High-resolution Infrared Research Articles

Multiple integration method for a high signal-to-noise ratio readout integrated circuit

A multiple integration method is reported that greatly improves the signal-to-noise ratio (SNR) for applications with a high-resolution infrared (IR) focal plane array. The signal from each pixel is repeatedly sampled into an integration capacitor and then output and summed into an outside memory that continues for n read cycles during each period of a frame. This method increases the effective capacity of the charge integration and improves sensitivity. Because a low-noise function block and high-speed operation of the readout circuit is required, a new concept is proposed that enables the readout circuit to perform digitization by a voltage skimming method. The readout circuit was fabricated using a 0.6-/spl mu/m CMOS process for a 64/spl times/64 midwavelength IR HgCdTe detector array. The readout circuit effectively increases the charge storage capacity to 2.4/spl times/10/sup 8/ electrons and then provides a greatly improved SNR by a factor of approximately 3.

Sensitivity Analysis of Cirrus Cloud Properties from High-Resolution Infrared Spectra. Part I: Methodology and Synthetic Cirrus

AbstractA set of simulated high-resolution infrared (IR) emission spectra of synthetic cirrus clouds is used to perform a sensitivity analysis of top-of-atmosphere (TOA) radiance to cloud parameters. Principal component analysis (PCA) is applied to assess the variability of radiance across the spectrum with respect to microphysical and bulk cloud quantities. These quantities include particle shape, effective radius (reff), ice water path (IWP), cloud height Zcld and thickness ΔZcld, and vertical profiles of temperature T(z) and water vapor mixing ratio w(z). It is shown that IWP variations in simulated cloud cover dominate TOA radiance variability. Cloud height and thickness, as well as T(z) variations, also contribute to considerable TOA radiance variability.The empirical orthogonal functions (EOFs) of radiance variability show both similarities and differences in spectral shape and magnitude of variability when one physical quantity or another is being modified. In certain cases, it is possible to identify the EOF that represents variability with respect to one or more physical quantities. In other instances, similar EOFs result from different sets of physical quantities, emphasizing the need for multiple, independent data sources to retrieve cloud parameters. When analyzing a set of simulated spectra that include joint variations of IWP, reff, and w(z) across a realistic range of values, the first two EOFs capture approximately 92%–97% and 2%–6% of the total variance, respectively; they reflect the combined effect of IWP and reff. The third EOF accounts for only 1%–2% of the variance and resembles the EOF from analysis of spectra where only w(z) changes. Sensitivity with respect to particle size increases significantly for reff several tens of microns or less. For small-particle reff, the sensitivity with respect to the joint variation of IWP, reff, and w(z) is well approximated by the sum of the sensitivities with respect to variations in each of three quantities separately.

Rotational analysis of bands in the high-resolution infrared spectra of the three species of butadiene-1,4- d2; refinement of the assignments of the vibrational fundamentals

Samples of trans, trans and cis, cis forms of butadiene-1,4- d 2 have been synthesized and found to contain useful amounts of the cis, trans species as a contaminant. Assignments of fundamental frequencies for the three isotopomers of butadiene-1,4- d 2 have been extended and improved from investigations of their Raman spectra as well as their infrared (IR) spectra. High-resolution IR spectra have been recorded for the three isotopomers, and a rotational analysis has been completed for strong bands of each species. Ground state and some upper state rotational constants have been fit. Corresponding ground state moments of inertia compare favorably with equilibrium moments of inertia obtained from B3LYP/6-311++G** theory. Two 13C isotopomers are being prepared, and an improved structural analysis of butadiene will soon be available to assess how π-electron delocalization affects its structure.

Analysis of the rotational structure in bands in the high-resolution infrared spectra of butadiene and butadiene-2,3-d2: refinement in assignments of fundamentals*1

Rotational constants for butadiene and butadiene-2,3- d 2 are derived from the analysis of the rotational structure of bands in the high-resolution infrared (IR) spectra. Corresponding moments of inertia computed from three quantum chemical calculations agree acceptably with the experimental values. Evidence is growing that the CC bond lengthens some and the C–C bond shortens some in support of partial π-electron delocalization in butadiene. Refinements are made in the assignment of vibrational fundamentals of butadiene and butadiene-2,3- d 2 from new observations of IR and Raman spectra of these species.

