Showing papers on "Transmittance published in 1985"

Optical Properties of Aluminum Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering

Abstract: The detailed study of optical transmittance and reflectance in Al-doped ZnO thin films prepared by rf magnetron sputtering is described. Films obtained with Al2O3 content up to 10 wt% showed an average transmittance above 85% in the visible range. The absorption edge was blue-shifted with increasing carrier concentration. The shift was interpreted to be a result of competition between many body effects and the Burstein-Moss effect. It is shown that films obtained with an Al2O3 content of 1–2 wt% can achieve an excellent IR shielding.

Electroless deposition of cadmium stannate, zinc oxide, and aluminum‐doped zinc oxide films

Abstract: Transparent conducting films of cadmium stannate (Cd2SnO4), zinc oxide, and aluminum‐doped zinc oxide have been made by a simple, economical electroless deposition technique. The as‐deposited films of cadmium stannate have a 75% transmittance in the visible, 48% reflectance in the IR, and a band gap of 2.7 eV. Its resistivity is ∼10−1 Ω cm. Vacuum annealing changes the transmittance in the visible range to 82%, the IR reflectance to 62%, and the band gap to 3.1 eV. The corresponding values for the hydrogen‐annealed films are 87%, 76%, and 3.2 eV. Annealing lowers the resistivity of the films to ∼10−2 and ∼10−3 Ω cm for vacuum and hydrogen‐annealed films, respectively. The undoped zinc oxide films have transmittance in the visible and reflectance in the IR of 80 and 67% respectively. Aluminum doping increases the transmittance to 88% and reflectance to 83%. The optical band gap of undoped and aluminum‐doped zinc oxide films are found to be 3.40 and 3.98 eV, respectively. The resistivity is 1.20×10−2 and 6....

Spectral transmittance and contrast in breast diaphanography.

Abstract: Diaphanography is an imaging technique using transillumination with visible and near‐infrared radiation, and a video camera, to diagnose breast disease, including cancer. Originally based on luminance contrast only, there is now interest in false‐color multispectral imaging in selected spectral bands to improve tissue differentiation. Some success has been achieved, but the scientific basis for the results was unknown. This research is concerned with measurements of the diffuse transmittance of breast tissues as a function of wavelength in the 600–1060 nm range (and calculations of contrast with a one‐dimensional diffusion theory model).Carcinoma and glandular tissues were found to have similar spectral transmittances with an increase in transmittance between 750 and 900 nm, and an absorption window around 960 nm. Adipose tissue showed a distinct transmittance minimum at 930 nm. I n v i v o measurement of an intact normal breast showed a minimum at about 825 nm, as yet unexplained. The transmittance data and reflectance data were used to derive the scattering and absorption coefficients. The diffusion length was also determined from radiance versus depth measurements. These coefficients were used for calculations of contrast in a one‐dimensional slab model, with and without a layer of cancerous tissue positioned between two slabs of normal tissue.

Experimental requirements for quantitative mapping of midgap flaw concentration in semi‐insulating GaAs wafers by measurement of near‐infrared transmittance

Abstract: The experimental properties are critiqued that relate the midgap flaw concentration in semi‐insulating GaAs, and the resulting near‐infrared transmittance of a polished wafer. Since quantitative information of such flaw concentrations is desirable even for an optical thickness αt≪1, a highly stable and accurate experimental arrangement is described, which permits a meaningful evaluation even when αt≂0.01. (The transmittance is then almost Tmax, as set by the substantial reflectance losses.) This system permits mapping over a wafer’s area, by translation of the wafer with respect to the optical path. Calibration of absorption into flaw concentration is discussed for the midgap EL2 donor defect, and (in an appendix) for chromium‐doped GaAs. Representative wafer maps for EL2 are used as illustrations, some as mosaic grey‐scale matrix plots, and others as pseudo‐three‐dimensional contour plots.

Infrared reflection properties of five types of black coating for radiometric detectors

Abstract: An ideal coating for a radiometric detector should have a low reflectance which is independent of wavelength and of angle. These properties have been investigated using specially developed equipment. A diffuse reflectometer/transmissometer at NPL has been designed to determine the spectral variation of these quantities, irrespective of whether the sample has a regular component of transmittance. This facility has been used to measure the total, regular and diffuse reflectances of five types of coating for radiometers. A polar scattering facility at Sira using 10.6 mu m radiation has been used to investigate the angular reflection properties of the coatings. Results from both techniques show that coating thickness can be critical for adequate performance, and that some types of particulate metal coating are not very reproducible in their properties.

