Showing papers on "Diffraction grating published in 1983"

10 kHz linewidth 1.5 μm InGaAsP external cavity laser with 55 nm tuning range

Abstract: An InGaAsP 1.5 μm laser, with one facet antireflection coated, has been incorporated into a diffraction grating external cavity. The lasing wavelength could be tuned over a 55 nm range about the centre wavelength of 1.5 μm by rotating the grating. Furthermore, it was found that the emission spectrum was extremely narrow; beat-frequency measurements at 1523 nm against an HeNe laser showed it to be of the order of 10 kHz.

Rigorous coupled-wave analysis of grating diffraction— E-mode polarization and losses

Abstract: Rigorous coupled-wave theory of diffraction by dielectric gratings is extended to cover E-mode polarization and losses. Unlike in the H-mode-polarization case, it is shown that, in the E-mode case, direct coupling exists between all diffracted orders rather than just between adjacent orders.

Analysis of anisotropic dielectric gratings

Abstract: A method for analyzing slanted anisotropic gratings is presented. The propagation of electromagnetic waves in the periodic anisotropic media is described by coupled-wave equations in a unified matrix form expressing the coupling of the space harmonics in the grating region. The solution of the equations is reduced to an eigenvalue problem of this coupling matrix. Through introduction of the concepts of transmission and boundary matrices, the diffraction properties of general slanted gratings are obtained rigorously by systematic matrix calculations that are easily implemented on a computer. The calculated results indicate that not only TE–TE or TM–TM but also TE–TM diffractions take place in general slanted gratings.

Variable line-space gratings: new designs for use in grazing incidence spectrometers.

Abstract: An account is given of a fundamentally different approach to the use of variable line-space gratings for grazing incidence spectrometers. In the new approach, the gratings are flat and they are placed to intercept the converging beam from a collecting mirror rather than the diverging beam from a slit. This results in (1) small aberrations over a wide instantaneous range in wavelength, (2) a modest required variation in line spacing across the ruled width, (3) a simultaneous minimization of both the spectral and image height aberrations, and (4) a completely stigmatic zero order image. The slitless arrangement common to these designs is very compact, having no additional length behind the focal plane of the collecting mirror. In-plane and conical fan designs are considered. One combination design, in the form of an echelle spectrometer, is discussed. The designs are considered to represent ideal candidates for moderate to high resolution spectrometers on such missions as the Far Ultraviolet Spectroscopic Explorer (FUSE, now Columbus) and the Advanced X-ray Astrophysics Facility (AXAF).

12× pulse compression using optical fibers

Abstract: We report a factor of 12 compression of the 5.4‐ps, 1‐kW pulses from a mode‐locked dye laser. The pulses were frequency broadened and linearly chirped by the combined action of self‐phase modulation and group velocity dispersion during passage through a 30‐m single‐mode optical fiber. The fiber output pulses were then compressed to 450‐fs, 3‐kW pulses by passage through a diffraction grating based dispersive delay line. These short pulses were tunable over the 300‐A range of the laser dye.

Wafer/mask alignment system using diffraction gratings

Abstract: An alignment method in which light is diffracted from a mask grating to a wafer grating and back through the mask grating to produce a set of output diffraction orders. The intensity of the zeroth output order is monitored and the mask is translated and rotated within the plane containing the mask to align the mask with the wafer. Alignment occurs when the intensity of the zeroth output order is at an extremum. The distance between the mask and wafer is also adjusted to extremize the intensity of the zeroth output order to make the wafer lie within the focal plane of the exposure optics. The wafer mask is preferrably a holographic phase grating to simplify production of the grating and to eliminate resist related interference. Two dimensional gratings can be used to achieve alignment with only one grating on each wafer.

Incoherent Superposition of Multiple Self-imaging Lau Effect and Moiré Fringe Explanation

Abstract: Characteristics of the diffraction field of two spatially separated linear diffraction gratings under incoherent illumination are studied. The analytical model is based on the spatial superposition of many mutually incoherent Talbot (self-imaging) effects. It permits a simple explanation of the basic parameters of the ‘incoherent’ diffraction images: axial localization, spatial period and lateral displacement. The moire fringe formation in space, the imaging of a grating by a second grating, and the Lau effect are considered; the results are compared with the former studies in the literature.

Method of forming laser diffraction grating for beam sampling device

Abstract: A combined holographic grating that samples a high energy laser beam and focuses the sample into a spot is formed by the cross-modulation term of a linear holographic grating and a holographic zone plate

Time-resolved x-ray transmission grating spectrometer for studying laser-produced plasmas

Abstract: The development of a new time-resolved x-ray spectrometer is reported in which a free-standing x-ray transmission grating is coupled to a soft x-ray streak camera. The instrument measures continuous x-ray spectra with 20-psec temporal resolution and moderate spectral resolution (Δλ ≥ 1 A) over a broad spectral range (0.1–5 keV) with high sensitivity and large information recording capacity. Its capabilities are well suited to investigation of laser-generated plasmas, and they nicely complement the characteristics of other time-resolved spectroscopic techniques presently in use. The transmission grating spectrometer has been used on a variety of laser-plasma experiments. We report the first measurements of the temporal variation of continuous low-energy x-ray spectra from laser-irradiated disk targets.