Analysis of the rotational structure in bands in the high-resolution infrared spectra of butadiene and butadiene-2,3- d2: refinement in assignments of fundamentals

Rotational constants for butadiene and butadiene-2,3- d 2 are derived from the analysis of the rotational structure of bands in the high-resolution infrared (IR) spectra. Corresponding moments of inertia computed from three quantum chemical calculations agree acceptably with the experimental values. Evidence is growing that the CC bond lengthens some and the C–C bond shortens some in support of partial π-electron delocalization in butadiene. Refinements are made in the assignment of vibrational fundamentals of butadiene and butadiene-2,3- d 2 from new observations of IR and Raman spectra of these species.

Inference of ice cloud properties from high spectral resolution infrared observations

The theoretical basis is explored for inferring the microphysical properties of ice clouds from high spectral resolution infrared (IR) observations. Extensive radiative transfer simulations are carried out to address relevant issues. The single-scattering properties of individual ice crystals are computed from state-of-the-art light scattering computational methods and are subsequently averaged for 30 in situ particle size distributions and for four additional analytical Gamma size distributions. The nonsphericity of ice crystals is shown to have a significant impact on the radiative signatures in the IR spectrum. Furthermore, the errors associated with the use of the Henyey-Greenstein phase function can be larger than 1 K in terms of brightness temperature for large particle effective sizes (/spl sim/80 /spl mu/m) at wavenumbers where the scattering of the IR radiation by ice crystals is not negligible. The simulations undertaken in this paper show that the slope of the IR brightness temperature spectrum between 790-960 cm/sup -1/ is sensitive to the effective particle size. Furthermore, a strong sensitivity of the IR brightness temperature to cloud optical thickness is noted within the 1050-1250-cm/sup -1/ region. Based on these spectral features, a technique is presented for the simultaneous retrieval of the visible optical thickness and effective particle size from high spectral resolution IR data for ice clouds. An error analysis shows that the uncertainties of the retrieved optical thickness and effective particle size have a small range of variation. The error for retrieving particle size in conjunction with an uncertainty of 5 K in cloud temperature, or a surface temperature uncertainty of 2.5 K, is less than 15%. The corresponding errors in the uncertainty of optical thickness are within 5% to 20%, depending on the value of cloud optical thickness. The applicability of the present retrieval technique is demonstrated using airborne high-resolution IR measurements obtained during two field campaigns.

The thermal structure of a wind-driven Reynolds ridge

In this study, we investigate the nature of a Reynolds ridge formed by wind shear. We have simultaneously imaged the water surface, with a deposit of a monolayer of the surfactant, oleyl alcohol, subject to different wind shears, by using a high-resolution infrared (IR) detector and a high-speed (HS) digital camera. The results reveal that the regions around the wind-driven Reynolds ridge, which have subtle manifestations in visual imagery, possess surprisingly complex hydrodynamical and thermal structures when observed in the infrared. The IR measurements reveal a warm, clean region upstream of the ridge, which is composed of the so called fishscale structures observed in earlier investigations. The region downstream of the ridge is composed of colder fluid which forms two counter-rotating cells. A region of intermediate temperature, which we call the mixing (wake) region, forms immediately downstream of the ridge near the channel centerline. By measuring the velocity of the advected fishscales, we have determined a surface drift speed of about 2% of the wind speed. The spanwise length-scale of the structures has also been used to estimate the wind shear. In addition, a comparison of IR and visual imagery shows that the thermal field is a very sensitive indicator of the exact position of the ridge itself.

Polymerization and light-induced heat of dental composites cured with LED and halogen technology

