High Absorption Region Research Articles

Temperature Uniformity in Water Films and Wet Paper Through Spectrally Selective Infrared Heating

Experimentally-derived radiant emissions from a near-greybody source, as well as a source with a narrow-band emission centered at 1.5 µm (both gas radiant burners), were used to calculate temperature distributions along the depth of water and wet paper (fiber–water suspensions) films. A grey emitter resulted in a wide temperature gradient through the film depth due to significant overlap of regions of high spectral emission with regions of high spectral absorption. The narrow-band emitting source succeeded in the goal of reducing the temperature gradient though the water film, though a significant percentage of radiant energy transmitted through the entirety of the film. Using numerical optimization, narrow-band spectral emission sources were calculated from Gaussian functions (3.8 µm for water and 1 µm for paper with 80% water) which improved temperature uniformity without high transmission radiation losses.

Modeling of the refractive index and extinction coefficient of binary composite films

Southwell's analysis of optical multilayers within the limits of very thin films has been extended to include absorption in the multilayer for predicting the effective values of the refractive index n(e) and extinction coefficient k(e) of mixed-composition binary homogeneous films over a wide spectral region, including the high-absorption (k > 10(-2)) region. It has been found that n(e) in general is a complicated function of the optical parameters (n(1), k(1), n(2), k(2)) and volume fractions (f(1), f(2)) of the component materials in a homogeneous layer, and the expression for n(e) becomes the same as that predicted by the Drude model in the spectral region where the layers are transparent. Moreover, according to the present analysis, the volume fractions of the product of the refractive index and the extinction coefficient of the component materials of a binary composite film are additive and the sum equals the product of the effective refractive index and extinction coefficient of the composite film.

Formation of multidomain structures in an optically bistable absorption system under the action of hyper-Gaussian light beams

It is shown that several longitudinal domains of high absorption are formed under certain conditions in an optically bistable element based on increasing absorption under the action of a hyper-Gaussian light beam. This is caused both by the transformation of the initial beam profile into a tubular distribution and by the diffraction of light by a nonuniform boundary of the region of high absorption. The analysis of dynamics showed the possibility of formation of quasi-stationary regions with high absorption, which exist during a certain time. These effects can lead to false data recording in three-dimensional optical recording systems.

Analysis of THz-wave surface-emitted difference-frequency generation in periodically poled lithium niobate waveguide

It was shown that the periodically poled LiNbO3-waveguide with period of poling λ≈λ/ng (λ is the wavelength of emitted THz-wave, ng is a refractive index corresponding to optical group velocity) emits THz-wave difference-frequency generation (DFG) in the direction normal to the surface of the planar waveguide. The 5% distinction between the manufactured and required periods of gratings results only in a small deflection (∼6°) of the output THz-beam from the normal direction. The dependence of DFG efficiency on mode size is analyzed. The output THz power at λ=150 μm is estimated as 2 mW, taking into account imperfections in coupling incident beams with guided modes. It was shown that the efficiency of THz-wave DFG in surface-emitting geometry is more than for collinear geometry in bulk crystal, especially in the high-absorption wavelength region.

Photoacoustic studies of Zn1−xBexSe mixed crystals: two-layer approach

Using the photoacoustic spectroscopy, the following composition-dependent material parameters of Zn1−xBexSe mixed crystals were determined: thermal diffusivity, optical absorption coefficient spectra in the region of high absorption and in the Urbach's edge region, the energy gap values and the thermal and compositional broadening of the absorption bands. The quality of the surface of the samples and its influence on the determination of these parameters was checked and discussed.

