Search

Spectra of weakly-bound hydrogen-xenon complexes are studied in equilibrium gas mixtures at relatively high spectral resolution (0.04 [cm.sup.-1]) using a long-path (112 m), low-temperature (140 K) absorption cell and a Fourier transform infrared spectrometer. The data cover the regions of the [H.sub.2] and [D.sub.2] fundamental stretching vibrations in the mid-infrared (λ ~ 2.4,3.3 µm), and are greatly improved compared to the only previous observation. The results serve as a stringent experimental benchmark for testing theoretical hydrogen-xenon intermolecular potential energy models, as well as forming the basis for deriving an improved semi-empirical potential. PACS Nos.: 33.20.Ea, 31.50, 33.15, 36.40.c. L'utilisation d'un spectrometre infrarouge a transformee de Fourier, avec un long bras (112 m) et une cellule d'absorption de basse temperature (140 K), nous a permis d'etudier en haute resolution le spectre du complexe faiblement lie d'hydrogene-xenon. Les donnees couvrent la region des vibrations d'elongation [H.sub.2] et [D.sub.2] du fondamental dans l'infrarouge moyen et sont d'une qualite nettement superieure au seul autre ensemble de donnees existant. Les resultats serviront de critere severe pour tester les modeles d'energie potentielle theoriques intermoleculaires hydrogene-xenon, aussi bien que de base pour developper un potentiel semi-empirique ameliore., 1. Introduction Weakly-bound complexes containing a hydrogen molecule and a rare gas (Rg) atom were some of the first van der Waals molecules to be studied spectroscopically at high (i.e., [...]

Suspect 'ecstasy' tablets have been analyzed using attenuated total internal reflection Fourier-transform infrared (ATR-FT-IR) spectroscopic imaging to confirm the presence of several controlled substances that were first identified using liquid [...]

Based on the Fourier transform infrared spectrometer, a system for measuring the loss spectrum of hollow fiber is established. Loss spectra can be measured for hollow fibers with length ranging from several centimeters to 3 m. Two kinds of light source coupler are designed and fabricated for achieving stable coupling and a repeatable spectrum. One is a short waveguide, and the other is a tapered tube. Both are inner-coated with a silver layer and they are of the same inner diameter at the output end as the measured hollow fiber. Characteristics of the measuring system are discussed theoretically and experimentally when using the two couplers. Several kinds of hollow fibers are measured, and the properties of the loss spectra are discussed. The measured loss value is shown to be dependent on the output divergence angle of the coupler. The tapered coupler has a larger output divergence and causes higher measured loss than that of the waveguide coupler. [c] 2010 Optical Society of America OCIS codes: 230.7370, 310.6860, 120.7000, 060.2270, 120.6200.

We apply photon-trap spectroscopy, a generalized scheme of cavity ringdown spectroscopy, to infrared spectroscopy of molecular adsorbates on a solid substrate. The storage lifetime of light in a high-finesse Fabry--Perot cavity provides a high absorbance sensitivity for the substrate sample, which is placed exactly normal to the light beam in the cavity to minimize optical losses. Infrared spectra of the C--H stretching vibration of alkylsiloxane monolayer films on a silicon substrate are measured in three ways, namely by employing pulsed and continuous-wave lasers as well as by conventional Fourier transform infrared spectroscopy. The magnitude of optical absorption is shown to vary by the character of the interacting light used in the measurement, i.e., a standing wave versus a propagating wave. OCIS codes: 120.6200, 300.1030, 300.6250.

The composite infrared spectrometer (CIRS) instrument on board the Cassini Saturn orbiter employs two 1 x 10 HgCdTe detector arrays for mid-infrared remote sensing of Titan's and Saturn's atmospheres. In this paper we show that the real detector spatial response functions, as measured in ground testing before launch, differ significantly from idealized 'boxcar' responses. We further show that neglecting this true spatial response function when modeling CIRS spectra can have a significant effect on interpretation of the data, especially in limb-sounding mode, which is frequently used for Titan science. This result has implications not just for CIRS data analysis but for other similar instrumental applications. OCIS codes: 010.0280, 010.1280, 040.3060, 040.5160, 120.0280, 300.6340.

