Showing papers in "Journal of the Optical Society of America in 1959"

Infrared Spectra of Monolayers on Metal Mirrors

Abstract: A double-beam infrared spectrophotometer has been modified so that spectra of films as thin as one or a few monolayers in thickness on metal mirrors can be obtained. It is theoretically predicted and experimentally confirmed that, at the mirror surface, the electric intensity is predominantly perpendicular to the surface. Vibrational modes for which the matrix element of dipole moment is parallel to the surface appear abnormally weak in the spectra. The spectra, therefore, provide information about the orientation as well as the composition of sample films. Spectra of Blodgett films of metal stearates show differences in band positions and band intensities between films one molecular layer in thickness and thicker films. The shifts in band positions are attributed to interactions between carboxylate ions in films thicker than a molecular layer and the absence of such interactions in the first layer. The intensity differences are not explained.

Inference of Atmospheric Structure from Remote Radiation Measurements

Abstract: A detailed analysis of the structure of the atmosphere, including the three-dimensional distribution of temperature and water vapor, can be obtained from the spectral variation of its thermal radiation as viewed from a reconnaissance aircraft or earth satellite. In order that the measurements be capable of unambiguous interpretation, however, it is essential that the selection of spectral intervals to be used are based on a carefully planned interpretation scheme.A possible program is outlined, in which the temperature distribution is obtained by measurements in the 15-μ CO2 band and the water vapor distribution obtained by simultaneous measurements in the rotational band. The temperature-and-pressure dependence of the absorption coefficients must be taken into account.The instrument should be a multiple-slit or multiple-detector grating spectrometer, capable of resolving 10 cm−1 at 15 μ.Spectral models and methods of analysis of the spectra are discussed briefly.

Theory of the Concave Grating. I

Abstract: The theory of the concave grating has been examined in considerable detail by methods of geometrical optics. The results derived by means of geometrical optics were checked by comparing them with those based on physical optics in special cases. The conditions for image formation and aberrations in the image may be expressed by equations somewhat different from those given by Beutler which are shown to be in error. The astigmatism and other aberrations are treated with respect to finite length of slit illumination, finite grating size and deviations of the optical components from the Rowland plane but still lying on the Rowland cylinder. Within certain limitations, it is shown that the aberrations present in an off-plane Eagle mounting may be corrected by a very small rotation of the slit in a plane perpendicular to the optic axis. The optimum width of the grating, instrumental line half-width, and resolving power of the grating are also discussed. Finally, the Beutler treatment of the concave grating is examined in detail and the important errors are pointed out.

Two-dimensional motion of the retinal image during monocular fixation.

Abstract: A new modification of the contact lens technique was employed to record simultaneously vertical and horizontal components of eye movements. These were trigonometrically transformed to yield information about retinal image motion parallel to eight retinal meridia. It was found that eye movements occur predominantly in a small range of directions, which differs from subject to subject. Correlational and other statistical analyses of drift and saccadic movements led to the following conclusions about the nature of visual fixation: (1) Saccades compensate for the displacement of the retinal image away from some optical locus, but their probability of occurrence may increase with time since the last saccade, rather than with displacement. (2) The error signal to which saccades respond is probably generated 0.10 sec prior to their occurrence. (3) Parallel to those meridia where saccade compensation is poor, compensation by drifts becomes appreciable.

Spectral Emissivity of Tungsten

Abstract: An experiment designed to measure the spectral emissivity of tungsten, in which a direct comparison method is utilized so that the spectral emissivity is observed directly as the ratio of light intensity from a tungsten source to that from a blackbody source, is described. The spectral emissivity was measured over the wavelength interval 310 mμ to 800 mμ, and the temperature interval 1600°K to 2400°K.

