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Reflectances of transmissive sheets, calculated from the transmissions of one and two sheets, are compared with reflectances obtained by using the General Electric recording spectrophotometer. The expression used as a basis for calculation, Ra=(1−Ta2/T2a)12, in which Ra is the reflectance, and Ta and T2a are the transmissions of one and two sheets, respectively, of a, was derived by considering the infinite series of reflections undergone by light, or radiant energy in general, in passing through the two sheets. The expression was found to be valid and useful over a wide range of reflectances and wave-lengths, for materials such as paper, glass, and an organic plastic.The method is an absolute one since it involves no reflectance standard. It involves no spherical or similar integrating device nor does it involve any reflecting surface other than that of the sample itself, as a fundamental part of the measurements. When transmission values for diffuse incidence are substituted into the expression, the reflectances thus calculated correspond to the conditions of diffuse incidence and diffuse viewing, and as such are somewhat higher than the usual directly measured reflectances for normal incidence and diffuse viewing (or diffuse incidence and normal viewing). For clear sheets, with normal incidence, specular reflectance may be calculated.The method thus affords a means of determining, from two simple measurements, the specular-plus-diffuse reflectance of transmissive sheets for diffused light or radiant energy in general.The expression as derived is theoretically inapplicable to diffusing sheets for light of normal incidence, but a compensation of errors allows close agreement over the visible range, at 365 millimicrons, and for “white” light, for all except tissue paper and other materials of like transmissivity. For diffuse incidence at 365, and to a certain extent, at 405 millimicrons, some papers show deviations from the simple theory because of fluorescence effects. This and other effects are discussed.Reflectances in the infra-red region near 850 millimicrons are also calculated but no standard for comparison is available for these values. The sources of errors at the shorter wave-lengths, however, do not interfere in the infra-red region.Transmissions of papers were found to be dependent upon the angle of incidence.Reflectances throughout the visible region, measured at 45° from normal incidence were found to agree closely, for the type of papers studied, with those obtained using the General Electric recording spectrophotometer, which corresponds to the conditions of normal incidence and diffuse viewing.

This bibliography is a collection of papers dealing primarily with the far infrared spectral region between 25 and 1000 μ. It is arranged in chronological order, the articles being alphabetized in each year by first author’s last name. The information is given in the order author, title of paper, and reference.

The term, photoelectric colorimetry, is commonly employed to designate both photoelectric tristimulus colorimetry, used to evaluate the appearance of materials, and abridged spectrophotometry, often used to assist in chemical analyses. This paper is devoted to the first type of measurement. For a photoelectric tristimulus colorimeter, it is desired to find three or more source-filter photo-cell combinations of such spectral character that they duplicate the standard I.C.I. observer for colorimetry. With an instrument having these combinations, tristimulus values would be obtained by direct measurement. Although no one has duplicated the I.C.I. observer perfectly, several investigators have obtained source-filter photo-cell combinations suitable for the measurement of color differences between spectrally similar samples. To measure color differences as small as those which the trained inspectors of paint, textile, plastic, paper, and ceramic products can see, an instrument must have high precision. If the needed precision is available, a photoelectric tristimulus colorimeter may be used to measure: (1) I.C.I. colorimetric values, x, y, and Y, relative to those of a spectrally similar, calibrated standard; (2) relative values of α and β, components of the chromaticity departure from neutral in a new uniform-chromaticness-scale mixture diagram for representing surface colors; (3) amounts of color difference between pairs of spectrally similar samples; (4) amounts of color change accompanying fading; and (5) whiteness of white and near-white surfaces. In giving examples of the measurement of some of these different properties and in describing the errors of color measurement to which the tristimulus method is subject, reference is made to operations with the author’s recently developed multipurpose photoelectric reflectometer.

The results of a preceding paper [ J. Opt. Soc. Am.65, 1464, ( 1975)] are viewed from a different angle as providing the basis for the design of film–substrate single-reflection linear partial polarizers (LPP), which also operate as reflection optical rotators. The important characteristics of a comprehensive set of discrete designs of SiO2-Si LPP’s at λ = 6328 A are shown graphically.

