Showing papers on "Transmittance published in 1977"

Optical properties of aggregated noble metal films

Abstract: The optical properties of aggregated noble metal films have been studied in the spectral range from 0.35 to 1.0 μm. From the measurements of reflectance and transmittance, the effective optical constants were derived. These constants were then compared to those given by a model considering the films as formed by small rotational ellipsoids. In the model, the dipole/dipole interactions between particles have been taken into account together with the influence of the substrate. Careful measurements of film structures have shown that the assumptions concerning the size and shape of particles are reasonable. When p-polarized incident light is used, the resonance wavelength observed in the visible for the noble metal films is shifted to shorter wavelengths as the angle of incidence is increased.

The optical properties of amorphous and crystalline silicon

Abstract: The optical constants n and k of amorphous and crystalline films of silicon have been found from measurements of reflectance and transmittance at normal incidence over the wavelength range from 2500 to 500 nm, and extended to 300 nm by the method of measuring reflectances from the specimen itself and after depositing on it a thin layer of Ta2O5. This latter method has also been made of the effects of annealing on amorphous films. The measurements on single-crystal silicon have been compared with the results of others obtained by Kramers-Kronig analysis.

Direct and indirect two-photon processes in layered semiconductors

Abstract: Two-photon absorption measurements have been carried out in the layered compounds GaSe, Pb${\mathrm{I}}_{2}$, and GaS using single-wavelength excitation by a neodymium and a ruby laser. The absorption coefficient for direct interband transitions has been measured in all materials by the nonlinear transmittance method. Nonlinear photoconductivity measurements allowed the determination of a nonlinear absorption coefficient for indirect transitions in GaS and the determination of free-carrier lifetime in all three materials. The experimental results are compared with existing theories.

Spectrophotometer-digital data processing system for appearance measurements providing fast and accurate standardization, ease of use for different appearance measurements and fast response

Abstract: A combined scanning spectrophotometer-digital data processing system including a microcomputer is described for making appearance measurements. The instrument is comprised by an optical sensing unit and a signal processing unit. The optical sensing unit utilizes a simulated D65 light source lamp together with an 8 inch diameter integrating light sphere for use primarily in the diffuse polychromatic illumination of reflectance test specimens but which also is used with transmittance test specimens. Light leaves the sphere through a transmittance port in which a transmittance test specimen may be disposed in the case of transmittance measurements. The light sphere further includes a reflectance port for making reflectance measurement of a test specimen placed at the reflectance port. Light from the reflectance test specimen leaves the sphere through the transmittance port along a single light beam path which is directed onto a rotating variable interference filter wedge for isolating the individual wave lengths over the visible spectrum. Light level at each wave length is sensed by a silicon diode electro-optic detector whose output is converted to digital signal form and together with a wave length identification signal supplied from a shaft encoder rotated synchronously with the rotating variable interference filter wedge monochromator, is supplied from the optical sensor unit to the signal processing unit. The signal processing unit utilizes a preprogrammed microcomputer and an operator controlled keyboard to quickly and easily perform zero adjust and standardization corrections together with other second order effect corrections and derives output measures of true reflectance, true transmittance, tristimulus color values, color scale values and color difference values. A printer or other display device is connected to the microcomputer to print out or display the spectrophotometric data or other tristimulus or color scale values representative of the appearance characterstics of either a transmittance or reflectance test specimen.

Optical property measurement system and method

Abstract: In an illustrated embodiment, brightness, color, opacity and fluorescent contribution to brightness are measured by an on-line sensing head providing for simultaneous measurement of transmitted and reflected light. By measuring two independent optical parameters, paper optical properties of a partially translucent web are accurately characterized substantially independently of paper grade and weight. The instrument is designed so as to be capable of transverse scanning of a moving paper web on the paper machine, and so as to monitor desired paper optical characteristics with sufficient accuracy to enable on-line control of the optical characteristics of the paper being manufactured. Advantageously, several sets of reflectance and transmittance values based on respective common spectral response functions are sensed continuously and/or simultaneously during movement of the web.

An approximate equation for predicting the solar transmittance of transparent honeycombs

Abstract: An approximate equation is presented for predicting the solar transmittance of transparent honeycombs. The method accounts for scattering which occurs in such honeycombs by introducing diffuse components for both the reflectivity and transmissivity of the honeycomb wall. Required inputs to the equation are the optical properties of the honeycomb wall material, averaged over the solar spectrum. Methods of determining these properties are described. Although strictly applicable to a square-celled honeycomb, the equation should be approximately valid for hexagonal honeycombs as well. The equation is compared to the measured transmittance of a hexagonal-celled Lexan honeycomb with good results.