Most commercial light curing units (LCUs) for dental applications use conventional halogen bulbs. Commercial LCUs using light emitting diodes (LEDs) have recently become established on the market, even though some aspects of their performance have not been fully investigated. Temperature rise of dental composites during the light-induced polymerization is considered to be a potential hazard for the pulp of the tooth. This study, therefore, investigated the temperature rise in three different composites (Z100, Durafill, Solitaire2) in two shades (A2, A4) polymerized for 40 s with two LED LCUs (Freelight, custom-made LED LCU prototype) and two halogen LCUs (Trilight, Translux). The Trilight was used in the standard and soft-start mode. The temperature rise within the composites were recorded for 60 s with a thermocouple and also observed with a high-resolution infrared (HRIR) camera. The factors LCU ( p<0.0001), composite ( p<0.0001) and shade ( p=0.0014) had statistically significant influences on the temperature rise. All composites cured with the halogen LCUs reached at a depth of 2 mm, a statistically significant higher temperature ( p<0.0001) than those cured with the LED LCUs. Only one composite showed a statistically significant lower temperature rise for the halogen LCUs at the 95% confidence level, when the soft-start mode was used instead of the standard mode. In general, the composites with the lighter shade (A2) reached higher temperatures than the darker shade (A4), if the LED LCUs were used. When the halogen LCUs were used, the situation was reversed, the composites with the darker shade (A4) reaching higher temperatures than the lighter shade (A2). This study showed that a HRIR camera represents a powerful tool for the observation of temperature propagation on small samples. This study also showed that LED LCUs represent a viable alternative to halogen LCUs for the light polymerization of dental composites because of a generally lower temperature increase within the composite.

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Kettle Creek and Cooks Run Basins, Pennsylvania, USA

High-resolution airborne thermal infrared (TIR) imagery data were collected over 90.6 km2 (35 mi2) of remote and rugged terrain in the Kettle Creek and Cooks Run Basins, tributaries of the West Branch of the Susquehanna River in north-central Pennsylvania. The purpose of this investigation was to evaluate the effectiveness of TIR for identifying sources of acid mine drainage (AMD) associated with abandoned coal mines. Coal mining from the late 1800s resulted in many AMD sources from abandoned mines in the area. However, very little detailed mine information was available, particularly on the source locations of AMD sites. Potential AMD sources were extracted from airborne TIR data employing custom image processing algorithms and GIS data analysis. Based on field reconnaissance of 103 TIR anomalies, 53 sites (51%) were classified as AMD. The AMD sources had low pH (<4) and elevated concentrations of iron and aluminum. Of the 53 sites, approximately 26 sites could be correlated with sites previously documented as AMD. The other 27 mine discharges identified in the TIR data were previously undocumented. This paper presents a summary of the procedures used to process the TIR data and extract potential mine drainage sites, methods used for field reconnaissance and verification of TIR data, and a brief summary of water-quality data.

High-Resolution Study of Light and Heat Patterns in Infrared Emitting Devices

ABSTRACTWe report on light and heat distributions in the active area of infrared lasers and light-emitting diodes operating at 300 K in the 0, 8–4,7 μm spectral range. To separate light and heat produced by these devices, we developed a high-resolution multi-spectral infrared (&lt;1 m, 3–5 m and 8–12 m ranges) “vision” facility capable of providing &lt;20 m spatial resolution and 10 s temporal resolution. We show how current crowding and Joule heating combined drastically decrease integral power emitted by light-emitting diodes and provoke remarkable non-uniformity in light and heat maps. As concerning stripe lasers, we comment on heat spreading and heat bottlenecks inside the laser dome and quality of heat sink.

Functional infrared imaging of the breast.

In order to re-assess the potential contribution of infrared (IR) imaging as a first-line component of a multi-imaging strategy using currently available technology, we first review the history of its introduction and clinical application, including the results of the Breast Cancer Detection Demonstration Projects (BCDDP). We then discuss experiments with a new high-resolution, computerized IR station and software program acquired by the Ville Marie Breast Center to assess IR imaging's ability to complement clinical examination and mammography in the early detection of breast cancer. Our goal is to show that high-resolution IR imaging provides additional safe, practical, and objective information when produced and interpreted by sufficiently trained breast physicians.

NC 3NC: a combined millimetre-wave spectroscopic and ab initio investigation

The millimetre-wave spectrum of 2-isocyano-3-propynenitrile, NC 3NC, was observed in the vibrational ground state (0000) and in the excited bending states ( v 6 v 7 v 8 v 9)=(1000), (0100), (0010), and (0001). Pure rotational transitions J+1← J were recorded in the ranges 40–120 and 240–315 GHz. The analysis of the spectra, aided greatly by accompanying ab initio calculations, yielded precisely determined rotational, centrifugal distortion, and l-type doubling constants. They are in excellent agreement with the results of coupled-cluster calculations. Wavenumbers and infrared (IR) intensities of various stretching vibrational transitions were calculated variationally. Good agreement with results from high-resolution IR spectroscopy is observed for the highest fundamentals ν 1– ν 3, with deviations amounting to 15.4 cm −1 ( ν 1), 1.2 cm −1 ( ν 2), and 7.0 cm −1 ( ν 3).

