Showing papers in "Applied Optics in 1965"
TL;DR: The spectral properties of plant leaves and stems have been obtained for ultraviolet, visible, and infrared frequencies as discussed by the authors, including reflectance, transmittance, and absorptance for certain plants.
Abstract: The spectral properties of plant leaves and stems have been obtained for ultraviolet, visible, and infrared frequencies. The spectral reflectance, transmittance, and absorptance for certain plants is given. The mechanism by which radiant energy interacts with a leaf is discussed, including the presence of plant pigments. Examples are given concerning the amount of absorbed solar radiation for clear sky and overcast conditions. The spectral properties of desert plants are compared with those of more mesic plants. The evolution of the spectral properties of plant leaves during the early growing season is given as well as the colorimetric behavior during the autumn.
1,300 citations
TL;DR: In this paper, a new theory of Wood's anomalies is presented which is based on a guided wave approach rather than the customary multiple scattering procedure, which provides both new insight and a method of calculation.
Abstract: A new theory of Wood’s anomalies is presented which is based on a guided wave approach rather than the customary multiple scattering procedure. This approach provides both new insight and a method of calculation. It is shown that two distinct types of anomalies may exist: a Rayleigh wavelength type due to the emergence of a new spectal order at grazing angle, and a resonance type which is related to the guided complex waves supportable by the grating. A general theoretical treatment is presented which makes use of a surface reactance to take into account the standing waves in the grating grooves, and which derives the locations and detailed shapes of the anomalies. Rigorous results are obtained for a specific example; the amplitudes of all of the spectral orders are determined explicitly, and the Wood’s anomaly effects are demonstrated clearly in graphical form for a variety of cases.
1,099 citations
TL;DR: In this article, the authors present concepts, terminology, and symbols for specifying and relating directional variations in reflectance and emissivity of an opaque surface element. But their relationship to more familiar concepts, including those of perfectly diffuse and specular reflectance, is not discussed.
Abstract: Concepts, terminology, and symbols are presented for specifying and relating directional variations in reflectance and emissivity of an opaque surface element. Their relationship to more familiar concepts, including those of perfectly diffuse and specular reflectance, is given, and they are applied to illustrative examples. It is shown that, when the usual reciprocity relationship holds, the reflectance for a ray incident on an opaque surface element is related by Kirchhoff's law to the emissivity of that element for a ray emitted along the same line in the opposite sense.
734 citations
TL;DR: In this paper, a long optical path has been folded between two 7.5 cm diam spherical or aspherical mirrors to provide an output beam which can be well separated from previous reflections with 1000 or more passes between the mirrors.
Abstract: A long optical path has been folded between two 7.5-cm diam spherical or aspherical mirrors to provide an output beam which can be well separated from previous reflections with 1000 or more passes between the mirrors. The 3000-m path provides 10 μsec of delay. This system can be used as a dispersionless optical delay line for use in filtering or storage of information modulated onto the light beam. The pattern of beams between the two mirrors is obtained in one of two ways. A small perturbing mirror may be inserted to give a series of offset ellipses, or one or both of the mirrors can be made astigmatic to give a Lissajous pattern of spots on each mirror. The output beam can be separated from others by discriminating in both angle and position. The diffraction losses of the system are much lower than those for an open beam because of the periodic focusing of the spherical mirrors. The extreme dependence of the loss of the delay line upon the absorption and scattering loss of the mirrors makes the system dependent upon very low loss mirrors and also makes the system a suitable method for measuring mirror loss. Block diagrams are shown for some possible filtering and storage applications.
542 citations
TL;DR: In this article, a theoretical analysis of Gaussian beam propagation in media where the refractive index and/or the gain constant varies quadratically with the distance from the optic axis is made.
Abstract: A theoretical analysis is made of Gaussian beam propagation in media where the refractive index and/or the gain constant varies quadratically with the distance from the optic axis. Use of a complex beam parameter simplifies the analysis. A differential equation for the complex beam parameter is deduced from the wave equation for the complex beam parameter is deduced from the wave equation, and various of its solutions are discussed. This includes a discussion of light propagation in media with a gain profile, which are found capable of supporting stationary beams of constant diameter.
510 citations
275 citations
215 citations
TL;DR: In this article, the authors proposed two plano-aspheric lenses and a pair of selectively aberrated lens systems for converting the plane wave from a laser in the uniphase TEM0,0 mode to a plane wave having uniform irradiance over a required cross section, and all the power of the original beam.