A method based on Fourier transform infrared (FTIR) double-pass transmittance spectroscopy was developed for determining functional group loading in size-segregated ambient aerosol deposits. The impactor employed for sample collection utilized rotating stages, which produced uniform particulate matter (PM) deposits on standard Al foil substrates. Each sample was analyzed without extraction using an FTIR spectrometer equipped with a reflectometer accessory. The use of the reflectometer obviated the need for infrared window materials as substrates. [([NH.sub.4]).sub.2]S[O.sub.4] aerosol generated under laboratory conditions were used to calibrate deposit mass to the band strength of the relatively isolated [v.sub.4] bending mode of S[O.sup.2-.sub.4] centered near 620 [cm.sup.-1]. Atmospheric PM was sampled during the summer of 2004 in Huntsville, Ala. Sulfate concentrations determined in this initial study correlated well with measurements made by collocated EPA air samplers. OCIS codes: 300.6300, 010.1280, 120.6200.

We report a method that uses near-infrared spectroscopy and multivariate analysis to measure the temperature of turbid aqueous solutions. The measurement principle is based on the fact that the peak wavelength of the water absorption band, with its center near 1440 nm shifts with changes in temperature. This principle was used to measure the temperatures of 1 mm thick samples of aqueous solutions containing Intralipid (2%), which are often used as optical phantoms for biological tissues due to similar scattering characteristics. Temperatures of pure water and aqueous solutions containing glucose (100 mg/ml and 200mg/ml) were also measured for comparison. For the turbid Intralipid solutions, the absorbance spectrum varied irregularly with time due to the change in scattering characteristics. However, by making use of the difference between the absorbance at 1412 nm and the temperature-independent absorbance at 1440nm, we obtained SEPs (standard error of prediction) of 0.3 [degrees]C and 0.2 [degrees]C by univariate linear regression and partial least squares regression, respectively. These accuracies were almost the same as those for the transparent samples (pure water and glucose solution). OCIS codes: 120.6780, 300.6340.

We demonstrate methane sensing based on Fourier transform infrared spectroscopy using a hollow-core photonic bandgap fiber guiding in the mid-infrared and idler pulses from a femtosecond optical parametric oscillator. Transmission measurements are presented for several fibers, and sensing is demonstrated using a fiber whose bandgap overlaps the methane fundamental absorption lines. The gas filling process of the air core is described, and qualitative methane concentrations measurements to 1000ppm (parts in [10.sup.6]) are reported. Operation down to 50 ppm based on our current experiment is predicted. OCIS codes: 060.2370, 060.2390, 060.5295, 300.1030, 300.6340.

Transmission measurements of 14 fabrics are presented in the millimeter-wave and submillimeter-wave electromagnetic regions from 130 GHz to 1.2 THz. Three independent sources and experimental setups were used to obtain accurate results over a wide spectral range. Reflectivity, a useful parameter for imaging applications, was also measured for a subset of samples in the submillimeter-wave regime along with polarization sensitivity of the transmitted beam and transmission through doubled layers. All of the measurements were performed in free space. Details of these experimental setups along with their respective challenges are presented. OCIS codes: 260.3090, 300.6270.

We have determined the glucose concentration of whole blood from mid-infrared spectra without sample preparation or use of chemical reagents. We selected 1119-1022 [cm.sup.-1] as the optimal wavelength range for our measurement by making a first-loading vector analysis based on partial least-squares regression. We examined the influence of hemoglobin on samples by using different calibration and prediction sets. The accuracy of glucose prediction depended on the hemoglobin level in the calibration model; the sample set should represent the entire range of hemoglobin concentration. We obtained an accuracy of 5.9% in glucose prediction, and this value is well within a clinically acceptable range. OCIS codes: 170.1470, 170.1580, 170.4580, 170.6510.