Hole burning, Stark effect, and data storage

Abstract: This paper investigates the effects of an external electric field on hole-burning processes. The photoprocess for hole burning involves the transformation of chlorin (dihydroporphyrin) into its phototautomer. Two-dimensional representations (voltage/frequency) of the transmittance and the change in optical density are illustrated for single and multiple hole burning. At 4.2 K a hole width of 25 kV/cm in electric field scanning range and of 3 GHz (0.1 cm−1) in optical frequency was achieved. The increase in the data storage capacity for optical memory devices offered by the electrical field parameter is discussed.

Light-pressure bistability at microwave frequencies

Abstract: Evidence of bistability induced by radiation pressure in a system operating at millimeter bandwidth is presented. The transmittance of a microwave cavity equipped with a movable mirror becomes bistable under the variation of two control parameters: the incident field intensity and the incident field frequency. Good agreement between theory and experiment has been achieved.

Submillimeter and millimeter wave characterization of absorbing materials.

Abstract: Several microwave absorbers have been characterized in terms of transmittance and reflectance at frequencies between 35 GHz and 3 THz. The materials studied were a series of iron-loaded cast epoxy absorbers known as Eccosorb. Measurements show that reflectance and absorption coefficient increase with the iron density. A dramatic decrease, by as much as a factor of 2, in absorption coefficient was observed when the samples were cooled from ambient to cryogenic temperatures. A blackbody calibrator to be operated at liquid helium temperature was constructed using the measured optical constants for these absorbers. The measured absorption coefficient for cold Eccosorb CR-110 is within 20 percent of that reported recently by Peterson and Richards.

Characterization of growing thin films by in situ ellipsometry, spectral reflectance and transmittance measurements, and ion‐scattering spectroscopy

Abstract: A versatile ultrahigh‐vacuum thin‐film deposition and analysis system is described. Films are deposited by electron beam evaporation with the possibility of ion beam bombardment of the growing film. Measurements of the reflectance and/or transmittance of the coating surface can be made simultaneously at 16 wavelengths across the visible or infrared spectrum. Ellipsometric measurements can also be made in situ, at a single wavelength and single angle of incidence, by an ellipsometer which can operate in either an automatic rotating analyzer mode or a manual nulling mode. The system is also equipped with an ion gun producing a submillimeter spot, and with a hemispherical sector, ion energy analyzer for ion scattering spectroscopy studies of the film surface. Results obtained during the deposition of a gold film are presented to demonstrate the capability of the system.

Narrow band selective absorption filter

Abstract: A solid state form of a dye-solution absorption filter is disclosed. Physical vapor depositable (i.e., evaporable) dyes are codeposited with a polyester matrix in a vacuum system to randomly disperse dye molecules in a solid dilutant. The dyes are selected to absorb at the wavelengths of interest. Dilution in a transparent matrix affords narrow band absorption and good out of band transmittance. Multilayer configurations allow absorption of a plurality of wavelengths. The filter coating conforms to curved and sharply contoured surfaces and layers only 10 microns thick afford very high absorptance.

Atmospheric transmittance from spacecraft using multiple view angle imagery

Abstract: A procedure for determining atmospheric transmittance using surface images acquired at several view angles from space is presented. Fourier filtering of the image data is used to mitigate the effects of atmospheric path radiance and instrument noise. Although it is essential for some contrast to be present in the images, knowledge of the atmospheric scattering phase function or the surface bidirectional reflectance function is not required. The method appears to provide absolute transmittances with an accuracy of better than 10 percent, which is useful in some applications.

Transparent and infrared-reflecting indium-tin-oxide films: quantitative modeling of the optical properties.

Abstract: A quantitative theoretical model for the radiative performance of heavily n-doped semiconductors is presented. It embraces the combined effects of valence electrons, free electrons, and polar optical phonons. The model is applied to indium-tin-oxide films and is used to compute integrated luminous, solar, and thermal properties. Optimization of film thickness and electron density can yield single uniform coatings on glass with 78% normal solar transmittance and 20% hemispherical thermal emittance.