Methodology for Deriving Deep-Layer Mean Temperatures from Combined Satellite Infrared and Microwave Observations

Abstract Deep-layer mean temperatures from Microwave Sounding Unit (MSU) observations have been used by scientists to study trends and interannual variations of tropospheric and lower-stratospheric temperature. The spatial resolution of MSU deep-layer mean temperatures is rather poor for studying trends in localized regions. A method is developed in which infrared observations from the High-resolution InfraRed Sounder (HIRS) is used in combination with MSU to derive deep-layer mean temperatures with improved vertical and horizontal resolution. Even though the relationship between infrared radiance and temperature is not linear, the layer associated with the mean temperature is shown to be well defined with a small airmass dependency that is similar to MSU’s airmass dependency. Preliminary validation of HIRS–MSU-derived layer mean temperatures with radiosonde layer mean temperatures show similar precision when compared to MSU-only derived temperatures.

Methodology for Deriving Deep-Layer Mean Temperatures from Combined Satellite Infrared and Microwave Observations

Deep-layer mean temperatures from Microwave Sounding Unit (MSU) observations have been used by scientists to study trends and interannual variations of tropospheric and lower-stratospheric temperature. The spatial resolution of MSU deep-layer mean temperatures is rather poor for studying trends in localized regions. A method is developed in which infrared observations from the High-resolution InfraRed Sounder (HIRS) is used in combination with MSU to derive deep-layer mean temperatures with improved vertical and horizontal resolution. Even though the relationship between infrared radiance and temperature is not linear, the layer associated with the mean temperature is shown to be well defined with a small airmass dependency that is similar to MSU’s airmass dependency. Preliminary validation of HIRS–MSU-derived layer mean temperatures with radiosonde layer mean temperatures show similar precision when compared to MSU-only derived temperatures.

Methanol Laser Line Assignments: Evidence of Four-Level Laser Systems

The “Ritz” computer program, developed for facilitating the assignment of molecular Fourier transform absorption spectra and described in a previous work, determines the energy level values involved in the assigned transitions by the Rydberg–Ritz combination principle. Combining the data obtained from the analyses of high-resolution infrared (IR) and far-infrared (FIR) spectra, it is possible to predict possible FIR laser emissions of molecules. In the present work we have applied this method to the common isotopomer methanol,12CH316OH, and obtained 14 proposed assignments for previously unassigned FIR laser lines. We also predict 15 possible new FIR laser emissions. For the first time, an assignment involving a four-level laser system with collisional population transfer to a slightly higher energy level is reported.

Accuracy of total ozone column amounts observed with solar infrared spectroscopy

Total ozone column amounts were observed at Rikubetsu (43.5°N, 143.8°E), Japan on 90 days between May 18, 1995 and April 26, 1996 with a high‐resolution infrared (IR) Fourier transform spectrometer and compared with Dobson spectrometer measurements. The sensitivities of the analysis for IR solar absorption spectra to initial profiles were examined using two kinds of initial profiles for ozone and temperature, namely monthly and yearly averages. IR/Dobson mean column ratios in the two cases were 1.02 and 1.03 and the standard deviation of the ratios were 3.7 and 4.1%, which correspond to 14 and 16 Dobson Units. The standard deviations are smaller than or comparable to the amplitudes of the day‐to‐day total ozone column variations indicating that day‐to‐day variations can be detected using monthly or yearly averaged profiles. However, significant solar zenith angle (SZA) dependences were observed in the columns derived using yearly averaged profiles. The SZA dependence was most significant in January and February when the ozone amount in the lower stratosphere was largest. The SZA dependence is considered to be caused by the difference between initial and actual ozone profiles.