An experimental system in which correlated photons for radiometric measurements were used has been set up at the National Institute of Standards and Technology. We use visible-IR pairs of correlated photons produced by means of optical parametric downconversion te measure the radiance of a high-temperature IR source at 3.415 and 4.772 [[micro]meter] in an intrinsically absolute manner (i.e., without requiring any externally calibrated radiometric standard). To our knowledge, this is the only radiometric method with which one measures radiance directly, instead of using radiant power and aperture geometry measurements to deduce radiance indirectly. This technique has an additional unusual characteristic: It allows absolute radiometric measurements of IR radiation to be made with high-quality visible detectors. We compare measurements made with this technique with radiance measurements made with conventional means tied to existing radiometric standards. These comparisons show an average agreement to within -3% between the two methods. The results demonstrate an accuracy consistent with the estimated uncertainty of the current measurements. This is the first time to our knowledge that this method has been used to provide absolute radiance measurements of a source that has been calibrated conventionally, revealing unexpected systematic effects and allowing estimates of the ultimate accuracy of this method. In addition, these measurements are further into the IR than any previous measurements of this process and have produced the highest thermally stimulated downconversion signal yet seen.

We report the strengths and locations of the absorption lines of C[H.sub.3]D, 13C[H.sub.4], and 12C[H.sub.4] in the vicinity of the helium-neon laser line at 2999.24 [cm.sup.-1]. In this region we find intrinsically strong lines of the rare species overlapping, but not precisely coincident with, intrinsically weak lines of the major species. In methane of normal isotopic composition, the lines of all three species have comparable strengths. We show how absorption measurements of the He-Ne laser, with Zeeman splitting, can be used to determine variations of the concentrations of the rare species from standard concentrations at a calculated precision of 0.5%. Key words: Methane, isotopic species, laser, helium-neon, Zeeman effect.

The application of Kramers-Kronig analysis for reflection spectra from a single interface with perpendicular (s) polarization has been studied theoretically with regard to a phase correction term. The errors in phase shift and complex refractive index obtained by the use of Kramers-Kronig analysis have been examined for such techniques as external, internal, and total internal reflection spectroscopies by the use of spectral simulation and the complex refractive index based on dispersion theory. The advantages and disadvantages of the various measurement techniques used to obtain the complex refractive index of a sample material have been compared. It is concluded that the external reflection technique can be used until the sample thickness becomes too thin to provide the edge shape necessary to avoid the detection of reflection from the back surface. The total internal reflection technique should be used only for a thin-film sample because knowledge of the refractive index at some frequency is required and because this technique may yield larger errors than the other techniques in the complex refractive index obtained by the use of Kramers-Kronig analysis.

The characterization of the silicon surface structures and oxidation processes at room temperature by multiple internal reflection (MIR) infrared (IR) spectroscopy is discussed. This involves the utilization of a Fourier transform infrared spectrophotometer, a germanium prism as a MIR element and a MIR attachment. The utility of MIR-IR spectroscopy for the analysis of standard silicon wafers was demonstrated.

A new method of infrared spectroscopy was used to investigate the electron mobility and carrier concentration in GaAs lightly doped with Si grown by molecular beam epitaxy on Si(100) substrates. The new approach was nondestructive and combined a conventional reflectance measurement with a transmittance measurement in the very far-infrared range. As compared with data obtained from Hall measureements, the results using the infrared method was simpler, easier to perform and provided accurate data despite complications posed by the low doping and dimensions of the films.

We describe a portable diode-laser-based sensor for [NH.sub.3] detection using vibrational overtone absorption spectroscopy at 1.53 [micro]m. Use of fiber-coupled optical elements makes such a trace gas sensor rugged and easy to align. On-line data acquisition and processing requiring [is less than] 30 s can be performed with a laptop PC running LabVIEW software. The gas sensor was used primarily for [NH.sub.3] concentration measurements with a sensitivity of 0.7 parts per million (signal-to-noise ratio of 3) over a two-week period in a bioreactor being developed at the NASA Johnson Space Center for water treatment technologies to support long-duration space missions. The feasibility of simultaneous, real-time measurements of [NH.sub.3] and [CO.sub.2] concentrations is also reported. OCIS codes: 300.6360, 140.3490, 280.3420.