Abstract: Interest has recently been shown in methods of converting the plane wave from a laser in the uniphase TEM0,0 mode to a plane wave having (a) uniform irradiance over a required cross section, and (b) all the power of the original beam. Two methods are proposed for accomplishing these aims: one employs two plano-aspheric lenses; the other requires a pair of selectively aberrated lens systems. A computer program has been written which determines the aspherics, and one example is presented. The aberrations required of the second method are expressed algebraically in terms of known quantities. These aberrations could conceivably be designed into a system of spherical lenses, by use of one of the automatic lens design programs now extant.
161 citations
TL;DR: In this article, the reflectance of silver and gold was measured in the wavelength range from 0.5 μ to 32 μ, and it was found that the reflectances of both materials are higher than previously-reported values, and that ultrahigh vacuum silver films have the highest infrared reflectance over an extended wavelength range of any known material.
Abstract: The reflectance of silver and gold evaporated in ultrahigh vacuum, has been measured in the wavelength range from 0.5 μ to 32 μ. It was found that the reflectance of both materials is higher than previously-reported values, and that ultrahigh vacuum silver films have the highest infrared reflectance over an extended wavelength range of any known material. The infrared emittance of uhv gold films is nearly as low as that of silver and is smaller by nearly a factor of 3 than the value previously reported for this material. Since gold is chemically inert and its emittance apparently does not change with time, it should find wider application as a low infrared emittance material, particularly in problems involving radiative heat transfer.
154 citations
IBM1
124 citations
TL;DR: The majority of the laser lines observed are shown by comparison with calculated relative line strengths to be the strong lines predicted by L-S coupling that possess lower levels optically connected to the ion ground state as discussed by the authors.
Abstract: Laser oscillation has been observed at one hundred and eighteen wavelengths in ionized neon, argon, krypton, xenon, oxygen, and other gases in the spectral range 2677 A to 7993 A. Of these lines, ninety-six have been definitely identified, and arise from singly, doubly, and triply ionized atoms. A 2-m, pulsed dc discharge was employed. Measured and calculated wavelengths and level classifications are tabulated. The majority of the laser lines observed are shown by comparison with calculated relative line strengths to be the strong lines predicted by L-S coupling that possess lower levels optically connected to the ion ground state. The rules ΔS = 0, ΔJ = ΔL = +1 are reasonably well obeyed, although violations of L-S restrictions on core change and multiplicity are also observed. Evidence of upper level population by electron collision with ground-state ions is presented. The time dependence of laser output under pulsed excitation is discussed.
TL;DR: In this article, the authors present some of the background required to understand the phenomenon of emission polarization, which is not as well-known as it should be, and the explanation that the phenomenon involves refraction of all emitted radiation, advanced by Millikan in 1895, is still accepted today.
Abstract: Certain experiments had indicated that the polarization of emitted radiation was much more prevalent than had been expected. This paper is intended to present some of the background required to understand the phenomenon of emission polarization, which is not as well-known as it should be. The explanation that the phenomenon involves refraction of all the emitted radiation, advanced by Millikan in 1895, is still accepted today. More recent work, substantiating Millikan’s explanation, is cited.
TL;DR: In this article, a computer program for the completely automatic design of optical thin film systems by evolution which does not require a starting design is described. But this program does not address the problem of choosing a suitable starting design for refinement.
Abstract: The various methods for the synthesis of optical thin film systems with prescribed properties are reviewed. One general approach is to refine numerically the properties of an initial system. In many problems, however, the choice of a suitable starting design for refinement is not at all obvious. The present paper describes a computer program for the completely automatic design of optical thin film systems by evolution which does not require a starting design. Apart from the specification of the desired optical properties of the system, the only input data necessary are the refractive indexes of the substrate, the medium, and the thin film materials that may be employed for the construction of the coating. Optical properties that may be specified at present include transmittance, reflectance, phase changes on transmission and reflection, and the first and second derivatives of these quantities, with respect to wavenumber and angle of incidence. Several examples are given to illustrate the performance of this program. Ways are indicated in which this automatic design program can be improved further in the future.
TL;DR: In this article, a technique for producing a matched filter, wherein the filter transfer function is modulated onto a spatial carrier and the resulting function is hard-clipped allowing a filter construction of completely opaque and transparent lines, is given.
