Showing papers on "Transmittance published in 1989"

High-sensitivity, single-beam n(2) measurements.

Abstract: We present a simple yet highly sensitive single-beam experimental technique for the determination of both the sign and magnitude of n2. The sample is moved along the z direction of a focused Gaussian beam while the repetitively pulsed laser energy is held fixed. The resultant plot of transmittance through an aperture in the far field yields a dispersion-shaped curve from which n2 is easily calculated. A transmittance change of 1% corresponds to a phase distortion of ≃ λ/250. We demonstrate this method on several materials using both CO2 and Nd:YAG laser pulses.

Time resolved reflectance and transmittance for the non-invasive measurement of tissue optical properties.

Abstract: When a picosecond light pulse is incident on biological tissue, the temporal characteristics of the light backscattered from, or transmitted through, the sample carry information about the optical absorption and scattering coefficients of the tissue. We develop a simple model, based on the diffusion approximation to radiative transfer theory, which yields analytic expressions for the pulse shape in terms of the interaction coefficients of a homogeneous slab. The model predictions are in good agreement with the results of preliminary in vivo experiments and Monte Carlo simulations.

Light transport in tissue

Abstract: The propagation of light in tissue may be calculated by exact transport theory, or the approximate diffusion theory, provided the optical properties are known at the source wavelength. Optical properties for the exact methods are the absorption coefficient, scattering coefficient, and angular distribution of scattering. Appropriate properties for diffusion theory are the diffusion length and diffusion coefficient (corrected for anisotropic scattering). Computer programs and analytical solutions (for some simple geometries) exist, but the optical properties have to be determined experimentally and are not well defined as yet. The radiant energy fluence rate and the diffuse transmittance and reflectance have been measured in several tissues and in a few geometries, but there are gaps in the data as a function of wavelength. Calculations and measurements reveal that very large errors can result if the optical properties (for example, the diffusion length) are inaccurate, if anisotropic scattering is neglected, or if the finite size of the irradiating light beam is not taken into account. Furthermore, the radiant energy fluence and transmittance are perturbed by local regions of lesser or greater absorption, although recovery of the fluence and transmittance occurs beyond some three diffusion lengths.

Optical properties of rat liver between 350 and 2200 nm.

Abstract: Previous investigators have determined the optical properties of the liver at isolated wavelengths using various models of light propagation. In this study we derived coefficients for absorption, scattering, and anisotropy for rat liver between 350 and 2200 nm using measurements of integrated reflectance, transmittance, and on-axis attenuation and a diffusion approximation algorithm to solve the 1-D transport equation. These results were used to estimate the effective attenuation coefficient, penetration depth, and temperature rise induced by laser irradiation. The data should be of value to investigators in the field of tissue optics and developers of photomedical applications involving the liver.

Transmittance and reflectance in situ measurements of semicontinuous gold films during deposition

Abstract: We have continuously measured in situ reflectance and transmittance of percolating gold films over the entire range of surface coverage P, in the IR regime (1.7 and 2.2 μm). The samples present similar optical and electrical behavior, when compared on a normalized thickness scale. In the fractal region, close to the percolation threshold, the optical properties show a linear dependence on the surface coverage parameter, in agreement with a renormalization argument previously suggested. A strong absorption (about 40%), whose origin is not well understood, is found in the fractal region. The interpretations previously proposed by other authors are not applicable. We conclude that geometrical effects must dominate the optical properties over a large range of surface coverage.

Dual-pane thermal window with liquid crystal shade

Abstract: A dual-pane thermal window unit comprises two non-intersecting or, preferably, substantially parallel, spaced window panes, mounted in a window frame, a first of the panes having affixed thereto a first wall of an electro-optical liquid crystal cell providing a selected light transmittance, and a second of said panes delimiting, with a second wall of said cell, a space providing a thermal break. Each of the first and second walls comprises an electrically conductive film composed of plastic and having sufficient supporting strength to maintain the structural integrity of the cell. The window is light weight, economical to manufacture and efficient and reliable in operation.

Broad band nonreflective neutral density filter

Abstract: A broad band low reflectance neutral density optical filter. A neutral density filter having substantially flat transmittance and low reflectivity over a wide range of wavelengths from the ultraviolet through the visible region of the spectrum includes a transparent substrate, two successive layers of different dielectric materials on the substrate, at least two layers of metallic material, each metallic layer being separated from the preceding metallic layer by a layer of dielectric material, and finally, two succeeding layers of different dielectric mateials. The resultant neutral density filter thus has two layers of different dielectric materials between the substrate and the first layer of metallic material, and two layers of different dielectric materials between the atmosphere and the final layer of metallic material. This construction provides physical and spectral stability, relatively constant transmittance as a function of wavelength, and low reflectivity from both sides of the filter as a function of wavelength, which in turn permits a number of filters of the invention to be employed in series.

