Showing papers on "Diffraction grating published in 1978"

Rigorous diffraction theory for transmission phase gratings with deep rectangular grooves

Abstract: The diffraction of light by deep rectangular-groove transmission phase gratings is treated by solving Maxwell’s equations numerically. Results are given for the light diffracted into the zero order by gratings with grating constants d in the range λ < d < 5λ, aspect ratio b (= linewidth/d), 0 < b < 1, and grating depths a < 5λ, assuming a refractive index n0 = 1.5. Such gratings are used in practice as a dye-free replacement for color filters. They offer a new way of storing pictorial information in small format for read out in conventional projectors.

A new general integral theory for dielectric coated gratings

Abstract: We present a new rigorous integral formalism for the theoretical study of dielectric coated gratings and grating couplers. It applies in the resonance domain, where the wavelength of the incident field and the groove spacing are of the same order of magnitude. The computed program issued from this theory extends the domain of application of the previous differential or integral theories. It can be used to investigate, with a very good accuracy, the properties of bare or dielectric coated gratings, for any groove shape and any polarization, in the entire visible, ultraviolet, and infrared regions. Various classical criteria are used to control the validity of the numerical results and comparisons are made with the numerical results obtained using the previous integral and differential formalisms. Two examples of applications are given. First, we show that the new possibilities of our program lead to a better agreement between theoretical results and experimental data. Second, a theoretical study of a certain type of grating coupler is given.

Diffraction efficiencies of thin phase gratings with arbitrary grating shape

Abstract: Diffraction by thin refractive-index gratings of arbitrary periodic shape is treated. Three analytical approaches are indicated and are shown to be equivalent. Resultant expressions for the diffraction efficiencies are given for all diffracted orders.

Color separation gratings.

Abstract: Special phase gratings are described by means of which the red, green, and blue color components of colored objects are generated side by side around the optical axis in the image plane of a lens. An analysis of these color separation gratings is given, and theoretical and experimental results for some grating samples are presented.

Solar power system

Abstract: A system for generating electrical power from sunlight, comprising a focussing diffraction grating or other focussing, spectrally dispersive means and a photocell array. The diffraction grating focuses sunlight into a spectrally dispersed band. The photocell array is composed of cells with different spectral sensitivities, located in positions in the dispersed band corresponding to the cell spectral sensitivities so that the net conversion efficiency of sunlight to electricity exceeds the conversion efficiency attainable with nondispersive collectors and single material photocells. Alternate embodiments of the invention provide sun tracking means, reflective or transmissive diffraction gratings, flat or curved diffraction grating surfaces, on- or off-axis focus, and optical coatings on the photocell surfaces.

On the use of classical and conical diffraction mountings for XUV gratings

Abstract: A description is given of the properties of plane diffraction gratings used in conical diffraction. Formulas are given for computing the direction of the diffracted orders. Experiments were performed to investigate the behavior of gratings used on conical diffraction mountings. Comparisons made with classical diffraction mountings show a significant increase in the efficiency of the -1 order. An empirical formula to predict the efficiencies of gratings used in conical diffraction mountings has been verified by the measurements.

Resist development control system

Abstract: RESIST DEVELOPMENT CONTROL SYSTEM Abstract of the Disclosure In the process of developing exposed photoresist on a substrate, the endpoint in developing away all of the exposed positive photoresist or any other positive resist is detected by exposing a wafer with a predetermined pattern including an optical grating or other special pattern formed in the photoresist upon a test area. In a system employing this concept, a beam is diffracted by the optics of the grating only at a first angle until the resist forming the grating is removed by development. Then a sensor is activated when an angle of reflection is unblocked when the grating dis-appears. The system is then turned off to stop development by the sensor in an automatic system or, by the operator in a manual system. A double exposure technique is employed to produce the grating or other special pattern.

Diffraction regimes of transmission gratings

Abstract: The diffraction characteristics of phase, absorption, and mixed transmission gratings of arbitrary thickness, modulation, and shape are treated. Single-wave, two-wave, and multiwave diffraction regimes are quantified and discussed. Boundaries between these regimes and their relationships to elementary “thin” and “thick” grating theories are presented.