Perceived Color and its Dependence on Focal, Surrounding, and Preceding Stimulus Variables*

Abstract: Alternative formal definitions of perceived color are examined. Both alternative formulations treat the responses evoked by stimulation of a focal test area, but in one case the influence of surrounding stimulation on the primary test area is taken into consideration, whereas this influence is ignored in the other formulation. The consequences of these alternative formulations for predictions of equivalent stimuli and for predictions of color appearance under different circumstances are discussed.Sensory scaling experiments are reported which yield direct quantitative estimates of the hue, saturation, and brightness attributes of perceived color, and of the dependence of these attributes on variations in focal, surrounding, and preceding stimulation. The relation of some of these dependencies to opponent neural induction mechanisms postulated by the opponent-colors theory is discussed.

Factors Influencing Accommodation Responses of the Human Eye

Abstract: Experiments are reported showing that a variety of clues such as chromatic aberration, spherical aberration, or astigmatism may be used to decide whether a monocularly viewed out-of-focus target requires an increase or decrease of accommodation for it to be refocused. When these clues are removed the initial direction of accommodation readjustment may be in error.

Reflecting Coatings for the Extreme Ultraviolet

Abstract: The conditions for preparing evaporated Al films of highest reflectance for mirrors and gratings to be used in the vacuum ultraviolet are summarized, and an account is given of aging studies. The preparation of bloom-free, one-micron thick coatings for grating blanks is described, and the effect of thin overcoatings on the efficiency of ruled gratings is discussed. Data are presented on the reflectance and aging of other film materials, such as Pt, ZnS, and Al2O3, which are more suitable for use at wavelengths below 1200 A. A discussion is given of the preparation and the reflecting properties of various multilayer film combinations suitable for reducing the reflectance of mirrors and gratings in the visible and the near ultraviolet while at the same time preserving a high reflectance in the extreme ultraviolet. A 250-A thick layer of MgF2 evaporated onto an Al coating immediately after its deposition was found both to raise the reflectance to about 80% at wavelengths down to 1200 A, and to retard aging.

Depth of focus of the human eye

Abstract: Depth of focus of the human eye is determined by the loss of resolving power (visual acuity) with increase in out-of-focus blurring of the retinal image. An instrument is described which permits accurate measurement of these phenomena, using psychophysical methods with the checkerboard visual-acuity test chart. All test conditions are held constant, binocular vision is maintained, and time of exposure of the test target is limited to 0.2 second. Depth of focus was measured under the two following conditions: (1) increase in the angular size of the test target, and (2) increase and decrease of pupil size as effected by suitable drugs. With the angular size of the test target equivalent to 20/25 Snellen notation, for three subjects the mean total depth of focus was found to be 0.94 diopter at the 50% level of probable visual resolution of the target details and 0.63 diopter at the estimated 99% level. It was found that for each step of increase in target size (20/25 to 20/30, and so on) the total depth of focus increased by about 0.35 diopter. It was found also that over the range of pupil size from 2.5 to 8.0 mm the total depth of focus decreased about 0.12 diopter per millimeter of increase in the size of the pupil. These results were reviewed with respect to hyperfocal distance.

Unit Magnification Optical System without Seidel Aberrations

Abstract: A unit magnification system is described which is free from Seidel aberrations and which can be used at very high aperture. The leading higher order aberrations are derived.A method using this system for reproducing photographically small groups of lines with a spacing of 6000 lines/in. is described.Several other possible applications of the system are outlined.

Analysis of eye movements during free search.

Abstract: The positive polarity of the human cornea was used to produce signals from marginal electrodes around the eyes The potentials were amplified with dc networks which produced amplitude-time oscillographic tracings of the horizontal and vertical components of eyeball movement, and also controlled the deflectors of a cathode-ray oscilloscope (CRO) in such a way that the beam moved in the same way as the eyes An automatic camera photographed the CRO face to produce two-dimensional electro-oculographic (EOG) plots of eyeball movement Data thus obtained are used for an analysis of eye movements and fixations in a surveillance search task The paper oscillographic tracings against time show (1) the number of fixations per unit of time, and (2) the duration of the fixations The cathode-ray EOG shows (1) the order of fixations in search procedure, (2) the lengths of various saccadic jumps, and (3) the areas of neglect and concentration for 5-sec search periods on a circular field subtending 30° of visual angle

High-speed infrared optometer.