Abstract: Matched filtering is described as a spatial filtering operation. A technique for producing a matched filter, wherein the filter transfer function is modulated onto a spatial carrier and the resulting function is hard-clipped allowing a filter construction of completely opaque and transparent lines, is given. The effect of this nonlinearity on the S/N is shown to be small. The effects of extraneous frequencies in the filter is shown to be negligible if the spatial carrier is sufficiently high. Experimental results are presented showing the detectability of the signal in the presence of various levels of additive noise.
TL;DR: The method of wavefront reconstruction can be used in three ways to extend the usefulness of interferometry, and will be particularly useful for investigating transient phenomena, such as are encountered in wind-tunnel or shock-tube testing.
Abstract: The method of wavefront reconstruction can be used in three ways to extend the usefulness of interferometry. First, a multiple fringe interferogram with a different fringe spacing, and/or a zero-order interferogram can be produced from a multiple fringe interferogram. Second, a multiple fringe interferogram can be used to produce a new interferogram which is focused on a particular plane of the object field. Third, a schlieren photograph and/or shadowgraph can be produced from an interferogram. The technique will be particularly useful for investigating transient phenomena, such as are encountered in wind-tunnel or shock-tube testing. The limitations of the technique are reviewed.
TL;DR: In this article, the nature of photoconductive effects at wavelengths longer than 100 μ is discussed with particular reference to n-type InSb in zero magnetic field, magnetic fields too low to produce magneto-optical resonance absorption, and large magnetic fields.
Abstract: The nature of photoconductive effects at wavelengths longer than 100 μ is discussed with particular reference to n-type InSb in (a) zero magnetic field, (b) magnetic fields too low to produce magneto-optical resonance absorption, and (c) large magnetic fields. The performance of practical detectors using these effects is described and is compared with that of other submillimeter detectors.
TL;DR: A review of recent developments in the gas laser field is given which is intended to supplement a previous, more detailed paper by the author on the same subject as discussed by the authors, and a number of new results have been described.
Abstract: A review of recent developments in the gas laser field is given which is intended to supplement a previous, more detailed paper by the author on the same subject. In addition, a number of new results have been described. The present paper has six main sections dealing with: a summary of general laser considerations, inversion saturation mechanisms in four-level systems, possible two- and three-level collision lasers, stimulated emission pumping, transient inversions, and ion lasers. Emphasis has been placed on atomic systems in this work and a summary of currently known gas laser transitions is included as an appendix to this paper.
TL;DR: In this article, the vacuum ultraviolet continua of the rare gases helium (580-1100 A), argon (1050-1550 A), krypton (1250-1800 A), and xenon (1480-2000 A) have been excited in a condensed discharge using a recently developed thyratron modulator excitation unit which gives sufficient intensity for photoelectric scanning at a bandwidth of 0.25 A.
Abstract: The vacuum ultraviolet continua of the rare gases helium (580–1100 A), argon (1050–1550 A), krypton (1250–1800 A), and xenon (1480–2000 A) have been excited in a condensed discharge using a recently developed thyratron modulator excitation unit which gives sufficient intensity for photoelectric scanning at a bandwidth of 0.25 A. The optimum conditions for excitation have been studied. The continua excited in this manner have been compared with microwave-excited continua and found to be significantly more intense for argon and about the same intensity for krypton and xenon. It was not possible to obtain the helium continuum using microwave excitation. Time-resolved measurements of the light emission, current, and voltage made for these continua show that the light emission may begin either before or after the current pulse.
IBM1
TL;DR: Theta modulation as mentioned in this paper allows the production of a color image from a black and white film, on which the color object is recorded in encoded form, and nonlinear characteristics (H & D curves) of any shape can be realized.
Abstract: The experiments reported in this paper are similar to the famous Abbe experiments. However, they were done for quite different reasons, namely, to perform certain information processing operations by optical means. Our technique, called theta modulation, allows production of a color image from a black and white film, on which the color object is recorded in encoded form. Furthermore, nonlinear characteristics (H & D curves) of any shape can be realized. A special application of theta modulation, called multiplex storage, will be described. By this technique, more than one image can be recorded in the same area on a piece of film. Subsequently, the individual images can be recovered with a minimum of crosstalk.
TL;DR: Collimator with wide fields of view detectors designed for extraterrestrial X-ray source measurements as discussed by the authors was used for the first time in the early 1990s. But it was not used for any extraterrestrial applications.
Abstract: Collimator with wide fields of view detectors designed for extraterrestrial X-ray source measurements
TL;DR: In this paper, the transmittance characteristics in the extreme ultraviolet of unbacked films are discussed; data are presented for films of Al, In, Bi, Ge, Si, and certain organic materials.