Diffraction gratings for color filtering in the zero diffraction order

Abstract: Phase gratings with deep rectangular grooves have been successfully used in the zero diffraction order as transmission color filters. They form the basis of the ZOD microimage system for recording color images as surface-relief structures. ZOD images can be inexpensively replicated by hot embossing in a transparent sheet of plastic and read-out using conventional slide projectors or microfilm viewers. In this paper we use rigorous diffraction theory to derive optimum grating parameters for gratings with periods d < 2 μm to produce the three subtractive primary colors, cyan, magenta, and yellow, and also green. The theoretical results are in good agreement with the experiment.

Light valve, light valve display, and method

Abstract: A light valve comprises a pair of elements of transparent material each comprising a diffraction grating of like periodicity facing each other with parallel grating lines. Such a light valve is termed herein a bigrate. The transmission of light through the bigrate will depend on the relative position of the pair of gratings in the direction perpendicular to the grating lines and means may be provided for moving the elements relative to each other in that direction. One of the gratings may be embossed on a polyvinylidene fluoride (PVF 2 ) strip and moved by piezoelectric means, which may be a portion of such a strip. One strip may then be moved relative to the other in response to an electrical signal to control the zero diffraction order light transmission from no transmission to full transmission, or any desired intermediate transmission. Two intersecting sets of polyvinylidene fluoride (PVF 2 ) strips are arranged to form a matrix of bigrates, which, when uniformly illuminated produce a display of images, such as television images. In one set video signals produce motion perpendicular to the horizontal grating lines. The other set is made to move in a direction perpendicular to its surface in order to lock the strips of the first set in desired positions, or to unlock them, for example, a line at a time. Line-at-a-time TV signals may thus control the images. Three superimposed matrices each with diffraction lines of grating depth different from the others may provide color images.

Aberrations of a facet-type transmission grating for cosmic x-ray and XUV spectroscopy

Abstract: The aberrations of various types of curved constant-period transmission gratings are discussed, using Fermat’s principle. We show that optimal performance is achieved with a grating assembled from individual facets which form a nonclosed surface. For this geometry, primary coma and astigmatism are proportional to the facet size and, hence, may be adapted to the angular resolution of a Wolter-type telescope.

Simple selection rules for VUV and XUV diffraction gratings

Abstract: The bulk of diffraction gratings used in the VUV and XUV regions are used at small angles of incidence and have shallow groove depths. Using rigorous electromagnetic theory, it is shown that such gratings behave in a scalar manner. It is then possible to derive universal efficiency curves from which one can obtain with simple rules the efficiencies of gratings with any metallic surface. The role of standard dielectric overcoatings is investigated and is found to be small. Some comparisons with experiments are given.

Theory of crossed-beam diffraction gratings

Abstract: The operation of crossed-beam gratings is analyzed in terms of diffraction efficiency and beam quality, following Solymar's method's General solutions for arbitrary beam widths, general beam profiles, and illumination with two beams are derived. A scheme for improving the beam quality of these gratings is proposed. The analysis should be useful in integrated optics for designing beam expanders, beam contractors, and mirrors, and for analyzing waveguide interferometers.

Rapid scan spectral analysis system utilizing higher order spectral reflections of holographic diffraction gratings

Abstract: An improved optical system is disclosed for rapid, accurate spectral analysis of the reflectivity or transmissivity of samples. A concave holographic diffraction grating oscillated at high speed is utilized to provide a rapid scanning of monochromatic light through a spectrum of wavelengths. The grating is positively driven at very high speed. The rapid scan by the grating enables the reduction of noise error by averaging over a large number of cycles. It also reduces the measurement time and thus prevents sample heating by excessive exposure to light energy. A filter wheel having opaque segments is rotated in the optical path and is synchronous with the grating. The filter wheel is divided into two arcuate segments separated by the opaque segments arranged approximately 180 degrees apart. One arcuate segment of the wheel transmits only first order light. The other arcuate segment transmits only second order light. Separate photodetectors are employed during infrared analysis of samples for detecting first order and second order wavelength transmissions and an electronic decoder apparatus is utilized for switching between detectors.

