Showing papers on "Diffraction grating published in 1981"

The Dielectric Lamellar Diffraction Grating

Abstract: A rigorous modal theory describing the diffraction properties of a dielectric lamellar grating is presented. The numerical implementation is shown to be suited to modelling the behaviour of high refractive index gratings. This suggests that an approach of this type may be successfully applied to the problem of lossy metallic lamellar gratings.

Novel geometry for single-mode scanning of tunable lasers

Abstract: We describe a geometry that allows for the single-mode scanning of lasers that use a diffraction grating as the dispersive element. It is observed that under the right conditions a rotation of the tuning element can provide changes simultaneously in cavity length and diffraction angle that exactly match the requirements needed for continuous single-mode scanning. As a case study, the method is applied to the grazing-incidence pulsed dye laser.

Image display apparatus of liquid crystal valve projection type

Abstract: A liquid crystal light valve projection type image display apparatus comprises an electro-optic element and a Schlieren optical system. The electro-optic element has a liquid crystal layer having a dielectric and optical anisotropy. An electric field having a spatial intensity distribution according to an image signal is applied to said liquid crystal at a spatial period, so that a spatially phase-modulated phase diffraction grating is formed in the liquid crystal layer. Thus, a projected image in enlarged form is obtained. The fact that the electric field with a spatial period is applied to the liquid crystal leads to a constant light diffraction angle, and the modulation of the diffraction light intensity in the applied electric field enables an image corresponding to the input image signal to be projected at high light utilization.

The Finitely Conducting Lamellar Diffraction Grating

Abstract: A rigorous modal theory describing the diffraction properties of a finitely conducting lamellar grating is presented. The method used is the generalization to lossy structures of an earlier formalism for the dielectric lamellar grating. Sample results of the method are given, demonstrating its accuracy and its ability to deal with problems intractable by the widely used integral-equation formalisms of diffraction grating theory.

Optical scanning system with wavelength shift correction

Abstract: A spot scanning holographic spinner system incorporates an optical element in the optical path to provide compensation for wavelength shifts in the coherent light source. The device is located in a plane parallel to the spinner and consists of a diffraction grating having the same properties as gratings formed on the spinner surface.

Highly Conducting Lamellar Diffraction Gratings

Abstract: We outline an improved root-finding algorithm necessary for the solution of the eigenvalue equation associated with the diffraction formalism for lossy lamellar gratings. A numerical example is presented, demonstrating the adequacy of this technique for a highly-conducting aluminium grating.

Planar Rowland spectrometer for fiber-optic wavelength demultiplexing

Abstract: A planar Rowland spectrometer was fabricated and characterized as a wavelength demultiplexer for multimode fiber-optic applications. The spectrometer consisted of a planar multimode glass waveguide with two curved end faces and a cylindrical concave attached to one of the end faces. Semiconductor lasers with wavelengths between 0.825 and 0.845 micron were used for the measurements. Cross-talk isolation between two adjacent fibers with center-to-center separation of 175 microns (100 A in wavelength difference) was measured to be 18 dB. The device's performance was limited by grating diffraction efficiency, optical aberration, waveguide dispersion, and waveguide losses.

Millimeter-wave orotron oscillation - Part I: Theory

Abstract: Physical principles of operation of the orotton, a Smith-Purcell free-electron laser in the millimeter and submillimeter wavelength regions, are described. Electron bunching in this device occurs when the electron beam interacts with an evanescent component of the electromagnetic wave that propagates along the metallic diffraction grating of the device with a phase velocity neatly equal to the electron velocity; this bunching produces coherent radiation. The equations of motion are linearized, and the starting current and electronic tuning characteristics of the device are calculated in closed form. Numerical calculations of the electron efficiency are described.