Abstract: The various methods which have been used to detect changes in the refractive power of the eye due to accommodation are reviewed. An optometer of new design is described which uses infrared energy and therefore possesses the advantage of not acting as a glare source or as a stimulus to accommodation. The instrument has a noise equivalent to about 0.05 diopters when it is adjusted to detect fluctuations of accommodation from 0 to 5 cps. Normal fixation movements of the eye do not interfere with the measurements of refractive power. The optometer as described has been constructed from standard optical components which make it suitable for use in research, but it might readily be modified to suit particular users.

Performance Characteristics of a New Low-Temperature Bolometer

Abstract: An infrared bolometer detector designed to operate at liquid helium temperatures has been constructed by using the core of a carbon composition resistor as the sensitive element. We have made use of the well-known fact that the temperature coefficient of resistance of certain commercial carbon resistors is extremely large at low temperatures. Since the specific heat at these temperatures is small, it has proven to be relatively simple to construct a detector with a time constant of the order of milliseconds and a signal-to-noise figure surpassing any other known thermal detector of radiation. Furthermore the resistivity of the material is such that most of the radiation striking the surface is absorbed even at frequencies in the far infrared. A brief discussion of the noise to be expected under nonequilibrium conditions is given. In practice it is found that current noise is about an order of magnitude larger than all other sources of noise.

Photoionization Analysis by Mass Spectroscopy

Abstract: A vacuum ultraviolet monochromator has been combined with a mass spectrometer to study photoionization processes between 1570 and 430 A. Monochromatic photons were used to ionize, A, He, Ne, O2, N2, CO, NO, CO2, N2O, and NO2; and preliminary measurements of ion intensity as a function of photon energy have been obtained for the parent ions together with their fragments. The appearance of ionization and the structure of curves, in which ions per unit photon flux versus λ are plotted, will be related to previously reported energy levels, to photoionization cross sections, and to dissociative photoionization mechanisms.

Diffraction Images in the Polarizing Microscope

Abstract: In the polarizing microscope set for extinction, only that image whose polarization has been altered is available to form an image. The lenses themselves introduce such an alternation by rotation of the plane of polarization of rays having oblique incidence. This paper shows that the diffraction image of a pinhole has the form sin2θ·J3(r)/r, where θ and r are polar coordinates in the image plane. The image has four bright zones separated by a dark cross and the central pattern becomes a four-leaf clover form. The diffraction image of a point source through a plate of uniaxial crystal cut perpendicular to its optic axis (z-cut) is also a four-leaf clover when the polarizers are crossed. When the polarizers are parallel, the diffraction image becomes similar to that of an astigmatic system.

Effect of the size of a complex display upon visual search.

Abstract: This investigation is one of a series of studies designed to determine natural search tendencies during visual search tasks. In this study twelve subjects were presented an ordered series of experimental aerial maps of different size. Their eye traces were recorded on a modified ophthalmograph while they searched for a specific critical detail. As was noted in other experiments of this series, coverage of the display was not uniform. In particular, greatest attention was paid to the center of the display. Search behavior in displays subtending 9° and larger at the eye remained essentially the same. For smaller displays, marked differences were noted. As the size of the display decreased, durations of fixation increased, interfixation distances decreased, concentration of attention in the central area increased, and efficiency decreased. Efficiency is defined as percent of eye fixations falling within the display area. The implications of these findings are discussed.