Abstract: The transmittance characteristics in the extreme ultraviolet of unbacked films are discussed; data are presented for films of Al, In, Bi, Ge, Si, and certain organic materials. Generally, the metals begin to transmit shortward of their critical wavelengths, determined by the electron eigenloss, and reach maximum transparency at the nearest x-ray edge; to shorter wavelengths regions of transparency exist between the other x-ray edges. Their use in order-sorting, and for eliminating long-wavelength stray light, is illustrated with laboratory spectra and solar spectra obtained from rockets.
TL;DR: In this paper, a simple experimental method for determining the degree of plane polarization of a far ultraviolet monochromator was developed and tested, which requires only a measurement of the reflectance at 45° angle of incidence with two or more orientations of a reflector about the optic axis.
Abstract: A simple experimental method for determining the degree of plane polarization of a far ultraviolet monochromator was developed and tested. This determination requires only a measurement of the reflectance at 45° angle of incidence with two or more orientations of the reflector about the optic axis. This procedure works at all wavelengths without requiring a detailed knowledge of the optical constants of the reflector material. The degree of plane polarization has been determined for a 0.5-m Seya-Namioka monochromator. The polarization has been found to depend strongly on wavelength and on both the grating and the grating overcoating.
TL;DR: A detailed review of methods for the measurement of radiative decay rates and total inelastic destructive cross sections of short-lived excited states is given in this paper, where the main emphasis is given to experimental techniques devised by the authors for measurement of excited state lifetimes in the 4-nsec to 1000-Nsec range and analysis of data taken in the noble gases with this system.
Abstract: A detailed review is given of methods for the measurement of radiative decay rates and total inelastic destructive cross sections of short-lived excited states. The paper is divided into six main sections, dealing with methods of approximate calculation and interpretation of radiative and collision processes; previous methods of measurement; a review of delayed multichannel coincidence techniques; properties of the vernier chronotron; methods of statistical analysis; and a summary and analysis of data pertinent to laser transitions in helium, neon, and singly ionized argon. The main emphasis is given to experimental techniques devised by the authors for the measurement of excited state lifetimes in the 4-nsec to 1000-nsec range and the analysis of data taken in the noble gases with this system.
TL;DR: In this paper, the Mie theory angular scattering distributions for spherical particles of refractive index m = 1.2 (0.2) to 2.4 (1.4 10 μ) were analyzed.
Abstract: Mie theory angular scattering distributions for spherical particles of refractive index m = 1.2 (0.2) to 2.4 and 2 − i, and of size 0.1 1μ then varies little with m for 1.4 10 μ at least, but as much flux may be received from absorbing as from transparent particles. In instruments measuring the forward lobe of the scattering pattern the differences in response for transparent and absorbing particles are least, but not negligible, and the collection of this lobe is difficult for particles larger than a few microns. Axially symmetric instruments do not necessarily measure forward scattering. No single instrument design can meet all requirements of aerosol measurement.
TL;DR: In this article, a cross-beam analysis of the angular distribution of the alkali halide product indicates that in all these reactions the final relative translational kinetic energy of the products is comparable to the initial kinetic energies of the reactants.
Abstract: Crossed-beam studies have been made of reactions of alkali atoms with about fifteen different halogen compounds. Kinematic analysis of the angular distributions of the alkali halide product indicates that in all these reactions the final relative translational kinetic energy of the products is comparable to the initial kinetic energy of the reactants. This has been confirmed for the K + Br2 reaction by direct velocity analysis of the KBr. Thus most of the chemical energy released (difference in strength of the new and old bonds) appears as internal excitation of the products. In some cases rotational and/or electronic excitation could be important; however, indirect arguments suggest that vibrational excitation of the newly formed bond is often dominant, at least for the reactions of alkali metals with diatomic halogen molecules. For these reactions, the cross section σr varies from
<∼10A2 to
>∼100A2. As σr increases, the favored direction for recoil of the alkali halide product gradually shifts from backward (rebound mechanism) to forward (stripping mechanism) and the angular distribution of alkali atoms scattered without reaction shows an increasingly pronounced fall-off at wide angles. These correlations and the product excitation are discussed in terms of simple models for the reaction dynamics.
TL;DR: In this paper, a useful polarizer for the 6-μ to 20-μ region has been designed, fabricated, and tested, and a microscopic wire grid was formed by ruling Irtran 2 (ZnS) or ZnSe(ZnSe) and evaporating aluminum preferentially on the groove tips.