Radiation beam deflection system

Abstract: Apparatus for deflecting a beam of electromagnetic radiation controllably such that the beam can be used for scanning and other purposes. In this invention, the output beam of the apparatus is deflected by a dispersion element such as a diffraction grating, the angular deviation induced by the grating being a function of the wavelength of the radiation. Variations in the deflections induced by the deviation element to thereby cause a controlled angular movement of the output beam are produced by varying the wavelength of the radiation. These variations in the wavelength of the radiation are produced in several embodiments by a multiplicity of radiation sources, each having an energy output of a discrete wavelength, and in further embodiments by means such as a parametric converter which vary the wavelength of the source. Energy from the zero order of the radiation from the first dispersion element is deflected by a second dispersion element in accordance with the wavelength of the radiation in synchronism with the principal output beam. This second deviated beam is tracked by radiation sensors which form part of a feedback circuit in the control system of the scanner.

A New Formalism for Transmission Gratings

Abstract: A new formalism for diffraction gratings consisting of a single grating surface surrounded by a number of planar films is presented. The diffraction problem is shown to reduce to the solution of a Fredholm integral equation of the first kind. The numerical implementation has been thoroughly tested using the constraints of energy conservation and reciprocity. A new constraint relating the phases and efficiencies of the propagating orders excited when a lossless symmetric transmission grating is operated in a first-order Littrow mount has been derived theoretically and verified numerically. The theory has been used to optimize the selective performance of a solar absorber consisting of a thin graphite layer deposited on a copper substrate. The superposition of a grating absorption feature on the primary resonance minimum of the absorptivity curve is shown to improve the integrated absorptivity by approximately 10 per cent.

Comprehensive analysis of gratings for ultraviolet space instrumentation

Abstract: Comprehensive measurements in the vacuum uv range of 1200-3000 A of efficiency, polarization, and scattering of classically ruled and photoresist gratings are reported. The results show that the art of ruling gratings for vacuum uv use has reached a high level of sophistication and that careful analysis of grating properties can lead to useful improvement of the ruling art.

On an asymptotic theory of diffraction gratings used in the scalar domain

Abstract: Starting from the electromagnetic theory, we derive an asymptotic formalism to investigate the behavior of perfectly conducting gratings used at small wavelengths to groove pitch ratios and near normal incidence. The theory is applied to study three classical types of profiles: sinusoidal, lamellar, and blazed gratings. Results are given for both −1 and −2 Littrow (or near Littrow) mounts. The accuracy of the theory and the limits of the domain where it applies are studied by the use of rigorous electromagnetic computations. The role of a finite conductivity of the surface is also investigated.

Device for coupling at least three light guides

Abstract: The invention provides a coupling device for monochromatic optical signals based on the amplitude division method. The optical signal emerging from one light guide is divided by means of one or more diffraction gratings among three or more outgoing light guides. Inversely, the optical signals from a number of light guides can be combined into one optical signal. Such a coupling device has a high optical efficiency, is mode-independent and produces small differences in light intensity between the branch signals.

Optically measuring the carrier concentration in a semiconductor

Abstract: A method of optically measuring the concentration of carriers in a doped region of a semiconductor wafer includes the step of selectively introducing conductivity modifiers into both the wafer and a test substrate simultaneously to form respectively the doped region in the wafer and a diffraction grating pattern in the substrate including periodically-spaced doped strips. The diffraction grating pattern is exposed to a beam of monochromatic light, and the intensity of one of the diffracted beams is measured, whereby the magnitude thereof is a measure of the carrier concentration in the doped region.

Scattering phenomena in volume holograms with strong coupling.

Abstract: A qualitative analysis of various diffraction phenomena, visible in scattering volume gratings, like scattering rings, Kossel lines, dark scattering rings, is made for gratings including higher order harmonics and for gratings with strong coupling. An interference phenomenon, explained by the dynamical theory of diffraction, is demonstrated. In order to simplify the analysis of these phenomena and diffraction in volume gratings in general, a modification of the traditional Ewald construction is introduced. This modification is geometrically equivalent but physically more consistent and, for instance, defines how the observer is related to the wave vector sphere and also permits the location and extent of the intermodulation spectrum to be easily constructed. The construction is applied to the recording and readout of multiple recording by superposition in volume holograms as an illustration.