P wave attenuation structure in the fault area of the 1995 Kobe earthquake

The three‐dimensional (3‐D) P wave attenuation structure in the Kobe epicentral area is determined using aftershock records from the 1995 Kobe (Hyogo‐ken Nanbu) earthquake. Waveform data from both permanent seismic networks and portable stations, set up following the Kobe mainshock, were used. The observed P wave amplitude spectra were inverted for the spectral plateau value, the source corner frequency, and a frequency‐independent t* operator assuming an ω2‐type source model. The calculated t* operators were subsequently used for the computation of the 3‐D absorption structure using a 3‐D velocity model. Only high‐quality amplitude spectra were used for the estimation of reliable attenuation parameters, resulting in a final data set of ∼4100 t* operators. Two regions of high absorption were found in the upper part of the crust. One is below the northern part of Awaji Island and reaches down to a depth of 5 km. The other region, northeast of Kobe city, is along the Arima‐Takatsuki tectonic line and extends along the Rokko, Kashiodani, and Yamada Faults. It extends northward to the Hokusetsu‐Sanchi area. In both regions a high density of fault lineations is mapped, and high Poisson ratios are known. This suggests that partially saturated cracks cause the observed high attenuation.

Spray pyrolytic deposition and characterization of SnS and SnS2 thin films

The spray pyrolysis technique is employed to prepare thin films of SnS on glass substrates and SnS2 on glass as well as fluorine doped tin oxide (FTO) coated glass substrates. The pyrolysis temperatures of SnS and SnS2 are 350 °C and 275 °C, respectively. The films are found to be n-type semiconductors. The SnS thin film is amorphous, whereas the SnS2 shows polycrystalline structure and the calculated average grain size is 115 Å for SnS2 on glass and 324 Å on the FTO substrate. From an analysis of the high absorption region data a direct-allowed transition at 2.44 eV has been observed for SnS2. In the optical investigations of SnS layers an non-direct-allowed transition at 1 eV is revealed. The corresponding absorption coefficients near the fundamental absorption edge are ~2 × 104 cm-1 and 4.6 × 103 cm-1 for SnS2 and SnS thin films. The room temperature dark conductivity of SnS is of the order of 10-3 -1 cm-1 and 10-4-10-3 -1 cm-1 for SnS2 films. The corresponding photoconductivity values of SnS, SnS2 on glass and SnS2 on FTO are ten, four and two times higher than the dark conductivity.

Free electron laser lithotripsy: threshold radiant exposures.

To determine the threshold radiant exposures (J/cm2) needed for ablation or fragmentation as a function of infrared wavelengths on various urinary calculi and to determine if there is a relation between these thresholds and lithotripsy efficiencies with respect to optical absorption coefficients. Human calculi composed of uric acid, calcium oxalate monohydrate (COM), cystine, or magnesium ammonium phosphate hexahydrate (MAPH) were used. The calculi were irradiated in air with the free electron laser (FEL) at six wavelengths: 2.12, 2.5, 2.94, 3.13, 5, and 6.45 microm. Threshold radiant exposures increased as optical absorption decreased. At the near-infrared wave-lengths with low optical absorption, the thresholds were >1.5 J/cm2. The thresholds decreased below 0.5 J/cm2 for regions of high absorption for all the calculus types. Thresholds within the high-absorption regions were statistically different from those in the low-absorption regions, with P values much less than 0.05. Optical absorption coefficients or threshold radiant exposures can be used to predict lithotripsy efficiencies. For low ablation thresholds, smaller radiant exposures were required to achieve breakdown temperatures or to exceed the dynamic tensile strength of the material. Therefore, more energy is available for fragmentation, resulting in higher lithotripsy efficiencies.

Improvement of X-ray CT image quality by use of prior information

Most objects processed by industrial CT contain materials having a large ray-absorption coefficient (e.g., metal). In such cases, streak artifacts (SA) occur due to excessive X-ray attenuation. If a region having a large absorption coefficient is in a section to be examined, this affects the whole measurement. However, since the size, shape, material, and structure of an industrial object are known from its design information, this region can be treated separately. This paper describes an algorithm to reconstruct such a special region by using a sequential approximation. Since previously known ray-absorption coefficients are given to the rest of the region in the object, the influence of SA can be reduced. Computer simulations with several phantoms were carried out, and the proposed method was demonstrated to have a very significant effect. If the abnormal part is large, the effect of the method is degraded. However, it has been found that this degradation is suppressed by increasing the directions of ray projections. If regions of high absorption and low absorption are in a single region, the effect of image improving by the method is also degraded, but a solution of this problem has been found. © 1999 Scripta Technica, Syst Comp Jpn, 30(11): 67–76, 1999