Theory of the Concave Grating. III. Seya-Namioka Monochromator*†‡

Abstract: As an example of a mounting in which the optical components are not on the Rowland cylinder, the Seya-Namioka mounting is treated mainly from the standpoint of physical optics An ambiguity in the physical meaning of Beutler’s focal conditions is clarified; using the corrected condition a brief summary of the optical conditions in this mounting is given Astigmatism, spectral line shape, instrumental resolving power, and optimum grating width are discussed in detail and, for convenience of practical application, numerical results are also given for the following conditions: 1-m concave grating with 15 000 lines/in, first order spectrum, with ratios of the radius of curvature of the grating to the distances between the grating center and the entrance and exit slits 12223, and 12230, respectively, and the angle between the lines connecting the grating center to the entrance and exit slit 70° 15′

Optical Properties of Various Evaporated Rare Earth Oxides and Fluorides

Abstract: To furnish a greater choice of film materials for application in optical multilayer coatings, the optical properties of evaporated rare earth compounds such as Y2O3, La2O3, Pr6O11, Nd2O3, Sm2O3, Gd2O3, LaF3, NdF3, and CF3 were studied in the wavelength region from 0.22 micron to 2 microns. The materials were evaporated from tungsten boats and condensed on glass and fused quartz substrates at various temperatures. The optical constants n and k were determined mainly from reflectance, transmittance, and true thickness measurements. The following oxides were found to be useful because of their low absorption in the visible: La2O3 with n ranging from 1.85 to 1.95 with increasing thickness, Pr6O11 with n ranging from 1.92 to 2.05, also with increasing thickness, and Nd2O3 with n=2.05 for films of sufficiently low absorption. LaF3 (n=1.60) and NdF3 (n=1.61) showed no appreciable absorption in the whole wavelength region studied; CeF3 (n=1.63), however, exhibited two weak absorption bands at 0.234 and 0.248 microns. All n values are given at a wavelength of 0.5 micron and for unbaked films deposited at 300°C substrate temperature. The oxides condensed as almost amorphous films, whereas the fluorides developed fairly large grains as indicated by their sharp electron diffraction rings. All films were hard and showed excellent chemical and mechanical durability.

Optical and photoelectric properties of thin metallic films in the vacuum ultraviolet

Abstract: Measurements have been made on evaporated thin films of Al, Sn, In, Bi, Au, Ag, and Cd in order to correlate optical transmission, reflection, and photoemission in the far ultraviolet. Thin unbacked films prepared outside the spectrograph and glass-backed films prepared inside the spectrograph were used. The frequency at which the films change from a reflecting medium to a transmitting medium has been compared with the plasma frequency predicted by Bohm and Pines and also with electron energy eigenlosses in metals observed by Marton et al. Some new absorption transitions have been observed and related to x-ray absorption edges. A qualitative correlation between the photoelectric yields and corresponding optical properties has been attempted.

Study of the Experimental Factors Affecting Raman Band Intensities in Liquids

Abstract: The various instrumental factors which affect both peak and integrated Raman band intensities in liquids are discussed. These factors include the refractive index, color, and temperature of the sample; slit function and spectral sensitivity of the spectrophotometer; and the convergence and line width of the exciting radiation. Procedures for applying corrections for these factors relative to the 459 cm−1 band of carbon tetrachloride are presented. These considerations will allow good relative band areas to be obtained and will facilitate the interchangability of peak intensity data between different laboratories.

Visible and Ultraviolet Absorption Properties of Uranium Dioxide Films

Abstract: Films of uranium dioxide ranging in thickness from 132 to 280 mµ were evaporated onto fused silica, annealed at a pressure of 10−6 mm Hg and 960°C, and measured for optical absorption between the wavelengths of 210 and 800 mµ. A moderately intense band observed at 240 to 500 mµ has an unsymmetrical shape with a maximum at about 318 mµ, an approximately linear part with a moderate negative slope between 318 and 380 mµ, and a large negative slope between 380 and 500 mµ. This broad band is undoubtedly at least two unresolved peaks. From 240 mµ to shorter wavelengths there is a very intense absorption band which is most probably the fundamental band for UO2. The extinction coefficient was found to vary from 0.0055±0.0007 at 650 mµ to a maximum of 0.3702±0.0010 at 360 mµ and to a value of 0.167±0.004 at 240 mµ. The index of refraction varied from 2.29±0.03 at 800 mµ to a maximum of 2.58±0.22 at 450 mµ. The effect of oxidation of the films within the UO2 phase suggests that the one unresolved band at 430 mµ is removed by oxygen and the one at 300 mµ becomes more intense.