Though heterodyne detection provides a valuable technique for detecting small signals, the conventional system has several inherent disadvantages. In applications such as communications and radar, obtaining a reasonably high signal-to-noise ratio (SNR) requires (1) a good knowledge of the velocity of the transmitter or target, (2) a stable yet tunable local oscillator, and (3) a target or source that presents a minimum of frequency broadening. These conditions are frequently not adhered to by real systems, particularly in the ir and optical, giving rise to detection capabilities far below optimum. Calculations are presented for the use and operation of a three-frequency nonlinear heterodyne system that eliminates many of the stringent conditions required for conventional heterodyne detection, while maintaining its near-ideal SNR. The technique, which is similar in principle to heterodyne radiometry, makes use of a two-frequency transmitter and a nonlinear second detector and is particularly useful for signal acquisition; for signals of unknown Doppler shift, in fact, performance is generally superior to that of the conventional system. Although primary emphasis is on the ir and optical because of the large Doppler shifts encountered there, application of the principle in the microwave and radiowave is also discussed. For cw radar and analog communications, the SNR, power spectral density (PSD), and minimum detectable power (MDP) are obtained and compared with the standard configuration. Both sinewave and Gaussian input signals are treated. A variety of specific cases are discussed including the optimum performance case, the typical radar case, and the AM and FM communications case. Evaluation of the technique for pulsed radar and digital communications applications (both in the absence and in the presence of the lognormal atmospheric channel) is reserved for Part 2 of this paper [Appl. Opt. 14, 680 (1975)].

A scheme of combined reflection and transmission ellipsometry on light-transmitting ambient-film-substrate systems is proposed and the required sample design and instrument operation are investigated. A comparative study of the sensitivity of external and internal reflection and transmission ellipsometry is carried out based on unified linear approximations of the exact equations. These approximations are general in that an arbitrary initial film thickness is assumed. They are simple, because a complex sensitivity function is introduced whose real and imaginary projections determine the psi (Psi) and delta (Delta) sensitivity factors. Among the conclusions of this paper are the following. (1) External reflection ellipsometry near the Brewster angle of a transparent ambient-substrate system is extremely sensitive to the presence of very thin interfacial films. For example, films as thin as 10(-5) A of gold are readily detectable on glass substrates at an angle of incidence 0.3 degrees below the Brewster angle, assuming a measuring wavelength of 5461 A with an ellipsometer of 0.05 degrees precision. (2) The formation of thin nonabsorbing films at the interface between transparent ambient and substrate media is not detectable, to first order, as a change in the ellipsometric angle Psi by either internal or external reflection or transmission ellipsometry. (3) The film-detection sensitivity of transmission ellipsometry increases monotonically with angle of incidence. (4) For each angle of external incidence there is a corresponding angle of internal incidence that leads to the same values of the reflection and transmission sensitivity functions. These angles are interrelated by Snell's law. (5) The ranges of validity of the linear approximation in reflection and transmission ellipsometry are comparable. The case of total internal reflection ellipsometry may lead to strong nonlinear behavior of Psi and Delta as functions of the film thickness in the range below 0.05 of the wavelength of light.

Surface appearance, apart from texture, is defined by the goniophotometric curve giving the angular distribution of the reflected light. A summary of current goniophotometric techniques shows that essential parts of these fundamental data have been neglected. This paper applies an established method of statistics to the problem of goniophotometric-curve analysis and interpretation whereby such data are reduced to dispersion, skewness, and kurtosis indexes. The kurtosis index is shown to correlate better with subjective estimates of the distinctness of the reflected images than the conventional measure, 60° specular gloss. The kurtosis index is applied to one problem in the selection of optimum glossmeter geometry.

The Michelson interferometer, IRIS-D, flown on Nimbus 4 in April 1970 is an improved version of the interferometer, IRIS-B, flown on Nimbus 3 a year earlier. Thermal emission spectra of the earth are being recorded between 400 cm(-1) and 1600 cm(-1) with a nominal spectral resolution of 2.8 cm(-1) and a noise equivalent radiance between approximately 0.5 and 1 erg sec(-1) cm(-2) ster(-1) cm. This paper describes the design and performance of the IRIS-D and concentrates on the design differences that exist between the interferometers flown on Nimbus 3 and 4. The performance is demonstrated by examples of spectra obtained while in earth orbit.

The multipurpose reflectometer was developed primarily to measure apparent reflectance, specular gloss and trichromatic coefficients. These measurements are useful in the ceramic, paint, textile, paper and chemical industries to indicate lightness, gloss and color of finished articles. In the reflectometer, two light beams from a single source are directed along separate paths to two barrier-layer photo-cells. Various types of these photo-cells were studied to find which could be used most advantageously. The reflectometer employs a substitution null method and requires a galvanometer to indicate equality of the currents generated by the two photo-cells. For each sample tested, there is a photometric adjustment to restore equality of the currents. The amounts of photometric adjustment are measured on the direct-reading scales; one of which is used for apparent reflectance and the other for specular gloss. Because of its high precision, the instrument is well suited for measuring small differences in apparent reflectance, gloss or color of nearly identical samples. However, for greatest accuracy, it is necessary to correct the scale readings by calibration.