Solar cell with two-dimensional hexagonal reflecting diffraction grating

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 two-dimensional hexagonal reflecting diffraction grating to internally reflect the incident light back into the active material.

Diffraction head up display solar radiation filter

Abstract: A diffraction grating head up display which blocks solar radiation from impinging upon and washing out the image of display information on an optical display device. This is accomplished by means of a filter such an optical element (12) made of photochromic material which is positioned between the display information surface (10) and relay optics lenses (14) preferably at the back focal plane thereof, so that focused solar radiation darkens a localized spot in the photochromic material. The darkened spot blocks the solar energy but reversibly lightens after the focused solar energy is removed. This photochromic material allow substantially unimpeded transmittance of the image of the display information except at the darkened spot. Also included in the optical system are a folding reflector (16) and a combiner lens element (18) which combines and superimposes the image of the display information on the scene being viewed when an observer looks through the combiner element (18). This combiner element (18) is a diffraction grating holographic lens which is reflective or diffractive of a narrow bandwidth of light which includes the narrow bandwidth light of the display information.

Optical device for use as a multiplexer or demultiplexer in accordance with the diffraction grating principle

Abstract: An optical device for use either as a waveguide demultiplexer or a waveguide multiplexer characterized by a compact transparent member having a surface forming optical means such as an imaging mirror, an opposite surface portion having a diffraction grating formed thereon and first and second coupling surfaces so that light can be coupled into the member reflected by the mirror and the diffraction grating and then coupled out of the member. The device has various embodiments with different structures for the optical mirror and the transparent member, with the structure of the coupling surfaces being flat or curved, and with either flat or curved additional mirrors for reflecting the incoming and outgoing light adjacent to the coupling surfaces.

X-ray spectrographs using radial groove gratings.

Abstract: A high efficiency spectrograph design for the EUV and soft X rays is presented. This grazing incidence system uses a plane surface reflection grating with rulings that are radial, like the spokes of a wheel. The grating is placed in a beam of light that is converging to a focus. The single reflection off the grating is in the conical diffraction mount ensuring maximum performance from the system. Aberrations and performance levels are discussed. The gratings can be manufactured with existing ruling engines. Sample applications to an X-ray monochromator and an EUV stellar spectrograph are discussed.

High-frequency holographic transmission gratings in photoresist

Abstract: This paper describes an experimental study of the diffraction properties of high-spatial-frequency gratings recorded in relatively thin photoresist layers. Angular selectivity, wavelength selectivity, and peak efficiencies are investigated. Details on grating fabrication are given. The study shows that optical elements with efficiencies greater than 88% can be recorded in media less than one wavelength thick (~0.5 μm for our visible-light experiments). The results are important in that such diffractive structures could be replicated by embossing, chemical-vapor deposition, or other means.

Interaction of electromagnetic waves with periodic gratings: Enhanced fields and the reflectivity

Abstract: We present results of calculations of the reflectivity of diffraction gratings of sawtooth profile, and of electric fields near such gratings. We employ a method based on the use of the extinction theorem, and the grating amplitude is not assumed small. This approach also allows one to calculate the electric fields within the selvedge region of the grating. We place emphasis on frequency regimes where the grating couples an incoming photon to a surface polariton on the grating. The implications of our results for the study of optical interactions on surfaces are discussed.

Opto-optical light deflection

Abstract: Light deflection is accomplished by diffraction from a transient index modulation established as a grating of variable frequency in an optical material by the interference of two controlling light beams. This device may be considered an opto-optical analog to an acoustooptical deflector, in that a change in angular deflection is created by altering the frequency of the diffraction grating. In this paper we report on a technique for altering the grating frequency by changing the wavelength of the control beams and the use of a novel optical system to maintain the Bragg condition over a wide range of frequencies. Configurations exhibiting very large angular deflections have been designed using a computer simulation and optimization program that allows minimization of the Bragg detuning. This new method of light deflection allows either discrete or continuous light scanning or modulation. A particular example using lithium niobate will be discussed which produces an 11.8° deflection from a 0.027-μm wavelength change and with an angular detuning of less than ±0.03°. The use of other materials, inorganic, organic, and dispersive, will also be discussed.

Submillisecond grating diffractions in nematic liquid crystal films

Abstract: We have quantitatively observed a large fast component in the laser induced thermal grating in nematic liquid crystal films. This effect can be successfully utilized in submillisecond and high spatial frequency four wave mixing processes with low power lasers.