Physical properties of chemically sprayed tin oxide and indium tin oxide transparent conductive films

Abstract: Optical and electrical properties of transparent conductive oxide films of undoped and doped SnO2 and In2O3 prepared using the pyrolysis spray method were studied. The optical constants extracted from transmittance and reflectance measurements between 0.25 and 3 mu m are interpreted to give values of the direct allowed band gap (4.54 eV for SnO2:F and 3.80 eV for ITO) and the indirect forbidden band gap (2.77 eV for SnO2 and 2.90 eV for ITO). Typical SnO2:F and ITO films present high transmission ( approximately=85%) and resistivities of about (9*10-3-5*10-4) Omega cm and 10-1 Omega cm respectively. Suitable figures of merit allow a useful comparison to be made of the physical properties of the different films.

Analyses of PLZT Electrooptic Shutter and Shutter Array

Abstract: The driving voltage and light transmittance in PLZT transverse electrooptic shutters composed of interdigital electrodes are investigated theoretically, with the electrode width, electrode gap, and wafer thickness being treated by the finite-element method. A new structure consisting of a combination of metal and transparent electrodes is presented, giving improved transmittance and driving voltage. Furthermore, the finite-element method is used to investigate the optimum driving voltage, fluctuation in light intensity, and S/N ratio in a one-dimensional optical shutter array. The combination of metal and transparent electrodes also brings about a low driving voltage, high transmittance and high S/N ratio in the shutter array.

Determination of the optical constants of a thin film from transmittance measurements of a single film thickness.

Abstract: A subtractive Kramers-Kronig method is presented for obtaining the optical constants, n and k, of a uniform absorbing film on a substrate using the transmittance spectrum of a single film thickness. We give the results of tests on the reliability of our method, demonstrate the usefulness of the method when only transmittance data are available, and give examples of thin films whose optical constants depend on their thickness.

Polymer-polypyrrole alloy films as semitransparent organic conductors

Abstract: The electrochemical polymerization of pyrrole on a polymer‐coated electrode produces an electrically conducting polymer‐polypyrrole alloy film. The surface resistance and the optical transmission of the alloy film can be controlled by the polymerization conditions, and semitransparent conducting films with a transmittance of 60% and a conductivity of 2/Ω cm can be realized.

Reflection and transmission for gyroelectromagnetic biaxial layered media

Abstract: A planar structure consisting of layers of different media is considered. The material of each layer is linear and homogeneous but anisotropic and, in general, exhibits biaxial, gyroelectric, and gyromagnetic properties. Thus most materials used in practice fall into the general category considered here. The structure has free space on one side and an isotropic medium (e.g., a dielectric or a metal) on the other side. A plane electromagnetic wave with arbitrary direction and polarization is incident upon the structure. The propagation constants and the components of the electric and magnetic fields are determined in each layer. A chain-matrix approach is implemented to obtain reflection and transmission coefficients for the structure.

Analysis Of Spectrally Selective Liquid Absorption Filters For Hybrid Solar Energy Conversion

Abstract: Various techniques have been proposed to convert solar energy to both electric power and heat in hybrid systems. Many of these approaches are designed to utilize spectral selectivity to improve the overall conversion efficiency. Examples include spectrally selective beamsplitters and arrangements of long-wave or short-wave-pass glass filters that divide the spectrum so that photon energies are roughly matched to the energies corresponding to the solar-cell bandgaps or to efficient photothermal convertors. This paper describes the analysis of liquid optical filters that have high transmittance in the visible spectrum and high absorptance in the infrared. These qualities make it possible to capture that portion of the spectrum useful to a quantum convertor, such as a photovoltaic cell, while channeling the "excess heat" of the photons with energies below the bandgap to a thermal convertor, thereby enhancing the overall conversion efficiency of the system. The preliminary studies show that spectral responses of the tested solutions (salts in water) are primarily influenced by the cation component of the salt solution. By changing the solutions and concentrations, a variety of spectrally selective filters can be tailored to match system requirements.

Neutron transmission properties of perfect silicon crystals

Abstract: Silicon crystals are of interest as filter material for thermal neutron beams. For this reason the total cross-section has been determined as a function of temperature for neutron energies ranging from 22 × 10−4 eV to 50 eV. Whereas cooling the filter to 77 K considerably improves the transmittance for thermal neutrons a further decrease in temperature has only a minor effect. The observed cross-section is well described by a treatment of thermal diffuse scattering based on the Debye approximation. Precise values of σabs and σfree are given and compared to literature.