A tristimulus photoelectric colorimeter has been designed to measure the chromaticities of pyrotechnic smokes having highly saturated colors. To obtain a compact housing for three multiplier phototubes, “head-on” type (RCA 5819) phototubes are used. For high sensitivity and stability the photometric units are three Photovolt Multiplier Photometers, Model 520-M. To minimize edge effects and rear wall reflection, the smoke chamber was designed as a 36-inch cube. The chamber is illuminated by four 150-watt flood lamps placed to yield uniform illumination on the viewing window. Three filters were designed to approximate the daylight CIE standard observer functions for the source-filter-phototube combinations of the instrument. As the CIE y¯ and z¯ functions are unimodal, little difficulty was encountered in designing the filters to approximate these functions. The CIE x¯ function, which is bimodal, required a divided filter to approximate its two lobes. The filter constructed was composed of two sectors, one approximating the “blue lobe,” the other approximating the “red lobe,” of the x¯ function. Satisfactory results have been obtained with this colorimeter using Munsell papers as standards.

This paper defines the time-invariant detection scheme which yields the largest average signal-to-noise ratio in the heterodyne detection of a randomly distorted optical signal. It is shown that the detection scheme may be realized by properly shaping both the isophase surface and the irradiance distribution of the local-oscillator beam. Applied to the case of an atmospherically distorted optical plane wave it is shown that although the optimum local-oscillator beam differs significantly from a plane wave, the increase of average signal-to-noise ratio, over the plane-wave case as reported by Fried, is negligible (less than 10%).

In the last ten years a great deal of work has been done on the experimental investigation of atomic energy levels using magnetic resonance techniques. This paper concerns itself primarily with a review of some of the studies of atomic vapors in connection with level structures, on the one hand, and the mutual interactions of light oscillating magnetic fields and the effects of collisions, on the other.

In 1934, Gibson, Walker, and Brown developed sets of four colored glass filters to serve as working standards of spectral transmittance for checking the reliability of spectrophotometers. Several sets of these glasses were measured carefully and reserved and designated as future reference standards. Duplicate standards evaluated by comparison with the reference standards are available by purchase to the public. The current set of reference standards was established in the years 1945 to 1947, and one of these reference standards (selenium-red) was recalibrated in 1952. This paper reports a recalibration, made in 1961 and 1962, of all four glasses (selenium-red, carbon-yellow, copper-green, cobalt-blue) on three spectrophotometers (Cary 14, Beckman DU, Konig-Martens). Except for the cobalt-blue standard, the values of spectral transmittance found differ from those previously assigned by amounts differing at some wavelengths by as much as or slightly more than the uncertainties estimated for the present values, though not by amounts exceeding the combined uncertainties of the present and previous determinations. The indicated changes for these three standards are fairly regular, however, and support the view that the selenium-red and carbon-yellow standards are changing chiefly by formation of a reflectance-reducing film on the surfaces. The indicated rate of upward drift is slow, and suggests that it takes about 10 years for the drift to exceed the assigned uncertainity.

Recent work by Jacobsen in the colorimetry of titanium pigments has indicated that the ICI standard observer weights too lightly the spectral region below 430 mμ to accord with visual perception by average observers. This paper presents a repetition of this work for a single pair of titanium-pigment paints whose difference was measured by spectrophotometric means and then by seven observers by means of a visual colorimeter. Four of the seven observers corroborated Jacobsen’s conclusion; three checked closely the standard observer. A modified standard observer based upon the spectral luminosity determinations of Gibson and Tyndall and Wald has been derived and is shown to account closely for the settings of the group of four observers that disagreed with the standard observer.

This paper reviews the problem of absolute photometric calibration in the extreme uv range with particular reference to a solar satellite instrument. EUV transfer standards, the use of predispersing spectrometers, and polarization effects at near normal incidence are discussed. Changes in preflight calibration associated with the general problems of contamination are given as the background to the main discussion relating to changes in photometric calibration during orbital operation. Conclusions relating to adequate photometric measurements in orbit are drawn, with a short list of the "best" solar flux measurements for reference. Finally, the importance of rocket flights for photometric calibration of satellite instruments is indicated.