) method and it was shown that underestimated values of band gap can be decreased by considering the relativistic effects and in some cases InSb crystal even to be a semimetal. By calculating time-dependent DFT (TDDFT), the first three singlet and triplet excited energies were calculated and it was shown the 0.23 eV (band gap of InSb at 77 K) is placed between them. The infrared intensities were calculated and it is shown that the 367 cm⁻¹ (294 cm⁻¹ experimentally) mode can be attributed to the LO(Γ) in InSb. Finally it was shown that the Cadmium (Cd) diffuses substantially as Cd_In and changes the first three singlet and triplet excited energies, but Lithium (Li) is placed in empty spaces of InSb crystal in the lithiation of InSb.     

Electrical,thermal and infrared studies of cadmium metavanadate

Cadmium(II) metavanadate has crystal structure related to brannerite (ThTi₂O₆) structure. The high temperatureβ-CdV₂O₆ phase isn-type semiconductor between 185 and 750°C. The electrical conduction in theβ-CdV₂O₆ occurs due to deviation from oxygen stoichiometric composition of the lattice. The seebeck coefficient (α) of the sample is negative and constant in the entire range of investigation. The mechanism of transport in cadmium metavanadate lattice is via thermally activated hopping of localized electrons on vanadium (V⁵⁺) sites of the lattice. The DTA result indicated that CdV₂O₆ undergoes phase transition at 185°C and not at 670°C as reported earlier. There is no DTA evidence to show the possibility ofβ →α phase reverse transition. The XRD powder patterns of the two modifications are nearly similar indicating brannerite related structures. The infrared absorption band of vanadium-oxygen stretching vibration modes of distorted VO₆ octahedra ofβ-CdV₂O₆ is exhibited at 855 cm⁻¹.     

Optical properties of the metals Al, Co, Cu, Au, Fe, Pb, Ni, Pd, Pt, Ag, Ti, and W in the infrared and far infrared

Infrared optical constants collected from the literature are tabulated. The data for the noble metals and Al, Pb, and W can be reasonably fit using the Drude model. It is shown that -epsilon1(omega) = epsilon2(omega) approximately omega(2)(p)/(2omega(2)(tau)) at the damping frequency omega = omega(tau). Also -epsilon1(omega(tau)) approximately - (1/2) epsilon1(0), where the plasma frequency is omega(p).     

Comparison of temperature resolution of single-band, dual-band, and multiband infrared systems

A new measure of temperature resolution of IR systems called noise-generated error (NGE) was recently proposed. The NGE does not have limitations of the classical noise-equivalent temperature difference and can be used to describe the resolution of single-band, dual-band, and multiband IR measurement systems. The results of theoretical and experimental testing of the temperature resolution NGE of a developed model of single-band, dual-band, and multiband pyrometers are presented.     

Helical polyurethane-imide@attapulgite composite: Preparation, characterization and infrared emissivity study

Helical polyurethane-imide@attapulgite (HPUI@ATT) composite has been successfully prepared based on the surface modification of attapulgite (ATT). The results indicate that helical polyurethane-imide has been grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. The infrared emissivity of HPUI@ATT was also investigated, and the result indicates that the infrared emissivity value of HPUI@ATT composite is reduced to 0.628 at the wavelength of 8-14 μm, while the bare ATT possesses a value of 0.934. This effect could be attributed to the interfacial interactions between organics (helical polyurethane-imide) and inorganics (ATT). This paper will provide the foundation for many potential applications such as infrared low-emissive materials and other fields in the future.     

X-ray,electrical conductivity,and infrared studies of oxide spinels containing cobalt,titanium and manganese

X-ray, electrical conductivity and infrared studies of the system Co_2–x Ti_1–x Mn_2x O₄ were carried out with a view to investigate the cation distribution. Compounds 0 x 0.6 showed cubic symmetry, compounds 0.8 x 1 are tetragonal. X-ray intensity calculation indicated the presence Of Co²⁺ and Mn³⁺ at both octahedral and tetrahedral sites. A plot of activation energy against composition shows a break where crystal symmetry changes. The electrical conductivity-temperature behaviour obeys the Raschhinrichsen law. The mobility of holes calculated from infrared and conductivity data is of the order Of 10^–9 cm² V^–1 sec^–1. X-ray intensity calculations and conductivity measurements suggest the ionic configuration of the system to be Co _1–x ²⁺ Mn _x ³⁺ [Co _2–2x ²⁺ Mn _x ³⁺ Ti _x ⁴⁺ ]O ₄ ^2– .     

