Showing papers on "Transmittance published in 1992"

Optical limiting performance of C60 and C70 solutions

Abstract: OPTICAL sensors used in connection with bright sources such as lasers and arc welders must commonly be protected from damaging light levels by the use of optical limiters1. One approach to optical limiting makes use of materials whose optical transmittance decreases at high light levels2–5. For most protective applications, the response must be rapid and the saturation threshold low; a lower threshold provides a greater safety margin. Studies of the optical properties of C60have shown that the absorption cross-section of the photoexcited triplet state is greater than that of the ground state6, suggesting that it may have a nonlinear optical response of the sort useful for optical limiting. Here we report measurements of the optical response of solutions of C60 and C70 in methylene chloride and toluene, using 8-ns pulses of 532-nm-wavelength laser light. We observed optical limiting behaviour in all cases, with saturation thresholds equal to or lower than those reported for other optical-limiting materials currently in use.

A new software tool for computing Earth's atmospheric transmission of near- and far-infrared radiation

Abstract: This report describes a new software tool, ATRAN, which computes the transmittance of Earth's atmosphere at near- and far-infrared wavelengths. We compare the capabilities of this program with others currently available and demonstrate its utility for observational data calibration and reduction. The program employs current water-vapor and ozone models to produce fast and accurate transmittance spectra for wavelengths ranging from 0.8 microns to 10 mm.

Nonlinear optical properties of carbon-black suspensions (ink)

Abstract: We performed a series of experiments on suspensions of carbon particles in liquids (ink) and carbon particles deposited on glass to determine the mechanisms for the observed optical-limiting behavior. Both materials show reduced transmittance for increasing fluence (energy per unit area). We found that nonlinear scattering dominates the transmissive losses and that the limiting is fluence dependent, so that limiters based on black ink are effective for nanosecond pulses but not for picosecond pulses. Additionally, the nonlinear scattering and the limiting behavior cease after repeated irradiation. For the liquid, flowing eliminates this effect. All the data obtained are consistent with a model of direct heating of the microscopic-sized carbon particles by linear absorption with subsequent optical breakdown initiated by thermally ionized carriers. A simple calculation gives temperatures higher than the sublimation temperature at the onset of limiting. Emission spectra measurements show singly ionized carbon emission lines with a hot blackbody background emission consistent with temperatures of ≃4000 K. A rapid expansion of the microscopic plasmas generated by the breakdown will effectively scatter further input light. Indeed, in time-resolved experiments the trailing portion of the pulse is most heavily scattered. The time-resolved transmittance of a weak cw probe beam also follows the temporal dependence of the singly ionized carbon emission (≃102 ns). We directly monitored the expansion of the scattering centers by angularly resolving the scattered light for different input fluences and fitting to Mie scattering theory. Since the carbon is black and the microplasmas are initiated by linear absorption, the limiting is extremely broadband. Within the context of this model we discuss the limitations and optimization of ink-based optical limiters.

Antireflection surfaces in silicon using binary optics technology

Abstract: Binary optics processing methods were applied to a silicon substrate to generate an array of small pillars in order to enhance transmission. The volume fraction of the silicon in the pillars was chosen to simulate a single homogeneous antireflection layer, and the pillar height was targeted to be a quarter-wave thickness. A mask was generated, using a graphics computer-aided design system; reactive-ion etching was used to generate the pillars. An improvement in long-wavelength infrared transmission is observed, with diffraction and scattering dominating at shorter wavelengths.

Scattering of electromagnetic waves by periodic structures

Abstract: The authors consider periodic structures made of spheres embedded in a host material with a different dielectric function. They show how to calculate the reflection and transmission of electromagnetic waves by a slab of the material parallel to a given crystallographic plane. The method of calculation is based on a doubling-layer scheme which obtains the reflection and transmission matrix elements for the multilayer from those of a single layer. The reflection and transmission characteristics of the slab are related to the complex band structure of the photon field associated with the given crystallographic plane of the corresponding infinite crystal, which is introduced in the manner of the low-energy electron diffraction theory. They present numerical results which demonstrate the applicability of the method to real systems of current interest and point out some interesting physics which arose from their calculations. They show in particular that the nondegenerate bands of the photon field at the centre of the surface Brillouin zone do not couple to the incident radiation, leading to total reflection at normal incidence.