Comparative study of the electronic structure of noble-metal-noble-metal alloys by optical spectroscopy

Abstract: Transmittance and reflectance measurements have been performed between 0.5 and 6 eV on thin films of noble-metal-noble-metal alloys over the whole concentration range. Optical absorption clearly shows that these alloys are of two types: On the one hand, in Au-Ag and Au-Cu alloys, the absorption spectrum moves and modifies its shape gradually from a constituent to the other one; on the other hand, in Ag-Cu alloys, the absorption spectrum has essentially the shape of the matrix spectrum, with a supplementary absorption band due to impurities. This suggests that in the first case, the $d$ bands of the constituents strongly overlap, while in the second case they overlap only slightly. All these results will be discussed in the framework of existing theories: the coherent-potential approximation and the virtual-bound-state theory. Ordering effects in Au-Cu and clustering effects in Ag-Cu are also investigated.

Heater control system for liquid crystal device

Abstract: A twisted nematic liquid crystal device contains a liquid crystal material having dielectric anisotropy Δe which is positive for certain values of temperature and frequency of an electrical signal applied across the material and negative for other values of these parameters. The device includes a heater and a test area (separate from the display area of the device) at which transmittance of light is monitored by a heater control circuit. A test frequency chosen to give Δe≈0 at the minimum desired operation temperature of the device is applied across the test area and the light transmittance is monitored to assure that the temperature is high enough. When the temperature is too low, the heater element is automatically energized to increase the temperature of the liquid crystal device.

Variable density sunglasses comprising light polarizing elements

Abstract: Variable density spectacles comprising a pair of superposed iodine stained light polarizing elements, one of such elements being rotatable through an arc of less than 90 degrees to provide changes in the light transmitting functionality of the superposed elements; each of said elements having a light transmittance of from about 42 to 44 percent.

The determination of the optical constants of thin films from measurements of normal incidence reflectance and transmittance

Abstract: When the optical constants n and k of a thin film are calculated from the measured normal incidence reflectance and transmittance (R and T) by a successive approximation method, the results are complicated by multiple solutions and critical points of the equations R(n,k)=0 and T(n,k)=0 in the n,k plane. A method is given which enables the physical solution to be determined and which provides solutions in regions near the critical points where the successive approximation method is very inaccurate. The method, which combines Kramers-Kronig analysis of the transmittance data with the successive approximation method, is illustrated by results of measurements on an amorphous Mg-Sb alloy.

Selective absorption of solar energy in ultrafine chromium particles

Abstract: Ultrafine chromium particles prepared by evaporation in argon + air are found to be highly absorbing over the solar spectrum and highly transparent in the infrared. Such spectral selectivity is the distinctive feature of a coating in an efficient photothermal converter for solar energy. Optical transmittance through coatings with mass density ≲0.5 g/m2 agrees well with calculations based on the Maxwell‐Garnett theory, whereas coatings with larger mass density exhibit a transmittance too low to be directly reconciled with this theory.

Optical properties of aggregated lithium deposits

Abstract: Reflectance and transmittance of aggregated lithium deposits, prepared under static and dynamic ultrahigh vacuum, have been studied at normal incidence in the spectral range 1–6 eV. The structure of these deposits was determined in situ using a carbon film replication technique. It is shown that the optical conductivity exhibits peaks in the visible and infrared ranges, which are due to plasma resonance of the conduction electrons. In the uv range, the conductivity rises due to interband transitions. The particle size histograms show that deposits are made up of axially symmetrical ellipsoids. It follows that Maxwell-Garnett theory is inappropriate to describe the optical properties of granular lithium deposits. A generalized Maxwell-Garnett theory for ellipsoidal particles, which takes the interactions between particles into account, is used. Good agreement between experiment and theory is obtained.

Spectrophotometers with digital processing

Abstract: Monochromatic light emitted from a monochromator is split into two light beams. These light beams are detected by a photodetector and converted into corresponding electric signals after having been transmitted, respectively, through a sample to be analyzed and a reference placed in the respective beam paths. The signal corresponding to the light beam transmitted through the sample and the signal corresponding to the light beam transmitted through the reference are converted into digital signals which are subsequently stored in respective digital storages or memories. The signal corresponding to the light beam transmitted through the reference is compared with a value in a predetermined range. The resultant value is then converted into an analog signal for operating a sensitivity regulator thereby to adjust the sensitivity of the photodetector. Thus, the signal corresponding to the light beam transmitted through the reference (reference light signal) is so controlled as to lie in a predetermined range. From the digital signals stored in the digital memory, ratio between the sample light signal and the reference light signal is arithmetically calculated by a digital processor unit for determining the transmittance of the sample. Since the reference light signal is prevented from significant variation and the calculation of the signal ratio is effected on the basis of digital technique, the measurement accuracy is remarkably enhanced.

Spectrophotometer utilizing a solid state source of radiant energy having a controllable frequency spectra characteristic

Abstract: A solid state source of radiant energy having a characteristic frequency spectra with a high frequency cutoff ν co , which is a function of the applied voltage value. The source is a metal-insulator-metal tunnel junction wherein the insulator layer is relatively thin with respect to the metal layers and inelastic tunneling occurs. To facilitate output coupling to surface plasmon modes in the junction, the counter-electrode metal layer, from which the radiant energy is emitted, is roughened. One of the uses for the solid state source is as a light source of a spectrophotometer where the transmittance or reflectance band characteristics of a sample are determined by converting the photodetector current to its second derivative and correlating the second derivative with the applied voltage which is modulated over a predetermined range of amplitude values.