Variable path length transmittance cell for ultraviolet, visible, and infrared spectroscopy and spectroelectrochemistry

The design and characteristics of a transmittance cell for ultraviolet, visible, and infrared spectroscopy and spectroelectrochemistry are described. Through modification of a previously reported design, this cell employs threaded glass connectors as insertion ports for either quartz- or silicon-windowed tubes, thus permitting essentially continuous variation of the optical path length from ～0.050 to 200 mm. Though the initial fabrication requires skillful glassblowing, once constructed, the cell's simple design allows for rapid and reproducible disassembly/reassembly between experiments. The utility of the cell for a diversity of fluid samples is demonstrated through applications to water, aqueous ferricyanide, ferrocene in methylene chloride, and acetone vapor.     

Modeling, fabrication, and characterization of tungsten silicide wire-grid polarizer in infrared region

We designed and fabricated a tungsten silicide wire-grid polarizer. To examine its polarization characteristics, the transmission spectra of the polarizer were simulated using the effective medium theory. The polarizer was fabricated based on the simulation results. The transverse magnetic (TM) polarization transmittance of the fabricated polarizer was greater than 50% over the 5 mum wavelength, and the ratio of TM and transverse electric transmittance was greater than 100 (20 dB) in the infrared range. This fabricated polarizer has higher durability and better compatibility with microfabrication processes than conventional infrared polarizers.     

Characterization of atmospheric aerosols from infrared measurements: simulations, testing, and applications

An inversion method for the characterization of atmospheric condensed phases from infrared (IR) spectra is described. The method is tested with both synthetic IR spectra and the spectra of particles that flow in a cryogenic flow tube. The method is applied to the IR spectra recorded by the Atmospheric Trace Molecule Spectroscopy instrument carried by the Space Shuttle during three missions in 1992, 1993, and 1994. The volume density and particle size distribution for sulfate aerosol are obtained as a function of altitude. The density and size distribution of ice particles in several cirrus clouds are also retrieved. The probable radius of the ice particles in the high-altitude (10-15-km) cirrus clouds is found to be approximately 6-7 microm.     

Noise, clutter, and determinism in infrared spectral signatures under varying meteorological conditions

Infrared remote detection of chemical and biological agents in a complex environment depends on the ability to recognize threat signatures and differentiate them from the signatures of innocuous materials. In this paper, we addressed the methods of producing the constraint spectra needed to ensure reliable operation in a meteorologically changing environment. We collected arrays of background spectra of ground, woods, and low-angle sky on an irregular basis over a period of a year. Based on the hypothesis that the concentration fluctuations of species in the sensor's field of view can be exploited to form signatures, the standard deviations of the array (the result is characteristic of all fluctuations) and the difference array (the result is characteristic of sensor fluctuations) were computed. Subtracting these two spectra and filtering the result produced a spectrum, which is a measure of the IR fluctuations in the scene. The resulting set of scene spectra were processed into aberrant noise, and deterministic groups by numerical filtering and statistical methods.     

A microcavity-controlled, current-driven, on-chip nanotube emitter at infrared wavelengths

Recent studies of the optical properties of semiconducting single-walled carbon nanotubes suggest that these truly nanometre-scale systems have a promising future in nanophotonics, in addition to their well-known potential in electronics. Semiconducting single-walled nanotubes have a direct, diameter-dependent bandgap and can be excited readily by current injection, which makes them attractive as nano-emitters. The electroluminescence is spectrally broad, spatially non-directional, and the radiative yield is low. Here we report the monolithic integration of a single, electrically excited, semiconducting nanotube transistor with a planar lambda/2 microcavity, thus taking an important first step in the development of nanotube-based nanophotonic devices. The spectral full-width at half-maximum of the emission is reduced from approximately 300 to approximately 40 nm at a cavity resonance of 1.75 microm, and the emission becomes highly directional. The maximum enhancement of the radiative rate is estimated to be 4. We also show that both the optically and electrically excited luminescence of single-walled nanotubes involve the same E11 excitonic transition.     