Two integrating spheres with an intervening scattering sample

Abstract: Two integrating spheres placed so that the exit port of one and the entry port of the other are adjacent, with only a sample intervening, will permit the simultaneous determination of the reflectance and the transmittance of the sample. Such a geometry permits measurements to be made as the sample undergoes some external stimulation, such as heat, pressure, or a chemical change. To determine the sample reflectance and the transmittance from the measured values of irradiance within each sphere requires the calculation of the exchange of light through the sample between the spheres. First the power collected by a detector situated in the wall of an integrating sphere is calculated as a function of the area and the reflectance of the wall, the holes, the sample, and the detector for both diffuse and collimated light incident upon the sample and for a sample located at either the exit port (reflectance) or the entry port (transmittance) of the sphere. Next, by using the single-sphere equations, we calculate the effect of the multiple exchange of light between two integrating spheres arranged so that the sample is placed between them. In all the cases of two integrating spheres the power detected is greater than or equal to that for the single sphere and depends on both the reflection and the transmission properties of the sample. Additionally, the effect of a baffle placed between the sample and the detector or of a nonisotropic detector is to reduce the power detected.

Noise insensitive pulse transmittance oximeter

Abstract: A noise insensitive pulse transmittance oximeter (11) is disclosed. Two LEDs (21 and 23) are included in the pulse transmittance oximeter. The LEDs alternately emit a red light pulse and an infrared light pulse. A detector (13) detects corresponding red transmittance pulses and infrared transmittance pulses that are indicative of the amount of light transmitted through tissue having blood flowing therein. A microprocesser (29) determines the peak and valley values of the red transmittance pulses and infrared transmittance pulses over a cycle. The difference between the peak and valley values for the red transmittance pulses and infrared transmittance pulses are calculated by the microprocessor. The microprocessor generates control signals that vary the intensity of the LEDs until the differences between the peak and valley values of the red transmittance pulses and infrared transmittance pulses are substantially equal.

Method for forming laminate for microwave oven package

Abstract: A laminate structure useful for incorporating into a package structure for the microwave cooking of foodstuffs for consumption comprises an outer layer polymeric material, an outer layer of microwave transparent material, a grid layer having an electroconductive surface surrounding transmissive apertures located between the outer layers, and a thin layer of electroconductive material of sufficient thickness so that a portion of incident microwave energy is converted to thermal energy also located between the outer layers. The structure is useful in providing controlled surface heating and microwave transmittance to achieve a more uniformly heated product employing less structural material than the prior art.

Locally Weighted Regression in Diffuse Near-Infrared Transmittance Spectroscopy

Abstract: This paper presents an application of locally weighted regression (LWR) in diffuse near-infrared transmittance spectroscopy. The data are from beef and pork samples. The LWR method is based on the idea that a nonlinearity can be approximated by local linear equations. Different weight functions (for the samples) as well as different distance measures for “closeness” are tested. The LWR is compared to principal component regression and partial least-squares regression. The LWR with weighted principal components is shown to give the best results. The improvements with respect to linear regression are up to 15% of the prediction errors.

Liquid crystal Fabry-Perot etalon with glass spacer

Abstract: A tunable wavelength-selective filter includes a glass substrate, a transparent electrode layer, a highly reflective mirror, an alignment layer, a liquid crystal layer, another alignment layer, a transparent material layer whose refractivity index is substantially equal to that of the liquid crystal layer, another highly reflective mirror, another transparent electrode layer, and another glass substrate, which are stacked in this order. An etalon cavity of the filter includes two layers, the liquid crystal layer and the transparent material layer (such as a glass plate), which enables the cavity length to be increased without increasing absorption and scattering of the cavity. This makes it possible to narrow the FWHM, quicken the response time, and increase the transmittance of the filter. Applications for the filter include a double cavity structure tunable wavelength-selective filter of a wide tunable range, and a photodetector of a simple construction.