Efficiency of stimulation of gaseous chemical reactions by a diffracted light beam whose energy is absorbed by vibrational transitions

Laser-induced reversible chemical reaction kinetics in a gas mixture with the absorption of light energy by molecular vibrational transitions is investigated by mathematical modeling. The influence of beam diffraction, the relaxation time of vibrational energy into heat, and the order of vibrational transition on the structure of the region of high absorption and on the propagation of switching waves is analyzed. The discussion applies to pulses having a duration much longer than the time of energy transfer between vibrational levels.

Mid-infrared reflectance of silicone resin coating on metal substrates: Effect of polymeric binders' absorption

This study examines the infrared reflectance of polymeric coatings of silicone resin, silicone modified alkyd resin, and alkyd resin on aluminum substrates. The Kubelka-Munk's two constants theory is applied to calculate the reflectance while considering the surface reflection. An integrating sphere, infrared spectroradiometer and blackbody source are utilized as the measurement systems. The extinction coefficients are determined and used to calculate the reflectances of coatings on aluminum. Coefficients in the mid-infrared region display the quantitative difference between the polymers' structure. Silicone content enhances the absorptance of the coating in the mid-IR region. The coefficients of miscible silicone resin/alkyd resin blends are determined as well. Comparing the measured and calculated reflectances reveals that the discrepancies in thinner coatings or at the IR transparent wavelength are higher and around 0.1. Such a discrepancy is owing to the polymers' non-scattering with absorption properties which affect the validity of the values involving internal reflectances considered in the model. The internal reflectance can be assigned a negligible value in the high absorption region and is also a variable depending on thickness and transparency.

Excitation spectrum of luminescence in a-Si:H/a-Si 3N 4:H multilayers

Fundamental absorption edge spectra of a-Si:H well layers with thicknesses of 13, 25, 50 and 400 Å in a-Si:H/a-Si 3N 4:H multilayers were obtained from 10 to 10 6 cm −1 from optical transmission and luminescence excitation spectra. The absorption coefficient of the well layer in the low absorption region was observed to agree with that of bulk a-Si:H while in the high absorption region it is much smaller compared with bulk a-Si:H for the quantum confinement of electrons in the thin well layer. The mobility gap of a-Si:H was expected to be about 2.2 eV from the fundamental absorption edge spectra.

Si [CSC]x[/CSC] Forbidden Emission in NGC 1068 and NGC 7469

This Letter presents the first observation of [Si X] emission in a celestial object other than the solar corona. The detected line at 1.430 μm is present in the spectra of both NGC 1068 and NGC 7469. The ionization potential of Si X is 401.4 eV, which makes this one of the highest ionization energy lines observed in active galactic nuclei. The line falls in a region of high telluric absorption that requires a fortuitous combination of redshift and abnormally dry observing conditions to observe.

Effect of composition on optical properties of co-evaporated Mn/SiO x , Cr/SiO x and Cu/SiO x cermet thin films

Optical absorption spectra of amorphous Mn/SiOx, Cr/SiOx, and Cu/SiOx cermet films, 300 nm thick, with compositions from 0 to 25 at% Mn, Cr and Cu, respectively, prepared by co-evaporation at 293 Kin vacuo have been investigated. The linearity of (αħω)1/2 versusħω graphs in the high absorption region for all the cermet films indicates that indirect photon transitions in k-space are involved in the absorption process. Taue's rule is also confirmed. In all cases the optical energy gap decreases significantly with increasing metallic content of the films and the width of the tail of localized states increases.

Optical-constant calculation over an extended spectral region: application to titanium dioxide film

An iterative algorithm has been developed that takes starting values derived by an envelope method but then minimizes the influence of the envelopes and emphasizes the actual measured data. This combination avoids the difficulties inherent in the accurate drawing of the envelopes and makes it possible to extract the thickness and the optical constants of semiconducting and dielectric films over a wide spectral region, including regions of high absorption.