Low heat transfer, high strength window materials

Abstract: A multi-pane window with improved insulating qualities; comprising a plurality of transparent or translucent panes held in an essentially parallel, spaced-apart relationship by a frame. Between at least one pair of panes is a convection defeating means comprising an array of parallel slats or cells so designed as to prevent convection currents from developing in the space between the two panes. The convection defeating structures may have reflective surfaces so as to improve the collection and transmittance of the incident radiant energy. These same means may be used to control (increase or decrease) the transmittance of solar energy as well as to decouple the radiative transfer between the interior surfaces of the transparent panes.

In situ determination of the optical and electrical properties of thin films during their deposition

Abstract: An experimental arrangement is described for measuring in situ in a nearly continuous way the reflectance R and transmittance T near normal incidence, as well as the electrical DC resistance of thin films throughout their deposition and subsequent heat treatment. It is then possible to determine the effective complex dielectric constant epsilon and the electrical DC resistivity rho as functions of the mass thickness of the deposit and to follow their evolution during film growth. The possibilities of the method are demonstrated by an application to thin films of gold.

Differentiation by Spatial Filtering

Abstract: A simple procedure for generating filters to perform first- and second-order differentiation has been presented. The procedure is based on the dependence of the diffraction efficiency on the grating constant of a binary grating. The influence of the finite or zero transmittance of the central region of the filter and also of the finite size of the filter on the quality of differentiation has been studied. It is shown that false information is obtained when the sizeable central region of the filter has zero transmittance. The experimental results for first- and second-order differentiation are presented.

Ultraviolet radiation dosimeter

Abstract: A method for detecting, monitoring or measuring visible and ultraviolet radiation exposure wherein a liquid crystal element covered with a coating layer transparent to the radiation is placed in the path of the radiation to be monitored and then the shift of the spectral reflectance or transmittance of the element is measured, this shift being a measure of the radiation dosage. This shift may be measured using reference liquid crystal elements or a spectrophotometer or similar measuring devices.

Conditions of pressure scanning of a Fabry-Perot interferometer over a wide spectrum range.

Abstract: The association of a Michelson interferometer and a Fabry-Perot etalon enables the control of the displacement of the peaks of Fabry-Perot transmittance by pressure scanning through Michelson fringes counting. Assuming the variations of the refractive index of gas as a function of wavenumber, pressure, and temperature are known, we show that it is perfectly possible to compute the number of fringes to shift in order to position a chosen peak of Fabry-Perot transmittance for any point in the spectrum. These possibilities enable us to build a real spectrometer whose accuracy is better than 0.05 cm−1 in the whole visible range.

Optical Linewidth Measurements On Silicon And Iron-Oxide Photomasks

Abstract: Measurement of linewidths on silicon and iron-oxide photomasks is hampered by the dark banding which occurs along the edges. It is shown that this banding arises from the combination of low contrast and optical path difference introduced by the silicon or iron-oxide in conjunction with the partial coherence of the illumination. As previously shown in work with chromium-oxide photomasks, when the condenser numerical aperture is sufficiently less than that of the objective, an expression can be derived for the proper transmittance threshold for determining edge location. An expression is also derived for the linewidth error which would result from locating the edge at the center of the dark band. Theoretical and experimental results are compared.

Bandpass filters for use in the visible region

Abstract: A series of new filter glasses showing fairly symmetrical bandpass shapes has been developed. The transmittance curves with half-widths ranging between 58 nm and 168 nm cover the whole visible region. It seems that almost any desired peak transmittance wavelength can be obtained by compositional shifting. These new filters should find useful application in optics and filter radiometry.

The linear Fresnel lens solar concentrator: Transverse tracking error effects

Abstract: The solar concentration performance of a line focusing, flat base Fresnel lens in the presence of small transverse tracking errors was analyzed. Solar transmittance of the lens and focal plane imaging characteristics were evaluated. Transmission losses by reflectance and material absorption were also studied.

Measuring apparatus of transmittances

Abstract: PURPOSE:To convert the measured values of transmittances of exhaust gases of varying transmittance measuring distances, temperatures and pressures to the values under fixed standard conditions thereby comparing exhaust gases under varying conditions.

Nonlinear absorption of SF(6) at high infrared intensities and high pressures.

Abstract: An experimental study of the saturable absorption of SF6 at high pressure (up to 500 Torr) with high laser irradiance is presented. Experiments carried out at the P(28) line of the CO2 laser show a decrease of transmittance with increasing laser irradiance before bleaching sets in. This is explained by a theoretical model using a single rate equation. The decrease of transmittance is shown to be due to vibrational excitation, whereas bleaching is caused by rotational hole burning. Previous results on saturation behavior of SF6 at the P(16) line of CO2 reported by Armstrong and Gaddy are given a new interpretation using the present model.