Transmission of kilowatt-class CO 2 laser light through dielectric-coated metallic hollow waveguides for material processing

Abstract: We have measured the transmittance of 3-kW CO2 laser light through Ge-coated Ag hollow waveguides. The basic characteristics such as transmissivity, bending loss, and output-beam properties are described. A maximum laser power of 2.6 kW was delivered through a straight hollow waveguide that was 1.7 mm in diameter and 2 m long. Furthermore, 4-m-long waveguides were fabricated by joining two waveguides.Finally, preliminary experiments on welding steel plates were done with the light transmitted through the waveguide. Although the focusing properties of the output beam should be improved for practical laser processing, this type of waveguide is promising for high-power CO2 laser-light transmission.

Optical properties of tin diselenide films

Abstract: SnSe2 films were deposited on substrates at 300 K by a conventional thermal evaporation technique. The as-deposited films were amorphous and transformed to the crystalline phase on post-deposition annealing above 573 K in an inert atmosphere. The optical properties of the films were investigated, using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 400–2000 nm. The refractive index data fit a single oscillator model with a dispersion parameter 5.149×10−14 and 5.773×10−14 eVm2 for the amorphous and crystalline films, respectively. The high-frequency dielectric constant of the amorphous films decreased from 9.871 to 7.475 for the crystalline films. The analysis of the spectral behaviour of the absorption coefficient in the intrinsic absorption region revealed an indirect forbidden and a direct allowed transition with energy gaps 0.99 and 2.05 eV for the amorphous films and 0.96 and 2.02 eV for the crystalline films, respectively.

Electrochromic-photovoltaic film for light-sensitive control of optical transmittance

Abstract: A variable transmittance optical component includes an electrochromic material and a photovoltaic device-type thin film solar cell deposited in a tandem type, monolithic single coating over the component. A bleed resistor of a predetermined value is connected in series across the electrochromic material and photovoltaic device controlling the activation and deactivation of the electrochromic material. The electrical conductivity between the electrochromic material and the photovoltaic device is enhanced by interposing a transparent electrically conductive layer.

Method and apparatus for comparing spectra

Abstract: In a method and a system for analyzing spectral data including a spectrophotometer and a spectral detector, a data station receives first transmittance spectrum data points and has a file register containing second transmittance spectrum data points. The first and second transmittance data points are transformed respectively to set of first and second absorbance spectrum data points. The first and second absorbance points are band pass filtered at a characteristic frequency nominally associated with spectral bandwidth so as to produce respective sets of first and second filtered data points. A set of weighting factors are established, each corresponding to the square of the sum of a first transmittance point and a second transmittance point for a selected frequency. A comparison factor is generated as a normalized sum of products over a selected spectral frequency range, each product being formed of a weighting factor and corresponding first and second absorbance data points for each selected spectral frequency.

A Soft X-Ray/EUV Reflectometer Based on a Laser Produced Plasma Source

Abstract: A soft x-ray reflectometer is described which is based on a laser-produced plasma source and is continuously tunable over the range 40 A < λ < 400 A. The source is produced by focusing 0.532-μm light from a Q-switched Nd:YAG laser on a solid target. The x-ray wavelength is defined using a high throughput spherical grating monochromator with moderate resolving power (λΔλ ≈ 100 to 500). A time-averaged monochromatized flux of more than 109 photons/s in a 1% bandwidth at 100 eV is obtained. Photon “shot noise” limited measurements are obtained by the use of an I0 detector to normalize out the shot-to-shot variations in source intensity. Measurements with submillimeter spot sizes are readily obtainable. Various detectors have been used and the advantages and disadvantages of each are discussed. The higher order contamination of the monochromator output has been analyzed using a second grating for the purpose of making measurement corrections. The reflectometer thus provides the capability for precision absolute measurements of the reflectance of gratings and multilayer mirrors, the transmittance of thin film filters, or other properties of x-ray optical elements.