Aggregation states and electro-optical properties based on light scattering of polymer/(liquid crystal)composite films

Abstract: Electro-optical properties based on light scattering controlled by a.c. electric field were investigated for polymer/(liquid crystal) composite films. Scanning electron microscopic observation for the matrix polymer after extraction of LC with methanol exhibited that LC molecules were continuously embedded in a three-dimensional spongy network of polymer matrix. Such a membrane system with many optical interfaces plays an important role on light scattering without an imposed electric field. A high contrast of light-switching was observed; 3% transmittance of the as-cast composite film changed to 81% with the response time of 0.3 ms in the case of an applied 250 Vp-p a.c. electric field of 10 kHz at 333 K.

Angular‐selective optical properties of Cr films made by oblique‐angle evaporation

Abstract: Thin Cr films were made by oblique‐angle evaporation onto glass. Electron microscopy showed an inclined columnar microstructure. Spectrophotometry yielded a strongly angular‐selective p‐polarized transmittance, consistent with recent theoretical notions, of potential interest for energy‐efficient windows.

Neutral gray, low transmittance, nickel-free glass

Abstract: A neutral gray, low transmittance (less than 20 percent luminous transmittance) soda-lime-silica glass has reduced solar energy transmittance, and in particular exceptionally low ultraviolet transmittance (less than 20 percent total solar ultraviolet transmittance) when provided with the following colorant constituents: Fe 2 O 3 (total iron) 0.4-0.7 percent by weight FeO 0.08-0.15 Se 0.003-0.008 CoO 0.003-0.025 Cr 2 O 3 0.022-0.050 The glass avoids the use of nickel compounds as colorants. Parameters for melting such a glass in a commercial furnace are also disclosed.

Fiber optic application for thermal switching in vanadium dioxide films

Abstract: Large thermally induced changes in the end-interface reflectance and transmittance of silica fibers coated with vanadium dioxide films have been observed.

Electrical, crystallographic, and optical properties of ArF laser modified diamond surfaces

Abstract: Pulses of 193 nm radiation from an ArF laser with energies exceeding 0.5 J/cm2 have been shown to modify 40–60 nm thick layers of {100} and {110} oriented diamond surfaces. These layers exhibit highly anisotropic electrical and optical properties which have principal in‐plane axes along the 〈110〉 directions. The minimum resistance is (4–10)×10−4 Ω cm, and minimum in the optical transmittance and maximum in the reflectance occur when the electric field vector of the incident polarized light is aligned along the low resistance direction. Transmission electron microscopy indicates that the modified layer primarily consists of unidentified graphite‐like carbon phases embedded in diamond. The first‐order electron diffraction spots correspond to lattice spacings of 0.123, 0.305, and 0.334 nm. The modified layer is stable at 1800 °C, forms ohmic contacts to type IIb diamond, and supports epitaxial diamond growth.

Apparatus for heating a food item in a microwave oven having heater regions in combination with a reflective lattice structure

Abstract: An apparatus for heating a food item in a microwave oven is disclosed which has heater regions in combination with a reflective lattice structure. The combination of the reflective lattice structure and heater regions provides a food heating device which substantially maintains its reflectance, absorbance and transmittance during microwave heating. Substantial uniformity of heating is also achieved. The reflectance, transmittance and absorbance of the food heating device can be adjusted by changing the relative configuration and construction of the lattice structure and the heater regions.

Spectrally Selective Surfaces for Heating and Cooling Applications

Abstract: Heat transfer occurs via radiation, conduction and convection. When the radiative exchange is significant- which holds true for many important applications — one can achieve energy efficiency by exploiting surfaces with spectral selectivity. This term is taken to imply that the radiative properties (i.e. the absorptance A, emittance E, reflectance R, and transmittance T) are qualitatively different within different parts of the electromagnetic spectrum. Spectral selectivity is often obtained by use of coatings onto substrates which are either transparent or opaque metallic.

Transparent conductive film

Abstract: A transparent conductive film comprises, as the main component, indium oxide (In 2 O 3 ), and 6 to 20 mol % of zirconium oxide (ZrO 2 ). The film has a light transmittance of 90% or more and an electric resistivity of less than the 2×10 -4 Ω. cm of a conventional ITO film.

Thin-Film Optical Constants Determined from Infrared Reflectance and Transmittance Measurements

Abstract: A general method based upon reflectance and transmittance measurements in the infrared region has been developed for the determination of the optical constants n(v) and k(v) of thin films deposited on any substrate (transparent or not). The corresponding computer program, written in FORTRAN 77, involves three main parts: (1) a matrix formalism to compute reflection and transmission coefficients of multilayered systems; (2) an iterative Newton-Raphson method to estimate the optical constants by comparison of the calculated and experimental values; and (3) a fast Kramers-Kronig transform to improve the accuracy of calculating the refractive index. The first part of this program can be used independently to simulate reflection and transmission spectra of any multilayered system using various experimental conditions. Two practical examples are given for illustration. Simulation of reflection spectra at grazing incidence for thin films deposited on a metal surface and determination of the optical constants for thin CaF2 layers deposited on a silicon substrate are presented.

