Showing papers on "Diffraction grating published in 1988"

Diffraction of atoms by a transmission grating.

Abstract: We have demonstrated a novel diffraction grating for atoms. A collimated beam of sodium atoms with a de Broglie wavelength of 17 pm was diffracted by transmission through an array of slits with a spatial period of 0.2 \ensuremath{\mu}m formed in a gold membrane. This is the first reported diffraction of atoms by a fabricated periodic structure. Our transmission grating for atoms can divide or recombine an atomic beam coherently, and may provide the easiest route to the realization of an atom wave interferometer.

Coupled-Wave Analysis Of Two-Dimensional Dielectric Gratings

Abstract: Diffraction by two-dimensional surface-relief dielectric gratings are analyzed using rigorous three-dimensional vector coupled-wave approach. The method applies to arbitrary plane wave angle of incidence, wavelength, and polarization. In the resulting conical diffraction, the input TE and TM polarization are coupled and the diffracted orders are, in general, elliptically polarized. Diffraction characteristics of two-dimensional binary gratings are presented. Ultrahigh spatial-frequency gratings (grating period less light wavelength) are shown to exhibit polarization independent antireflection behavior (zero-reflectivity).

Multilayer diffraction grating

Abstract: This invention is for a reflection diffraction grating that functions at X-ray to VUV wavelengths and at normal angles of incidence. The novel grating is comprised of a laminar grating of period D with flat-topped grating bars. A multiplicity of layered synthetic microstructures, of period d and comprised of alternating flat layers of two different materials, are disposed on the tops of the grating bars of the laminar grating. In another embodiment of the grating, a second multiplicity of layered synthetic microstructures are also disposed on the flat faces, of the base of the grating, between the bars. D is in the approximate range from 3,000 to 50,000 Angstroms, but d is in the approximate range from 10 to 400 Angstroms. The laminar grating and the layered microstructures cooperatively interact to provide many novel and beneficial instrumentational advantages.

Ultra-high sensitivity accelerometers and gyroscopes using neutral atom matter-wave interferometry☆

Abstract: This paper shows that matter-wave interferometers employing low-velocity neutral atoms can be used as inertial sensors with sensitivities that exceed those of conventional mechanical sensors and multiple circuit optical interferometers by many powers of ten. The energy and mass dependence of the phase shifts that are due to rotation and acceleration are different. Thus a pair of interferometers with different energies and/or masses can perform simultaneous independent measurements of rotation and acceleration. A proposed configuration is one formed by a sequence of planar diffraction gratings operating in high order. Gratings consist of near-resonant standing-wave laser beams. Laser decelerated and cooled atomic beams provide a suitable source. Path curvature due to acceleration and rotation is canceled by magnetic field gradients that produce an effective magnetic levitation of the atoms in a feedback arrangement that maintains null phase shift.

Picosecond photorefractive and free-carrier transient energy transfer in GaAs at 1 mu m

Abstract: The strength, formation, and decay of photorefractive and free-carrier gratings written in GaAs by 43-ps pulses at a wavelength of 1 mu m are investigated using picosecond-time-resolved two-beam coupling, transient grating, and degenerate-four-wave-mixing techniques. Photorefractive weak-beam gains of a few percent are measured at fluences of a few pJ/ mu m/sup 2/ (0.1 mJ/cm/sup 2/), and gain from transient energy transfer is observed at fluences larger than approximately 10 mJ/cm/sup 2/ in the beam-coupling experiments. The roles of saturation and two-photon absorption in determining the final electron, hole, and ionized-donor populations and the roles of drift and diffusion in determining the quasi-steady-state photorefractive and free-carrier index modulations are discussed. >

Analysis of multilayered periodic structures using generalized scattering matrix theory

Abstract: The use of generalized scattering matrix theory is proposed as a fast, efficient approach for analyzing multilayer structures where in each layer is either a diffraction grating or a uniform dielectric slab, and all grating layers have the same periodicity. The overall scattering from the structure is determined by first evaluating a matrix of scattering parameters for each individual layer and then forming a scattering matrix for the entire structure by a procedure analogous to the cascading of networks in circuit theory. Higher-order spatial (Floquet) harmonics, including nonpropagating modes and cross-polarized fields, are taken into account as necessary. The approach is illustrated by computing the reflection coefficient of a multilayered resistive strip grating as a function of frequency. >

Matrix formalism for pulse compressors

Abstract: A matrix formalism for grating and prism compressors is introduced. It is an extension of the standard ABCD matrix formalism for Gaussian optics, but includes the possibility of considering dispersive elements such as gratings and prisms. The full formation on the frequency-dependent phase shift is obtained to compute the time delay dispersion. The formalism simplifies the design of compressors with focusing optics. Information on beam divergence and astigmatism is also acquired. >

Theory of transient energy transfer in gallium arsenide

Abstract: Numerical calculations are given for optical two-beam coupling in undoped, semi-insulating GaAs using picosecond pulses. Absorption at the intrinsic defect EL2, two-photon absorption, free-carrier absorption, photorefractive gratings, free-carrier gratings, and absorption gratings are included. Results for normalized probe transmission as a function of pump fluence and as a function of pump-probe delay show that the major effects are energy transfer from pump to probe or from probe to pump (depending on crystal orientation) due to the photorefractive effect, two-photon absorption, and free-carrier transient energy transfer from the pump to the probe. >

Light-induced erasure of self-organized chi((2)) gratings in optical fibers.