UV-stabilized compositions and methods

Abstract: The present invention concerns compositions, which comprise a solvent, which is suitable for a medium of variable transmittance in a solution-phase electrochromic device, and a UV-stabilizer, which is an ester of 2-cyano-3,3-diphenyl acrylic acid. Among embodiments of the invention are solutions used as media of variable transmittance in electrochromic devices, especially single-compartment, self-erasing, solution-phase electrochromic devices. The UV-stabilizer provides to the compositions of the invention stability against degradation from exposure to ultraviolet radiation, including that from the sun. Among applications of electrochromic devices comprising solutions according to the invention are use as variable transmittance components in variable reflectance, outside, rearview mirrors for automobiles.

Tinted solution-phase electrochromic devices

Abstract: The invention provides improved solution-phase electrochromic devices, wherein the solution of reversibly variable transmittance is tinted with a tint-providing compound, and solutions of reversibly variable transmittance for use in the improved devices of the invention. An electrochromic device of the invention can be used, for example, as the component of reversibly variable transmittance in a variable-reflectance motor vehicle mirror. Among such mirrors provided by the invention are blue-tinted mirrors.

Highly stable, monochromatic and tunable optical radiation source and its application to high accuracy spectrophotometry

Abstract: An optical radiation source has been developed by coupling a dye laser to a small integrating sphere with an optical fiber. The radiant power from this source, which is monochromatic and spectrally tunable, has been stabilized to +/-0.02%. Nonuniformities in the emitted optical radiation field caused by speckle have been overcome by vibrating the fiber at ultrasonic frequencies. The source has been successfully used in a spectrophotometer to measure the transmittance of a large lens with an uncertainty of +/-0.01%, and the spectral responsivity of a filter radiometer with an uncertainty of +/-0.04%.

Soft x‐ray (97‐eV) phase retardation using transmission multilayers

Abstract: Phase retardation as a function of incidence angle of 97‐eV soft x rays from a laser plasma source on transmission through a free‐standing molybdenum/silicon multilayer was measured using a multilayer polarizer and a polarization analyzer. The maximum retardation of 49° between σ and π components is over 2/3 that calculated for an ideal structure. At maximum retardation the transmittance ratio of σ‐ to π‐amplitudes was 0.66 and the intensity transmittance, averaged for both components, was 20%. These multilayer structures will be useful in soft x‐ray polarization applications.

Method for producing color filter

Abstract: A method for producing a color filter involves (A) forming a photosensitive coating film on at least a transparent electrically conductive layer of a first substrate having both the transparent electrically conductive layer and a light-intercepting layer on its surface or a second substrate having the transparent electrically conductive layer on its outermost surface and a light-intercepting layer between the second substrate and the transparent electrically conductive layer and exposing the photosensitive coating film through a mask having patterns of at least three different degrees of light transmittances, and (B) developing and removing a photosensitive coating film region corresponding to a pattern having smallest degree of light transmittance or a pattern having largest degree of light transmittance for exposing the transparent electrically conductive layer and electrodepositing a colored coating on the exposed transparent electrically conductive layer for forming a colored layer thereon, operation of developing and removing the photosensitive coating film and electrodepositing the colored coating being sequentially repeated for the respective patterns having different degrees of light transmittances where the sequence of repetition is of increasing light transmittance or decreasing light transmittance.

Light scattering from a random rough interface with total internal reflection

Abstract: The scattering of linearly polarized electromagnetic waves incident from a dielectric from a rough surface separating the dielectric from a vacuum is studied by using the extinction theorem. The angular distributions of the ensemble average of intensity of the reflected and transmitted fields are calculated numerically for several values of the angle of incidence, the surface statistical parameters, and the dielectric permittivity. To determine the effect of the corrugation on the transmitted evanescent waves, we also obtain the angular spectrum of the transmitted field as a function of the momentum parallel to the surface in the nonradiative zone. The total mean reflected and transmitted energies (reflectance and transmittance), as well as their incoherent parts in the case of slight corrugations, are derived by integrating the angular intensity distribution over the angle of observation. This permits the analysis of the influence of the corrugation and of the phenomenon of total internal reflection within two different systems of surface correlation length T namely, for T larger and smaller than the wavelength. In particular, enhanced backscattering and forward transmission are predicted for surfaces with both T and the rms deviation greater σ than the wavelength of the incident light.