Properties of All-Dielectric Interference Filters. II. Filters in Parallel Beams of Light Incident Obliquely and in Convergent Beams

Abstract: The basic formulas derived in Part I are used to determine the wavelength of the transmission band when all-dielectric interference filters are used in parallel beams incident obliquely. Experimental results agree well with the theoretical predictions provided that the dispersion of the layers is taken into account.The transmission characteristics of filters in convergent beams are evaluated on the basis of the expressions for oblique incidence.

Achromatic Combinations of Half-Wave Plates

Abstract: The plane of polarization of two or more wavelengths can be rotated by a predetermined amount through the use of two or more identical half-wave plates in series, the axes of which are oriented at predetermined angles with respect to the incident plane of polarization. For two wavelengths a rotation of 90° may be accomplished by the use of two plates with their slow axes at angles of 22.5°+δ and 67.5°−δ, respectively. For three wavelengths a 90° rotation is obtained by using three plates at angles of 11.25°+δ, 45°, and 78.75°−δ respectively. The quantity δ is a small angle usually less than 1° which determines the spectral range of achromatization. Identical half-wave plates are easily obtained by cutting a single splitting of mica or a plane parallel sheet of other birefringent material. The wavelength for which the plates have half-wave retardation is not critical. Rather than having a smaller angular aperture than the single half-wave plate, the three-element achromatic rotator has a larger angular aperture. The use of the stereographic projection of the Poincare sphere for graphical solution of polarized light problems is discussed briefly.

Interferometric Spectroscopy in the Far Infrared.

Abstract: Michelson’s visibility technique for obtaining spectral distributions interferometrically in the visible region is compared with the new far-infrared interferogram method. The scanning function for the lamellar-grating type interferometric modulator that is used for the far-infrared region has been derived. Its theoretical resolution limit is compared with the spectrum estimate obtained from experimental results with a microwave source. Discrepancies between the derived spectrum estimate, obtained by a finite Fourier series expansion, and the true spectrum are discussed. A simple technique, due to Rayleigh, is invoked to avoid distortion of the spectrum due to the so-called Gibbs phenomenon. A spectrum of H2O extending from 8 to 60 cm−1 (λ = 1250 to 167 μ) illustrates the application of Rayleigh’s method.

Neural limitations of visual excitability. I. The time course of monocular light adaptation.

Abstract: Monocular visual excitability was studied psychophysically by determining the threshold intensity for a small (40-min) brief (5-msec) “test” flash centered within a larger (3°) “conditioning” flash, both presented at 7° of arc in the temporal half-field. Interval between flashes was varied from −200 (test flash preceding onset of conditioning) to +1500 msec (test flash following), nine combinations of conditioning flash intensity and duration being used as parameters. For all combinations, threshold rose between −200 and −100 msec (before the start of the conditioning flash), reaching a maximum increment when the onsets of the two flashes were synchronized. When test was superimposed upon conditioning flash in time (positive intervals), threshold declined to approach an asymptote near the end of the latter flash. Following termination of the conditioning flash, threshold returned to resting level. The maximum rise in threshold, as well as the time taken to achieve an asymptote, varied with both intensity and duration of the conditioning flash. When a rough estimate of the photochemical contribution to these threshold changes was subtracted from the raw data, residual threshold increments were obtained and attributed to neural processes. On the basis of time course, it is suggested that these neural processes involve central (geniculocalcarine) as well as peripheral (neuro-retinal) factors.