A Low-Loss Diffraction Grating Frequency Multiplexer

Abstract: A quasi-optical frequency multiplexer based on a blazed diffraction grating is studied. Experimental data, supported by semi-quantitative theoretical considerations, show that the multiplexer is an efficient channel-dropping filter well suited to use in the millimeter wave region. A feature of the grating multiplexer which sets it apart from conventional designs is its ability to drop several channels using a single frequency-selective element, namely, a diffraction grating. This economy of hardware results in a simple, compact structure. The channels of the experimental multiplexer have typical bandwidths of ~540 MHz with loss of ~1 dB. The width of the impulse response at half amplitude is ~1.5 ns. Return loss within a channel is typically 15-20 dB. Comparisons with other millimeter wave multiplexer designs are discussed.

Pulsed ir holography on Takiwax films.

Abstract: Phase holograms have been recorded on Takiwax films with pulsed TEA CO2 laser light. The reconstruction from these phase holograms is accomplished by transmission at a wavelength of 0.633 μm. Holographic characteristics of the recording medium, such as diffraction efficiency vs film thickness, exposure, and spatial frequency, are presented. The capability of Takiwax films to record ir holograms of plane objects and double-exposure holographic interferograms is demonstrated.

Large aperture phased element modulator/antenna

Abstract: An electro-optical modulator/antenna operates in the tunable diffraction ting mode to vary the magnitude of the zero diffraction order and consequently transmits optical information. A relatively thin slab of lithium niobate or equivalent electro-optic material has its lateral surfaces optically polished and its C-axis, or optical axis, running parallel to the polished lateral surfaces. At least one set of interdigital metallic electrodes are deposited on the face or just within the lateral surfaces to form, among other things, a diffraction grating that is orthogonally disposed with respect to the C-axis. When a potential source is coupled to the interdigital electrodes, the electric fields between adjacent electrodes change the crystal's index of refraction in accordance with the linear transverse Pockel's effect. The thin crystal having the electrodes substantially covering at least one of its lateral surfaces, thusly presents a large aperture modulator/antenna capable of modulating incident optical energy over a wide angle of incidence, for example, up to plus and minus 45 degrees. Because of the thinness of the crystal, transmissivity is good and losses are reduced. The cooperation between the diffraction grating phenomenon and the Pockel's effect greatly reduces if not totally eliminates the possibility of arcing between adjacent electrodes as the zero diffraction order is modulated since the potentials creating the modulating electric fields between adjacent interdigital electrodes are greatly reduced in this mode of operation.

High-dispersion astronomical spectroscopy with holographic and ruled diffraction gratings

Abstract: Holographic gratings cause much less stray light and spectral degradation than classically ruled gratings. Their high groove densities enable high dispersion in first diffraction order and a high spectrograph through-put comparable to the best echelles. Their lower reflective efficiency is compensated by the avoidance of cross dispersers, enabling efficient high-fidelity spectroscopy with single-pass spectrographs. Instrumental profiles of the ESO coude spectrograph with large holographic and ruled gratings have been studied in detail, and their effects on astronomical spectra are discussed and compared to those of other instruments.

Theory of alignment monitoring by diffraction from superimposed dual gratings

Abstract: Theoretical considerations are presented on characteristics of the optical-alignment technique using dual gratings. The general formulation of the diffraction pattern is derived for superimposition of dual amplitude–phase gratings, as functions of aperture ratios for gratings and separation gaps between dual gratings. Numerical analyses reveal characteristics for precise positioning control or alignment technique, which utilize the detection of the minimum value of the first-order diffraction beam or the detection of the zero cross point of the difference in intensities between +1- and −1-order diffraction light for dual gratings. Alignment errors due to variations in an incident light angle, displacement in detector position, and fabrication errors for the gratings are also discussed.