Planar volume phase holograms formed in bleached photographic emulsions.

Abstract: Volume phase holograms are formed by a standard process in commercially available photographic emulsion. The material is characterized before recording, and initial experimental results are presented for reconstruction under index-matched conditions. An initial comparison is made using two-wave coupled-wave theory and a technique of curve fitting with experimental measurements of transmission and diffraction efficiency. The model works well close to the Bragg condition, but several differences are noted between theory and experiment away from the Bragg condition. An anomalous absorptive effect is noted in transmission. An improved model is then formulated, again using coupled-wave theory, and capable of analytic solution, taking into account phase and absorption modulation, a second harmonic in the grating profile and the appearance of some higher diffraction orders. Using this model, all the initial experimental results are satisfactorily explained, and the effect of spurious gratings in the hologram response is noted. The model is then used with an extensive set of experimental results to deduce the major characteristics of the material, including saturation of the modulation with exposure. The formulation of a mixed grating and possible dispersion of the modulation are also investigated. Suggestions are made for the design of more complicated components using this material and for material improvement.

On the numerical study of deep dielectric lamellar gratings

Abstract: This paper is related to a new method recently proposed by Australian authors for the study of lamellar gratings in electromagnetic theory. The present authors first recall the principle of this method and make some theoretical comments. Then they describe how numerical difficulties which appear in normal incidence and in Littrow mounts can be overcome.

Fraunhofer Diffraction Patterns of Titled Planar Objects

Abstract: Attention is drawn to the changes in the Fraunhofer diffraction patterns encountered when the planar objects become titled with respect to the optical axis. The differences between the far-field images observed in the well-known untilted case and the one investigated are shown and discussed using examples of familiar objects, such as square or rectangular apertures and linear diffraction gratings.

Scattering Theory for Diffraction Gratings

Abstract: 1. Physical Theory.- 1. The Physical Problem.- 2. The Mathematical Formulation.- 3. Solution of the Initial-Boundary Value Problem.- 4. The Reference Problem and Its Eigenfunctions.- 5. Rayleigh-Bloch Diffracted Plane Waves for Gratings.- 6. Rayleigh-Bloch Surface Waves for Gratings.- 7. Rayleigh-Bloch Wave Expansions.- 8. Wave and Scattering Operators for Gratings.- 9. Asymptotic Wave Functions for Gratings.- 10. The Scattering of Signals from Remote Sources.- 2. Mathematical Theory.- 1. Grating Domains and Grating Propagators.- 2. Rayleigh-Bloch Waves.- 3. The Reduced Grating Propagator Ap.- 4. Analytic Continuation of the Resolvent of Ap.- 5. Proofs of the Results of 4.- 6. The Eigenfunction Expansion for Ap.- 7. Proofs of the Results of 6.- 8. The Rayleigh-Bloch Wave Expansions for A.- 9. Proofs of the Results of 8.- 10. The Initial-Boundary Value Problems for the Scattered Fields.- 11. Construction of the Wave Operators for AP and Ao,p.- 12. Construction of the Wave Operators for A and Ao.- 13. Asymptotic Wave Functions and Energy Distributions.- 14. Construction and Structure of the S-Matrix.- 15. The Scattering of Signals by Diffraction Gratings.- References.

Method of forming diffraction gratings and optical branching filter elements produced thereby

Abstract: A method for making a diffraction grating utilizing a laser source, a beam splitter to split the light from the laser source into two light fluxes, a collimator to convert each light flux into a light flux which is parallel and enlarged in diameter, a mirror to irradiate each light flux on a substrate coated with a photoresist, and a photomask on the photoresist. The use of an intermediate mask and focusing leans enables the formation of a diffraction grating within a limited area. A blazed diffraction grating may be formed by splitting a laser beam into two beams having an increased beam radius, and irradiating a light-sensitive material with the resulting two beams to form an interference fringe. This method is characterized in that in a first exposure the two beams are incident on the light sensitive material through air to form an interference fringe having a clearance width of d, and in a second exposure, the two beams are irradiated on the light sensitive material through a symmetrical transparent member having an isosceles triangular cross section in such a manner that the origin coincides to form an interference fringe having a clearance width of d/2, and furthermore, in that the ratio of the first exposure energy to the second exposure energy is made equal to the ratio of the first term to the second term of a Fourier series obtained by expanding the periodical function of the waveform of the blazed diffraction grating.