Abstract: A useful polarizer for the 6-μ to 20-μ region has been designed, fabricated, and tested A microscopic wire grid was formed by ruling Irtran 2 (ZnS) or Irtran 4 (ZnSe) and evaporating aluminum preferentially on the groove tips The average transmittance for the crossed polarizers in the 8-μ to 20-μ region was less than 1% The degree of polarization was insensitive to a wide range of incidence angles Data showing the spectral polarization efficiency as a function of wavelength are presented
TL;DR: The most successful method of preparing highly efficient solar absorbers is to evaporate multilayer optical coatings on highly reflective substrates as mentioned in this paper, which consist of semitransparent metal films between nominally one quarter wave thick dielectric spacer layers.
Abstract: There are several uses in space for high-temperature coatings which selectively absorb solar energy but do not radiate much infrared energy. The most successful method of preparing highly efficient solar absorbers is to evaporate multilayer optical coatings on highly reflective substrates. These multilayer coatings consist of semitransparent metal films between nominally one quarter-wave thick dielectric spacer layers. Four such coating systems with 540°C space-stable properties ranging from a solar absorptance of 85% and emittance of 6% to a solar absorptance of 91% and emittance of 16% are presented.
TL;DR: In this paper, a differential pumping system for use with the argon emission continuum has been developed for photoelectric and photographic detection, order separation, and production of wavelength standards in the vacuum ultraviolet.
Abstract: Microwave-excited emission continua in rare gas (Xe, Kr, Ar) discharges have been investigated with respect to their suitability for photoelectric and photographic detection, order separation, and production of wavelength standards in the vacuum ultraviolet. A differential pumping system for use with the argon emission continuum has been developed. Absorption spectra of the following molecules are included here as examples of the usefulness of these radiation sources: O2, N2, CO2, C2H2, H2, and CO.
TL;DR: In this article, the scattering and absorption properties of concentric spherical water and soot particles have been investigated for visible and infrared wavelengths based on the theory by Aden and Kerker.
Abstract: Based on the theory by Aden and Kerker, computations of the scattering and absorption properties for concentric spherical water and soot particles have been performed for visible and infrared wavelengths. The complex dielectric constant for the kernel was assumed to be frequency independent; for the water shell it was assumed to be constant over the visible range only. Computations were performed for size parameter values up to 250. Results indicate that, for compound particles with a nucleus smaller than about one-tenth of the total diameter of the particle, the optical properties are almost completely determined by the outer shell.
TL;DR: In this article, a general theory of partial and complete vibrational-rotational population inversion is developed, and the equations governing partial inversion are illustrated for the example of HCl.
Abstract: A general theory of partial and complete vibrational-rotational population inversion is developed. The requirement for stimulated emission in the R-branch is that the rotational quantum number J shall exceed a minimum value which depends in a simple fashion on the ratio of the rotational to the vibrational temperature (Tr/Tυ), both of which may be positive (partial inversion). Stimulated emission in the Q and R branches is only possible if Tυ < 0 (complete inversion). Features peculiar to a vibrational-rotational laser are discussed in terms of the equation for net gain. Rough upper limits are set on the power output from a chemical laser. The equations governing partial inversion are illustrated for the example of HCl. Processes (electric discharge, chemical reaction) which have produced partial population inversion are discussed. The problem of maintaining complete population inversion is set out in terms of a hypothetical process forming CO continuously in level υ = 7 only. Physical processes which might excite a molecule into a high vibrational state either by way of an electronically excited state (through fluorescence) or within the ground electronic state (through electronic → vibrational transfer, or through energetic impacts) are discussed. Chemical processes which might result in a greater probability for reaction into a higher vibrational state than a lower one, kυ′ ≫ kυ, are considered under three headings: attractive, mixed, and repulsive reactions. (a) In attractive reactions it is supposed that the reagents attract but the products do not repel (significantly); the heat of reaction is trapped as vibration in the new bond. (b) In the mixed reactions it is argued that there is a tendency for the repulsion to be dissipated while the new bond is still extended; as a result, both repulsion and attraction could be converted to vibration in the new bond. (c) The repulsive reactions only appear likely to give kυ′ ≫ kυ in special circumstances; if the central atom is light or the repulsion impulsive. Examples are suggested in each category: (a) association reactions; (b) covalent → ionic reactions (e.g., alkali metal atom plus halogen or halide); (c) covalent reactions. The second category shows particular promise of providing reactions suitable for use in a chemical laser.