Formation of holographic diffraction gratings in photoresist

Abstract: The exposure-development process for the fabrication of holographic diffraction gratings for integrated optics in the positive photoresist Shipley AZ-1350 is theoretically and experimentally investigated. An analysis of the light intensity distribution is carried out, taking into account the reflectivity at the photoresist-substrate interface and the attenuation in the photoresist for two holographic exposure arrangements. The influence of the exposure energy, the development time for a fixed concentration of the developer and the initial photoresist thickness are described. Various grating profiles are calculated for photoresist films, coated on matched and reflective substrates. Scanning electron micrographs demonstrate very good agreement between the actual and calculated gratings profiles.

X-ray monochromator designs based on extreme off-plane grating mountings.

Abstract: Several monochromator designs are presented in which the beam is incident on the grating nearly parallel to the grooves. The efficiency of such mountings, when obeying the blaze condition, is much higher than that of classical arrangements. Because only the Snell's components of the angular coordinates are varied, this high efficiency is found over the complete wavelength range. With the designs described the wavelength region from 0.6 to 100 nm can be covered without interchanging gratings. For each wavelength the spectral resolution can be increased to ~10(4). Entrance and exit slit positions and the corresponding beam orientations are fixed.

Optical grating using a liquid suspension of dielectric particles

Abstract: The invention provides apparatus comprising at least two beams of coherent radiation directed so as to intersect and form a standing wave pattern having a period Λ in an optically responsive medium. The optically responsive medium is a colloidal suspension of dielectric particles in a liquid medium, the dielectric particles and liquid having different indices of refraction, and the diameter of the particles being less than or approximately equal to the period Λ. The dielectric particles are arranged into a grating by the electric fields carried by the beams of coherent radiation. In an embodiment of the invention, the dielectric particles are small dielectric spheres. The dielectric particles and the liquid may have approximately equal mass densities. A third beam of light may generate an output beam of light by degenerate four-wave mixing processes incorporating a dielectric grating made by the electric fields carried by the beams of coherent radiation.

Gold transmission gratings with submicrometer periods and thicknesses ≳0.5 μm

Abstract: Gold gratings with spatial periods of 0.3 and 0.2 μm have been fabricated in thicknesses of 0.6 and 0.25 μm, respectively, and used in x‐ray spectroscopy and spatial‐period‐division. Fabrication techniques included: holographic lithography, shadowing, x‐ray lithography, and gold microplating. Control of linewidth to tolerance of the order of 10 nm has been demonstrated for gratings of 0.2 μm period. A high resolution imaging spectrometer, composed of a 22× Wolter x‐ray microscope in conjunction with a gold transmission grating, was tested. At a wavelength of 0.69 nm, a resolving power, λ/Δλ, of 200 was demonstrated. Resolution in this case was source‐size limited. Gratings of 99.5 nm period were exposed in PMMA by x‐ray (λ = 4.5 nm) spatial‐period‐division.

Recording of phase-amplitude images.

Abstract: An interferometer comprising three diffraction gratings and an imaging system is used with spatially and spectrally noncoherent light to produce high fidelity low noise recording of phase- and -amplitude objects.

Diffraction Gratings Ruled And Holographic - A Review

Abstract: Diffraction gratings have been evolving steadily over the last ten years. Modern ruling engines have permitted classically ruled gratings to be more efficient with flatter diffracted wavefront than ever before. Examples include sophisticated laser gratings with up to 97.5% efficiency and flatness of better than λ/3 in 17th order 6328X. Holographically recorded diffraction gratings continue to evolve with the development of blazed plane gratings and with groove densities of up to 6000g/mm. Concave holographic gratings now range from toroidal aberration corrected gratings,for use in the soft x-ray, to flat field spectrographs and scanning spectrographs operating out into the infra-red.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Absolute S- and P-plane polarization efficiencies for high frequency holographic gratings in the VUV.

Abstract: High frequency plane gratings (3500 and 3600 gr/mm) have been holographically ruled and blazed for the VUV spectral region. All gratings were coated with 70 nm Al + 25 nm MgF2. Absolute unpolarized and S- and P-plane polarization efficiencies have been measured for the first and second orders in the 120- to 450-nm spectral region at 18.5 and 30 deg angles of deviation. For deep grooves, anomalous features are more pronounced for the P-plane polarization efficiency than for the S-plane polarization efficiency. Holographic gratings can be tailored to produce high polarization or low polarization in the VUV. For comparison, efficiencies and polarization of the best conventional high frequency gratings were also determined. Measurements show that scattered light is significantly lower for holographic gratings in the VUV when compared with the conventional gratings.