Optical absorption spectra of liquid sulphur over a wide absorption range

The optical absorption coefficient alpha of liquid sulphur has been measured in a wide absorption range from 5.5*10-2 to 2*105 cm-1 at temperatures from 130 to 450 degrees C. For measurement in the high-absorption range beyond 105 cm-1, we have developed an optical cell of our own design with a sample thickness of about 3000 AA. It was found that the absorption spectra are substantially changed at the polymerization temperature, especially in the high-absorption region; a new absorption band appears at around 3.25 eV and increases with increasing temperature. We discuss the origin of this new absorption band in the high-absorption region together with the details of the spectral changes in the intermediate and low-absorption regions.

Absorption Coefficient and Sensitivity of Positive and Negative Resists in the Vacuum Ultraviolet Region

Absorption coefficients for the resist materials (polymethyl methacrylate (PMMA) and partially chloromethylated polystyrene (CMS-DU)) were obtained in the vacuum ultraviolet (VUV) region. Negative and positive resist characteristics were investigated using a coherent VUV radiation source (λ=110-150 nm) generated by two-photon resonant four-wave mixing in Cd vapor. A very low exposure energy of approximately 1 mJ/cm2 was realized by employing a very thin resist film and using VUV light from the high-absorption region of the resist materials.

Near-infrared spectroscopy of the planetary nebula NGC 6572

view Abstract Citations (19) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Spectroscopy of the Planetary Nebula NGC 6572 Rudy, Richard J. ; Rossano, George S. ; Erwin, Peter ; Puetter, R. C. Abstract Spectroscopy of the PN NGC 6572 in the wavelength region 0.77-1.33 micron is presented. The measurement of line fluxes in regions of high telluric absorption is discussed, and an error in the wavelengths of forbidden P II reported in the literature is pointed out. The NGC 6572 continuum is well-matched by bound-free, free-free, and two-photon components at a temperature of 10,500 K. No significant contribution from the exciting star or hot dust is seen. The primary generation mechanism for the O I lines is fluorescent excitation by the stellar continuum. A sulfur abundance of 6.53 is derived, and N(P+)/N(S+) = 0.11 is found. This is much greater than the solar value and is probably due to the underabundance of S. Publication: The Astrophysical Journal Pub Date: February 1991 DOI: 10.1086/169711 Bibcode: 1991ApJ...368..468R Keywords: Infrared Spectroscopy; Planetary Nebulae; Stellar Spectra; Emission Spectra; Line Spectra; Near Infrared Radiation; Oxygen; Phosphorus; Sulfur; Astrophysics; INFRARED: SPECTRA; NEBULAE: INDIVIDUAL NGC NUMBER: NGC 6572; NEBULAE: PLANETARY full text sources ADS | data products SIMBAD (2)

Optical absorption spectra of fluid selenium near the nonmetal-metal transition region

The optical absorption coefficient of fluid Se was measured in the energy range of 0.5–4.5eV at temperatures up to 1700°C and pressures up to 500 bar. Measurements were made by use of quartz and sapphire cells. The optical path lengths were 5mm to 3000A, which enabled us to obtain the absorption coefficient in the wide range extending to the value of 2×10 5cm −1. The optical gap was for the first time derived derived from the analysis of the spectra in such a high absorption region. The optical gap substantially decreases with temperature and pressure eventually to vanish near the liquid-gas critical point.

Optical properties of zinc phosphide

The optical absorption edge of Zn3P2 has been measured by transmittance and photoconductivity at 300 K. The absorption coefficient in both polarizations is shown to follow the expected behavior for indirect gaps at 1.39 and 1.41 eV in parallel and perpendicular configurations. The high-absorption region has been measured in thin single crystals and the absorption coefficient is shown to agree with the optical constants derived from reflectivity for values of the absorption coefficient up to 105 cm−1. The optical properties and the behavior of photoconductivity are discussed in view of possible applications of Zn3P2 to solar energy conversion.