Near infrared and mid infrared investigations of adsorbed phenol on HDTMAB organoclays

X-ray diffraction patterns (XRD), infrared Spectroscopy (IR) and near infrared spectroscopy (NIR) have been used to measure the adsorption of phenol on untreated montmorillonite and on hexadecyltrimethylammonium bromide (HDTMAB) modified montmorillonite. The mid infrared spectra indicate that both the surfactant molecule and phenol enter the interlayer of organoclays, replacing the interlayer cations. The higher concentration surfactant leads to a decrease in wavenumber of the bands of organoclays and to increase in intensity. The near infrared spectra (9000–4000 cm^?1) show a prominent band 8260 cm^?1, assigned to the combination result of the CH stretching vibrations of high concentration surfactant and absorbed phenol. The main band observed at 7090 cm^?1 is assigned to the first fundamental overtone of the OH stretching vibrations at 3415 cm^?1 for organoclay. The organoclays are characterised by prominent bands situated between 5900 and 5700 cm^?1. Both the higher concentration of organic molecules and adsorbed phenol causing the near infrared spectra of organic clays to be more complex for spectra in the region from 4700 to 5500 cm^?1. The main band of 4535 cm^?1 for montmorillonite shifts towards the lower wavenumber sites for higher concentration organoclay. The intensity of near infrared spectra generally rises with the value of surfactant concentration increasing, showing certain regularity. It is concluded that phenol is adsorbed to significantly greater amounts on the higher concentration organoclays.     

Lensed-taper launching coupler for small-bore, infrared hollow fibers

A new type of launching coupler for small-bore, hollow fibers, consisting of a lens and a tapered hollow waveguide, is proposed to increase the alignment tolerance between an input laser beam and small bore fibers. First, we designed the structural dimensions of the coupler by using a ray-tracing method. Then, a series of experiments employing tapered hollow waveguides made of Pyrex glass was performed to investigate the effectiveness of the new coupler. It is shown that the coupler has a high efficiency with attenuation of around 0.5 dB, especially when the inside of the taper section is coated with a polymer and silver film. In addition, we also show that the coupler has great tolerance for the transverse displacement of a waveguide axis, which gives a 0.1-dB loss increase for a 300-mum displacement.     

HN22 sheet polarizer, an inexpensive infrared retarder

The popular sheet polarizer, Polaroid HN22, has been measured to be a nearly half-wave retarder in the 3.6-5.4-mum spectral band with a transmittance of approximately 20%. Tuning of the retardance value between 60 degrees and 260 degrees has been demonstrated by tilting of the HN22 sheet with respect to the incident beam. The material's availability, relatively large aperture, large field of view, and low cost make it an excellent candidate for use as an infrared retarder for systems operating in this wave band. Thus HN22 may be employed as an inexpensive half-wave linear retarder and used for rotating the plane of polarization as well as for conversion between circular polarization states.     

Detection,identification, and estimation of biological aerosols and vapors with a Fourier-transform infrared spectrometer

Two experiments were conducted with a Fourier-transform infrared (FTIR) spectrometer. The purpose of the first experiment was to detect and identify Bacillus subtilis subsp. niger (BG) bioaerosol spores and kaolin dust in an open-air release for which the thermal contrast between the aerosol temperature and background brightness temperature is small. The second experiment estimated the concentration of a small amount of triethyl phosphate (TEP) vapor in a closed chamber in which an external blackbody radiation source was used and where the thermal contrast was large. The deduced BG (TEP) extinction spectrum (identification) showed an excellent match to the library BG (TEP) extinction spectrum. Analysis of the time sequence of the measurements coincided well with the presence (detection) of the BG during the measurements, and the estimated concentration of time-dependent TEP vapor was excellent. The data were analyzed with hyperspectral detection, identification, and estimation algorithms. The algorithms were based on radiative transfer theory and statistical signal-processing methods. A subspace orthogonal projection operator was used to statistically subtract the large thermal background contribution to the measurements, and a robust maximum-likelihood solution was used to deduce the target (aerosol or vapor cloud) spectrum and estimate its mass-column concentration. A Gaussian-mixture probability model for the deduced mass-column concentration was computed with an expectation-maximization algorithm to produce the detection threshold, the probability of detection, and the probability of false alarm. The results of this study are encouraging, as they suggest for the first time to the authors' knowledge the feasibility of detecting biological aerosols with passive FTIR sensors.     

Electrical,thermal and infrared studies of cerium(III) orthovanadate

Cerium(III) orthovanadate with a small deviation from stoichiometric composition is ap-type semiconductor between 30 and 800°C. The electrical conduction in cerium(III) orthovanadate is due to thermally activated hopping of holes on equivalent Ce³⁺-Ce⁴⁺ lattice sites. The DTA result of CeVO₄ indicated a possible phase transition at about 70°C. The IR spectrum of the sample showed bands at 865 and 810 cm⁻¹, typical of VO₄ group of orthovanadates.