Solar cell with reflecting grating substrate

Abstract: A solar cell which includes a thin layer of active material bounded on the side toward the incident light with an antireflection coating and bounded on the other side by a reflecting diffraction grating to internally reflect the incident light back into the active material.

Diffracted energy auto-ranging system for a camera

Abstract: An infra-red auto-ranging system for a photographic camera or the like includes a ranging sensor that directs a portion of the light energy from the subject of principal interest through a diffraction device that diffracts the radiation into central and higher order spectral lines that are then passed through an infra-red filter. An infra-red responsive sensor, such as a photo-responsive reticon array, is positioned to receive the radiation from a selected one of the spectral lines with the position of the imaged spectral energy on the sensor varying as a function of the angle of incidence of the light from the subject and of the range to the subject. The diffraction device may take the form of a conventional transmission-type diffraction grating, a replica, or an acousto/optical diffraction cell responsive to an excitation energy source. Computing circuitry is provided to determine the range to the subject of principal interest as a function of the position that the selected spectral line images on the sensor. By appropriate selection of the diffraction characteristics of the diffraction device, it is possible to limit the width of the selected spectral line to a narrowly defined physical limit to enhance the resolution of the ranging determination.

Optical fluid analyzing apparatus and method

Abstract: An optical fluid analyzing apparatus is shown comprising transparent means (12,13) of known refractive index (n1) providing a cell (14) for receiving a fluid sample of unknown refractive index (n2). A diffraction grating 10 is formed in an inner wall (11) of the cell. A light source (15) is positioned at an incident angle (θ0) with a grating to satisfy the Bragg condition. A pair of detectors (16, 17) intercept the 0th order and 1st order diffracted light. Circuitry (18) responds to signals generated by the detectors to provide an output indicative of the refractive index of the sample.

Device for measurement of the torsional angular deviation of a loaded rotating or static shaft

Abstract: A torsional angular deviation measuring device comprising a first diffraction grating which is placed at one end of a shaft and a second diffraction grating placed at the other end or at least some distance from the first end. A beam of light from a light source is then passed through the first diffraction grating generating zeroth order and other order beams. The beams are thence passed through collimating optics and then through the second diffraction grating. The beams from the second diffraction grating are sensed by split photodiodes and the amount of angular deviation is then measured by comparing the phases of pulse trains generated from the different photodiodes with one another.

Angle-Resolved Light Scattering From Composite Optical Surfaces

Abstract: Described here is the derivation of an expression designed to predict the angular distribution of light scattered from composite surfaces. The scattering is assumed to be the result of microroughness, either periodic or random, present at each interface of the composite surface. The theory retains the vector nature of the fields and allows complex optical constants. The angles of incidence and scattering or diffraction are arbitrary. The number and thicknesses of the layers in the composite surface are arbitrary. The primary restriction on the validity of the theory is that the incident wavelength λ >>δ where δ represents the root mean square (rms) roughness of any interface. This restriction therefore precludes the application of this theory to high-efficiency gratings. However, low-efficiency gratings, such as those designed for beam sampler applications, fall within the validity of the theory. Also, high quality optical components, such as laser gyro mirrors, typically have rms roughness values much less than a wavelength. Various aspects and applications of this theory have been published previously.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Flat Field Imaging Spectroscopy Using Aberration Corrected Holographic Gratings

Abstract: In this paper it will be seen that an aberration corrected holographic diffraction grating can function as the sole optical component in a spectrograph The use of such a grating has shown that over a flat focal plane, resolution was maintained In the examples described, two gratings were tested; one of which operated in the range of 2000-8000A, the other 4000-8000A, each range distributed over 25mm Resolution was found to be constant up to lmm on each side of the optical axis perpendicular to dispersion, permitting spatial resolution with wavelength The device is reviewed in terms of its applications in astronomy and analytical spectroscopy© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Variation of blaze of concave diffraction gratings.