Fluorescence and gray content of surface colors

Abstract: An investigation of the colors in the Munsell 5R plane and an extension of this study to colors produced in a small aperture in a large white illuminated surround have led to the discovery of some interesting and novel relationships. It is found that under these conditions the domain of surface color perception includes the whole of the range from V = 0 to 10 and pc = 0 to 1.0 and under some conditions more. For a color of a given dominant wavelength there is a locus lying wholly within this space along which lie colors that do not appear to contain gray. If luminance or purity is increased above a point on this line, the sample takes on the appearance characteristic of a fluorescent material. If either is decreased below a point on this line, the color is perceived as having a gray component added to the purely chromatic component in increasing amounts until at pc = 0, there is no chromatic component perception of the color or at low values of V the sample appears black. Above a point somewhat higher than surround luminance, the appearance of fluorescence ceases and the surface mode changes to the illuminant mode, the saturation of the perceived color decreasing with increasing luminance above this point. An hypothesis is suggested to explain the facts and it is pointed out that more than one kind of “brightness” is necessarily involved.

Quantum Efficiency of Human Vision

Abstract: The detective quantum efficiency for foveal vision is computed from the flash perception data of Blackwell and McCready. The detective quantum efficiency is identical with the concept of quantum efficiency introduced by Rose in 1946, and is defined as the square of the ratio of the smallest possible threshold to the observed threshold, where the smallest possible threshold is set by the statistical fluctuations in the number of the background photons entering the eye. The computed values of the detective quantum efficiency Q are tabulated in Table V, and depend on the target diameter α, on the light pulse duration T, and on the background luminance B. The maximum values of Q (with the respect to variation of α and T) range from about 0.25% to about 1.0 %over the range from 0.1 to 100 ft-L, with the maximum value occurring at about 1.0 ft-L. The computed values of Q are free of the questionable assumptions previously used by Rose and by Jones regarding integration time and threshold signal-to-noise ratio.

On the Propagation of Mutual Coherence

Abstract: Section 1 presents a brief history of the development of coherence theory and discusses some of the advantages of Wolf’s general formulation of the theory in terms of Gabor’s analytic signalsSection 2 contains an analysis of the limiting cases of coherence and incoherence, showing for these extremes the form of the mutual coherence function in a quasi-monochromatic field In particular it is shown that in such a field coherence is characterized by a mutual coherence function which, apart from a simple periodic factor, is expressible as the product of a wave function with its complex conjugate, each factor depending on the coordinates of one point only It is also shown that an incoherent field cannot exist in free spaceThe mutual coherence function obeys rigorously two wave equations, and in Sec 3 these equations are solved with the help of appropriate Green’s functions to find the field produced by a general plane polychromatic source The solution is simplified by the quasi-monochromatic approximation; and the limiting cases are discussed in detail showing that a coherent source always gives rise to a coherent field, and that a well known theorem of Van Cittert and Zernike represents an approximation to the incoherent limit of the quasi-monochromatic solution

Solar Spectral Irradiance and Vertical Atmospheric Attenuation in the Visible and Ultraviolet

Abstract: The solar spectral irradiance outside the earth’s atmosphere was determined by Langley’s method of extrapolation to zero air mass, from measurements taken on Mount Lemmon at an elevation of 8025 ft near Tucson, Arizona, during October, 1951. The spectrum was produced and the energy scanned by a Leiss quartz double-monochromator, detected by a 1P21 photomultiplier, amplified, and presented on a strip chart recorder. About twenty-five spectra were recorded from sunrise to noon, with band widths ranging from 10 A at 3030 A to 170 A at 7000 A. The equipment was calibrated frequently by recording the spectrum of a standard tungsten lamp. Compared with earlier work performed in this field, our results agree best with those of Pettit. There is good agreement with the direct measurements from a rocket obtained by Purcell and Tousey in 1954 and with the Sacramento Peak ultraviolet observations by Stair and Johnston in 1955. The change of solar intensity with air mass showed that the attenuation of the atmosphere above Mount Lemmon was approximately 15% higher than that for a Rayleigh atmosphere in the region 3400 A to 4650 A, where there is no absorption due to ozone. A discussion is included which emphasizes the importance of clear and constant atmospheres which are necessary to obtain accurate values of solar spectral irradiance outside the earth’s atmosphere by the Langley method. The solar illuminance computed from spectral data was 12 700 lumens/ft2.