Optical waveguide coupling device

Abstract: An optical waveguide coupling device which can perform switching functions by changing input light intensity, and associated method of construction thereof, in which the device comprises a base substrate etched to provide an optical grating having a predetermined grating period and amplitude. A thin metal film is deposited on the grating. Subsequently, a polymer film is deposited over the thin metal film, thus forming an optical waveguide. The field for the waveguide mode is nearly zero at the metal-polymer film interface, thus eliminating the loss of energy in the thin metal film. The metal film, in essence, reflects the input beam so that substantially no energy is lost via transmission through the thin metal film and thus all available energy is for coupling into the waveguide mode.

Preparation Of Planar Optical SiO 2 -TiO 2 And LiNbO 3 Waveguides With A Dip Coating Method And An Embossing Technique For Fabricating Grating Couplers And Channel Waveguides

Abstract: Planar monomode and multimode Si02-Ti02 waveguides were prepared with a dip coating method from Liquicoat solutions supplied by E. MERCK. By varying the Si02:Ti02 mixture ratio the value of the refractive index nF of the waveguiding films on Pyrex glass substrates can be chosen to lie between nF-1.6 and nF =1.36 First results on the preparation of LiNb03 waveguides are also presented. Thicknesses, refractive indices and losses of the waveguides were determined at the blue-green Ar laser wavelengths and at the He-Ne laser wavelengths λ=632.8 nm and λ=1.153 μm. With an embossing technique we fabricated surface relief gratings on Si02-Ti02 wave-guides. We used them successfully as input grating couplers. We propose to use this emboss-ing technique to fabricate channel waveguides and other integrated optical components in inorganic hard waveguiding materials such as Si02-Ti02.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Developments In Fabrication Of Binary Optical Elements

Abstract: We have produced highly efficient binary diffraction gratings -- 94% first order diffraction efficiency measured in the infrared (10.6 μm) on straight binary gratings and on binary holographic off-axis lenses. The observed point-spread functions of these lenses (F/10, f = 25 cm) were limited only by diffraction. To fabricate gratings we adapted IC production techniques. Our work brings together three independent developments: (1) theories on binary diffraction gratings operating in the EM domain, (2) large-scale integration (LSI) advances in pattern generation and substrate depositions, and (3) improvements in reactive ion-beam etching techniques.

Measurements of flow velocity in a microscopic region using a transmission grating

Abstract: This paper reports a method for measuring flow velocity in a microscopic region using a transmission grating. The flow velocity is determined from the measurement of moving particle images on a transmission grating placed in front of a photodetector. These images, formed by a microscopic objective, correspond to particles moving in a flow. The method is used to measure the spatial distributions of the flow velocity in small glass tubes and to compare some of the results with comparable data obtained with differential laser Doppler velocimetry. The resultant distributions are compared with the theoretical flow distributions obtained using the flow rates through the tubes. The results demonstrate that the transmission grating method is useful for measurements of the flow velocity in small probe volumes.

Apparatus for optically analyzing a sample

Abstract: An electro-optical system for rapid, accurate spectral analysis of the reflectivity or transmissivity of samples. A concave, holographic diffraction grating is oscillated at high speed to provide a rapid scanning of monochromatic light through a spectrum of wavelengths. The grating drive system is an electrically driven mechanical oscillator which utilizes the back EMF of the oscillator motor to maintain oscillation at the desired amplitude and frequency. A passive optical shutter mounted to the grating alternately blocks the light entering and exiting the monochrometer as the grating is oscillated. The resultant dark period is utilized by the system to provide a reference offset value and to control cooling of the detectors. A unique phase-locked loop circuit is employed to provide sample commands at precisely determined intervals to correctly correlate the spectral data with the output of the monochrometer. Source and exit optics are employed to optimally shape the light passing through the system. A unique detection head is provided to allow measurement of light transmission or reflectance with only slight modification of the system. An optical fiber is used to divert light from the beam at or near the sample. This light is electronically detected and the electronic detection signal is used to adjust the gain of the sample signal so as to compensate for atmospheric bands, temporal variations, and system response. This provides a true double (dual) beam operation.

Solar cell with two-dimensional reflecting diffraction grating

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 two-dimensional reflecting diffraction grating to internally reflect the incident light back into the active material.

Fiber optic bidirectional wavelength division multiplexer/demultiplexer with total and/or partial redundancy

Abstract: The wavelength division multiplexer/demultiplexer includes a gradient index of refraction (GRIN) lens and a diffraction grating located adjacent to one end of the GRIN lens. The diffraction grating is adapted for switching from a first angle to a second angle with respect to the GRIN lens. For both path and terminal equipment redundancy, first and second input optical fibers are located at first and second input locations on an end surface of the GRIN lens. A first and a second plurality of output optical fibers are also located on this end surface of the GRIN lens. The input and output optical fibers are located so that optical energy will travel from the first input optical fiber to the first plurality of output optical fibers when the diffraction grating is oriented at the first angle and optical energy will travel from the second input optical fiber to the second plurality of output optical fibers when the diffraction grating is oriented at the second angle.