Abstract: The change in blaze wavelength as a function of position on a blazed concave diffraction grating surface is discussed. An experimental study of ruled and interferometric blazed concave gratings showed that the change in blaze across the grating surface is much less for an interferometric grating than for a ruled grating. Thus interferometric gratings can be expected to have a more uniform distribution of efficiency across their surfaces.

X-Ray encoding system using an optical grating

Abstract: X-ray information is encoded onto photographic film by placing an optical grating between the light-emitting scintillating screen and the photographic emulsion. Information at different energies is encoded by displacing the grating between exposures or by using static gratings with an energy-selective dual screen.

Grazing angle tuner for cw lasers

Abstract: The use of a grazing angle grating tuner for single-mode operation of a color center laser is described. Design criteria are developed for optimizing the output coupling and wavelength dispersion while maintaining high efficiency.

Monochromatic imaging apparatus

Abstract: A monochromatic imaging apparatus comprising a pair of similar diffraction gratings, a pair of focusing lenses, a pair of collimating lenses, an entrance slit, an exit slit and an intermediate slit, and means for concurrently moving the two gratings; wherein a polychromatic source image is placed at the entrance slit, and a collimating lens collimates the light rays from the source image and projects the collimated rays onto the first diffraction grating thereby to disperse the rays. The dispersed rays are then focused by the first focusing lens onto the intermediate slit, and then collimated by the second collimating lens onto the second diffraction grating which thereupon recombines the dispersed light. The recombined rays are then focused by the second focusing lens onto the exit slit. The two gratings may be concurrently moved in opposite or similar directions about an axis in the grating ruling plane and at the centers thereof, and at similar angles, so that the angle of incidence at the first grating is equal to the angle of diffraction at the second grating. In this manner, a monochromatic image of the polychromatic source image will appear at the exit slit and be of a selected band of wavelengths of the visible or other spectrum dependent upon the angular position of the two gratings from zero order of diffraction.

Echelle and holographic gratings compared for scattering and spectral resolution

Abstract: An echelle grating with 316 grooves/mm and a 63° blaze angle is compared with a 3600-groove/mm holographic grating. The scattered light and resolution of the 10- × 20-cm gratings are photoelectrically evaluated in a 3-m spectrometer optimized to eliminate coma and baffled to minimize instrumental scattered light. Both gratings are ghost-free, but the holographic grating has substantially lower scattered light for test lines near 4000 A and yields improved stray light rejection within absorption lines. It also exhibits slightly higher resolution. The throughput of the spectrometer with the holographic grating is about 5 times higher than the equivalent combination of spectrometer, echelle grating, and predisperser.

Method of moire-metrical testing of optical imaging systems

Abstract: A method for testing optical imaging systems by the use of moire stripes, wherein two copies of an optical grating are made and simultaneously illuminated to produce a moire pattern which is a measure of the distortion of the imaging system. In a first step an original grating is transferred by a light beam as a contact copy onto a substrate. In a second step, the imaging system to be tested copies the original grating for a second time onto the substrate, except that the second grating copy is rotated slightly with respect to the first grating copy. The points of intersection of the two superimposed gratings produce moire stripes when illuminated, the positions of the stripes being calculated precisely with the assumption that ideal gratings were used. If the imaging system to be tested shows distortions, the position of the moire stripes that are observed will not correspond to these calculated positions. The deviation therefrom is a measure of the imaging system errors.

Extreme ultraviolet transmission grating monochromator.

Abstract: A compact monochromator has been designed to utilize recently developed free-standing XUV transmission gratings. Tests using a condensed spark source of far UV radiation show that this monochromator, with 20-μm slits, is capable of 0.08-nm resolution at 30 nm in the first order. A physical description of the system and test results are presented.