Near-ideal solar control characteristics of CuxS thin films

Abstract: CUxS thin films, deposited from chemical baths on glass substrates and air-annealed at 150 degrees C and then given a polymer protective coating, have been found to offer optical transmission and reflection characteristics near to ideal solar control characteristics. The transmission spectra in the visible region resembles the phototopic vision spectra, with an integrated transmittance of approximately=30%-providing a greenish-yellow illumination of the interior under daylight. The low integrated visible reflectance of approximately=9% prevents glare and the mild bluish-purple colour in reflected daylight improves cosmetic appearance. Due to the low sheet resistance of the films approximately=30 Omega Square Operator -1, the integrated infrared transmittance is very low, approximately=10% and the integrated infrared reflectance is acceptably high, 25%. The total optical and thermal transmittance into the interior through the CuxS coated glazing is in the 30-35% range, assuring substantial saving in the cooling costs when these glazings are employed in regions with a generally warm climate. Various possibilities in the commercial production of the coatings are suggested.

Nuclear reaction analysis of hydrogen in optically active coatings on glass

Abstract: Films of WO3, Ta2O5, SiO2 and indium tin oxide as well as combinations of such films were analyzed for hydrogen with the 15N technique. Such coatings are used in optical devices for controlling reflectance and transmittance. H content and its changes during storage and in coloration experiments are reported. Effects of ion irradiation are described.

New lowtran band model for water vapor

Abstract: A Transmittance band model for IR water vapor in the atmosphere is determined using line by line generated spectra. The absorberp arameters of the model are tabulated.

Ray model for transmission of metallic-dielectric hollow bent cylindrical waveguides.

Abstract: The problem of transmitting CO2 laser radiation through metallic or metallic with inner dielectric coating (metallic–dielectric) bent hollow cylindrical waveguides is investigated using a ray model. Computer calculations of transmission as a function of the geometrical dimensions of the waveguide are performed. The coupling of laser radiation at the entrance of the waveguide is also taken into account. The theoretical calculated transmission is compared with previously published experimental data and good agreement is obtained for a large range of curvatures. The devised ray model contributes to a better understanding of the role of the dielectric layer in the metallic–dielectric waveguide, increasing the transmission of the radiation. The calculation of the transmission as a function of the radius of the cross section of the waveguide shows that, for a best metallic–dielectric waveguide, an optimal cross-sectional diameter appears where the transmitted energy is maximum. The method presented will be of value as a tool in the design of hollow cylindrical waveguides.

Optical measurement of the refractive index, layer thickness, and volume changes of thin films

Abstract: Preparation, measurement, and calculation methods are discussed for the determination of the complex index of refraction, the layer thickness, and induced volume changes of thin layers (due to a phase change, for example). The principle of the calculation is fitting a curve in the reflectance–transmittance plane measured on a range of layer thicknesses, instead of fitting the reflectance and transmittance as a function of independently measured layer thicknesses. This general method is applied to thin films of GaSb and InSb, in which a laser-induced amorphous-to-crystalline transition can be used in optical recording. The information essential for optical recording applications is measured quickly by making use of a stepwise prepared layer thickness distribution, while the complex refractive index and the layer thicknesses can also be calculated unambiguously.

Transparent conducting indium doped ZnO films by dc reactive S-gun magnetron sputtering

Abstract: Transparent conducting ZnO films have been prepared by modified S-gun reactive dc magnetron sputtering using an indium doped Zn target. Films with a resistivity of 1.08 × 10−3 Ω cm and average transmittance of over 80% in the visible region were obtained. The influence of indium content at the surface of Zn target on the resistivity and transmittance of ZnO films was investigated. Optical properties of ZnO films in the 0.2–2.5-μm range were modeled by the Drude theory of free electrons. The reflectance of ZnO films in the 2.5–26.0-μm region was calculated.

Wideband monitoring and measuring system for optical coatings

Abstract: A wideband system, controlled by an IBM PC/XT computer, has been established for monitoring and measuring optical coatings in vacuum. With supporting software, it is adaptable to various monitoring methods, which include using merit functions as criteria for terminating deposition, and the simultaneous display of transmittance functions T, ∂T/∂t, and ∂T/∂λ at a particular wavelength. It can also be used in the measurement of optical constants of dielectric layers in vacuum. The design considerations of the system are discussed, and experimental results are given.

Optical information recording medium

Abstract: PURPOSE:To eliminate the reading error of signals by changing the reflectivity or transmittance of brightness and darkness in correspondence to the frequencies of repetitive patterns of brightness and darkness. CONSTITUTION:The reflectivity or transmittance of brightness and darkness is changed in accordance with the frequencies of the repetitive patterns of brightness and darkness. The method for changing the reflectivity or transmittance of brightness and darkness includes a method of changing the reflectivity or transmittance of brightness and darkens by providing the bright and dark patterns of a fine structure to the respective same frequency parts of white and/or black, etc. The bright and dark width 15'-20' of the resulted signal waveforms can, therefore, be made the same as the original width 15-20 when said waveform are binarized by the certain threshold value. The signal reading error is thereby eliminated.