Shielding effectiveness of conductive polymers

Abstract: The plane wave shielding effectiveness of two new materials, conductive polymers polyacetylene and PBT doped by ion implantation with iodine, is evaluated as a function of frequency, electrical thickness, doping, polarization, and angle of incidence. Conductivity of the polymers, measured in previous investigations by the cavity perturbation technique, is used to compute the overall reflection and transmission coefficients of single and multiple layers of the polymers. The polymers are found to display excellent shielding effectiveness (better than 40 dB over a substantial frequency band). With recent advances in synthesizing stable highly conductive polymers these light-weight mechanically strong materials appear to be viable alternatives to metals for EMI shielding. >

Preparation and characteristics of new reverse mode film of polymer dispersed liquid crystal type

Abstract: A reverse mode operation has been achieved in a polymer dispersed liquid crystal (PDLC) film by a novel methodology. A mixture of a dual frequency addressable liquid crystal (crossover frequency (fc): 13 kHz at 298 K), an acryl monomer and an acryl oligomer was irradiated by UV light under the application of an electric field [50 V, 100 Hz(≪fc)] to give a reverse mode PDLC film. The film thus prepared shows 95% transmittance in the absence of an applied voltage (OFF state), while the transmittance decreases to 5% by applying 50 V at 50 kHz (≳fc) (ON state). Upon removal of the applied voltage, the film transmittance returns to 95%. The response time (the ON time: 24 ms and the OFF time: 74 ms) are similar to those of normal mode PDLC films.

Gabor zone plate with binary transmittance values.

Abstract: A methodology is presented for producing a Gabor zone plate by using a binary transmittance function that is both radially and azimuthally distributed on the surface of the plate. The measured optical properties of such a plate are shown to be in agreement with those of the idealized Gabor plate that possesses a radially sinusoidal transmittance function.

Optical Transitions in RF Sputtered CuInxGa1-xSe2 Thin Films

Abstract: Thin films of CuInxGa1-xSe2 were produced over the entire range of 0≤x≤1 by rf sputtering. The optical absorption coefficients of the CuInxGa1-xSe2 thin films were determined from the measured transmittance and reflectance in the wavelength range of 400 to 2000 nm. The optical absorption spectra for sputtered CuInxGa1-xSe2 thin films (x≠0) show three energy gaps, which are attributed to the fundamental edge, and band splitting by crystal-field and spin-orbit splitting, respectively. The primary transition energies exhibit bowing behavior expressed by the relationship Eg1=1.674-0.803x+0.130x2. The second and third transition energies are 0.06-0.08 eV and 0.22-0.27 eV above the primary transition energies, respectively.

Optical properties of Bi2Te2Se thin films

Abstract: Some optical parameters of Bi2Te2Se thin films, determined from the measured absorbance and transmittance at normal incidence in the visible spectral range, were studied as functions of film thickness and annealing temperature. These parameters were found to be sensitive to both film thickness and microstructure change caused by annealing in a film. The effect of thickness and temperature of annealing on the optical gap was interpreted in terms of elimination of defects and change of disordering in the amorphous matrix.

A simple instrument and technique for measuring columnar water vapor via near-IR differential solar transmission measurements

Abstract: A simple two-channel solar radiometer and data retrieval technique is described for sensing the columnar content of atmospheric water vapor via differential solar transmission measurements in and adjacent to the 940-nm water vapor absorption band. The instrument features two parallel channels for simultaneous measurements in and out of the absorption band to eliminate temporal variability effects in the differential comparison of the data from the two channels. The water vapor transmittance is determined by a modified Langley plot analysis of the ratio of the two channel signals. A statistical band model which closely follows the square-root law is then used to extract the columnar water vapor amount from the water vapor band transmittance. Error analyses and experimental results indicate that the instrument/technique can be reasonably employed to retrieve water vapor amounts with an error of 10% or less. >