Experiment and theory of ‘transparent’ metal films

Abstract: We report here the optical properties of near-transparent porous platinum films supported on p-type indium phosphide (InP). The deposition of small quantities of catalytically active metals on p-InP increases photoelectrochemical solar-to-hydrogen conversion efficiency by providing a pathway for photogenerated electrons to reduce efficiently protons in solution1. Surprisingly, efficiencies increase slowly even after fairly thick metallic layers have been deposited. These results imply that in certain conditions the metal overlayer is effectively transparent to the incident light, or even promotes the coupling of incident radiation into the bulk of the semiconductor2. We present here both experimental and theoretical evidence to show that these effects can be understood in terms of microstructure: when the metal films are sufficiently porous and built up from particles smaller than the wavelength of the transmitted light, the photon fields are screened out of the metal phase and are forced into the void structure. This increases the effective refractive index of the layer over that of the ambient and provides a better match with the substrate, while incurring negligible absorption loss.

Optical properties of thin films on rough surfaces: II. Long correlation length limit; comparison with earlier work

Abstract: The general theory, of second order in the film thickness and surface roughness over the wavelength, developed in an earlier paper on the optical properties of thin films, is applied in the limit that the correlation length of the surface roughness is much larger than the wavelength of light. The reflectance, transmittance and ellipsometric coefficient are calculated in this limit and the results are compared with those obtained by Ohlidal and co-workers in the same limit. It is proved that the difference in results found is a direct consequence of the neglect of local curvature of the rough surface by these authors, which is an inconsistent approximation in the second order theory.

Spectral Transmittance Characteristics of Holmium Oxide in Perchloric Acid Solution.

Abstract: The work describes the methods and procedures used to determine the wavelengths of minimum transmittance of holmium oxide in perchloric acid solution. Measurements of spectral transmittance of the solutions were made by means of a high precision spectrophotometer over the wavelength range 200 nm to 680 nm. The wavelength scale accuracy of this instrument was verified by extensive measurements of mercury and deuterium emission lines. The measurements of spectral transmittance of the holmium oxide solutions were made as a function of temperature, purity, concentration, and spectral bandwidth. Analysis of the uncertainties associated with these parameters and the uncertainties associated with the calibration of the instrument wavelength scale and the data analysis have resulted in an estimated uncertainty of ±0.1 nm for the determination of the wavelengths of minimum transmittance of the holmium oxide solution.

Inductive grids in the resonant region: Theory and experiment

Abstract: We compare rigorous modal expansion methods with transmission-line models for the spectral properties of inductive grids. We compare the predictions of the former with measurements of grid transmittance, reflectance and phase angles as a function of wavelength. We show that the rigorous theory can accurately reproduce measured grid properties, both for normal and oblique incidence, and for both fundamental polarizations of incident radiation. We pay particular attention to the so-called “thickness dip”, an abrupt drop in transmittance which occurs for one polarization at off-normal incidence. We study the variation of $$\lambda _a$$ , the wavelength of the thickness dip, with grid parameters. We also study the variation of $$\lambda _m$$ , the wavelength of maximum transmittance, with grid parameters. We give four design rules which enable the optimization of grid parameters for use in multi-element filter stacks not relying on interference properties. We present a comprehensive set of curves showing the variation of spectral transmittance with grid aperture and thickness, for both fundamental polarizations and for a range of angles of incidence.

Nitrogen-broadened lines of ethane at 150 K☆

Abstract: Spectral transmittance has been measured in the nu9 fundamental band of C2H6 at 150 K using a Fourier transform spectrometer with apodized spectral resolution of 0.06/cm. Comparison of observed spectral transmittance with a line-by-line computation using the spectral catalog of Atakan et al. (1983) has yielded N2-broadened half-widths at 150 K.

Beam splitter for a wide-angle Michelson Doppler imaging interferometer.

Abstract: The design and construction of a hexagonal interferometer beam splitting prism is described in which the light falls onto the all-dielectric partially reflecting coating at an angle of 30° with respect to the normal. For a beam that undergoes one transmission and one reflection by the device, the average effective transmittance ½(T‖R‖ +T⊥R⊥) in the 0.55–0.75-μm spectral region is ∼0.23. This quantity is not strongly dependent on the plane of polarization of the incident light, nor on small changes of the angle of incidence from the design angle of 30°. Ways to improve further the performance of the beam splitter are indicated. Coating designs for other angles of incidence are also given.