The low-energy thermal excitation spectrum of nitrogen molecules adsorbed on Ni(110): Implications for molecular adsorption sites

The adsorption of N2 molecules on Ni(110) has been investigated by high-resolution He-atom energy-loss spectroscopy. Two external vibrations in the subthermal (< 30 meV) energy regime at 5.75 and 4.5 meV have been observed and are shown to imply the existence of two different adsorption sites, which are assigned to an on-top and a bridge-site. This finding is at variance with the interpretation of data from electron energy loss spectroscopy and InfraRed (IR) spectroscopy, where only one mode of the internal stretch vibration v1 at frequencies is observed for the chemisorbed nitrogen molecules. A reanalysis of previously published high-resolution IR data reveals that the presence of the second unexpected adsorbate species correlates with a feature in the IR spectra, which previously has been assigned to N2 molecules adsorbed at defect sites. These findings reveal that in this case the external vibrations are significantly more sensitive to different adsorption sites than the internal vibration, the latter exhibiting a difference between on-top and bridge sites of less than 6 cm−1.

Infrared microscopy studies on high-power InGaAs-GaAs-InGaP lasers with Ga/sub 2/O/sub 3/ facet coatings

InGaAs-GaAs separate confinement, heterostructure single quantum-well (SCH-SQW) lasers (/spl lambda/=0.98 /spl mu/m) with lattice-matched InGaP cladding layers, using a new Ga/sub 2/O/sub 3/ low reflectivity (LR) front-facet coating, are reported. The CW peak power density (17 MW/cm/sup 2/) of 6 /spl mu/m/spl times/750 /spl mu/m ridge-waveguide lasers is limited by thermal rollover, and repeated cycling beyond thermal rollover produced no change in operating characteristics. The high-power temperature distribution along the active stripe has been measured by high-resolution infrared (3-5 /spl mu/m) imaging microscopy. The temperature profile acquired for a very high optical power density P/sub D/=11 MW/cm/sup 3/ was found to be uniform along the inner active laser stripe, and revealed a local temperature increase at the LR front facet /spl Delta/T/sub f/ of only 9 K above the average stripe temperature /spl Delta/T/sub s/=24 K. An excellent front-facet interface recombination velocity <10/sup 5/ cm/s has been inferred from the measured low local temperature rise in the front facet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of aircraft exhaust emissions and infrared spectra for remote measurement of nitrogen oxides

Abstract. Infrared (IR) molecular spectroscopy is proposed to perform remote measurements of NOx concentrations in the exhaust plume and wake of aircraft. The computer model NIRATAM is applied to simulate the physical and chemical properties of the exhaust plume and to generate low resolution IR spectra and synthetical thermal images of the aircraft in its natural surroundings. High-resolution IR spectra of the plume, including atmospheric absorption and emission, are simulated using the molecular line-by-line radiation model FASCODE2. Simulated IR spectra of a Boeing 747-400 at cruising altitude for different axial and radial positions in the jet region of the exhaust plume are presented. A number of spectral lines of NO can be identified that can be discriminated from lines of other exhaust gases and the natural atmospheric background in the region around 5.2 µm. These lines can be used to determine NO concentration profiles in the plume. The possibility of measuring nitrogen dioxide NO2 is also discussed briefly, although measurements turn out to be substantially less likely than those of NO. This feasibility study compiles fundamental data for the optical and radiometric design of an airborne Fourier transform spectrometer and the preparation of in-flight measurements for monitoring of aircraft pollutants.

Assignments and Predictions of Optically Pumped Far-Infrared Laser Lines in [13C] Methanol and Associated High-Resolution Spectra

In this work, the high-resolution infrared (IR) spectrum of 13C-substituted methyl alcohol corresponding to the C-O stretch vibration and the far-infrared (FIR) spectrum corresponding to the torsional-rotational transitions have been recorded using a Fourier transform spectrometer. The results of detailed analyses of the spectra have been applied to propose new assignments of FIR laser lines pumped by the 9 P(34)CO2 laser line. These assignments involve highly perturbed levels in the first excited C-O stretch vibrational state. The assignments are supported by closed combination loops of accurately measured IR and FIR transitions. The analysis also yielded accurate frequencies for 17 potential FIR laser lines in [13C] methanol. The spectral data relevant to this work are presented. The FIR absorption spectroscopic study allowed us to evaluate the leading torsional-rotational molecular parameters for 13CH3OH in the vibrational ground state. The results of the high-resolution study will be useful for a precise model of the Hamiltonian for the excited C-O stretching state.