Abstract: Self-organized χ(2) gratings in optical fiber, prepared by irradiating the fiber with 1.06-μm light from a Q-switched mode-locked Nd:YAG laser simultaneously with its second harmonic, can be erased optically. This is accomplished by irradiating the prepared fiber with the 532-nm mode-locked Q-switched light alone, without the 1.06-μm light, or with intense green or blue light from an argon laser. The erasure is reversible, and the fiber can be reprepared as before for second-harmonic conversion. The nonexponential time dependence of the erasure process can be explained by a model involving charge separation during seeding and recombination during erasure.

Subpicosecond, widely tunable distributed feedback dye laser

Abstract: A simple, achromatic, widely tunable distributed feedback dye laser arrangement is described. It makes use of a microscope objective, which images a transmission grating into the active medium. With this arrangement subpicosecond operation and broad tunability (400–760 nm) is reported.

Stratified volume holographic optical elements.

Abstract: A computational algorithm for analyzing diffraction properties of optical devices, the optical beam propagation method, has suggested a new class of devices by which Bragg regime (thick grating) response can be obtained from a spaced sequence of thin grating layers. Such stratified volume holographic optical elements (SVHQE’s) can emulate distributed volume gratings in terms of diffraction efficiency and angular selectivity and in addition possess periodic diffraction properties that might serve, for example, as interconnections for optical cellular logic arrays. SVHOE’s also offer a unique capability for altering the device diffraction response on a layer-by-layer basis, allowing for control of both the diffraction peak width and the angular separation of adjacent peaks.

The effects of the truncation and curvature of periodic surfaces: a strip grating

Abstract: Equations are outlined for surfaces which are finite and curved in two dimensions (only locally periodic), as well as infinitely periodic in one dimension but truncated and curved in the second dimension. By removing the periodicity, a truncated strip-grating results and the scattered fields as well as an associated reflection coefficient are calculated. These numerically rigorous calculations are compared against two approximate solutions. The comparison is intended as a check of the approximate solutions toward their application, in particular, in the analysis of surfaces which are finite and curved in two dimensions. In general, the edge currents always differed from the currents induced on an infinite grating, while the interior strip currents on a finite grating (depending on the excitation wavelength) may or may not differ from those of an infinite grating. It is concluded that if a more accurate calculation of the spectral response is to be found, the interior currents must be better approximated. >

Grating enhancement of quantum well detector response

Abstract: We have measured the enhancement in the response of a quantum well infrared detector by the incorporation of a metallic diffraction grating into the structure. We find an enhancement ratio of about 30, and its spectrum indicates that waveguiding of diffracted light occurs within the sample. Strong coupling to evanescent modes of the grating is not observed.

Local normal mode analysis of guided mode interactions with waveguide gratings

Abstract: The reflection of a guided mode obliquely incident to a periodic, shallow, surface corrugation, waveguide grating is analyzed using the local normal mode expansion of coupled-mode theory. The coupling coefficients which give the strength of the TE-TE, TE-TM, TM-TE, and TM-TM mode interactions are evaluated as a function of incidence angle. The results are compared to the coupling coefficients obtained using a number of other analytical techniques. >

Arrangement for an integrated optical spectrometer and the method for manufacturing the spectrometer

Abstract: An arrangement for an integrated optical spectrometer having an optical film waveguide and a focusing optical grating with grating lines extending perpendicular to a plane of the film waveguide characterized by the grating having a fixed grating constant so that adjustment and contrast problems can be avoided. The new arrangement can take the form of a film waveguide in coaction with a ribbed waveguide disposed thereon, with the grating being formed in the edges of the ribbed waveguide.

Proposal for a new submicron dimension reference for an electron beam metrology system

Abstract: A new submicron level reference for an electron beam metrology system is proposed. This reference is a fine rectangular‐profile diffraction grating fabricated by laser interferometer lithography and anisotropic chemical etching of (110) crystalline silicon. The pitch size of the grating is derived from the wavelength of the laser and the angle of incidence of the holographic lithography. The optical diffraction measurement absolutely assures accurate grating pitch size. The measurement error is estimated to be smaller than 0.001 μm. A deep lamellar grating fabricated by anisotropic chemical etching of (110)Si generates a stable and high‐contrast secondary electron signal in an electron beam metrology system. Reference pitch size measurement by optical diffraction and by the electron beam metrology system assures that the pitch size error is smaller than 0.02 μm.

Dynamic optical interconnection device for integrated circuits

Abstract: An embodiment of the disclosed device includes: two coupled laser diodes, emitting a light wave which is modulated in frequency and amplitude by electrical signals which control the selection of one among several interconnections and represent a sequence of binary data also included is an optical guide embedded in the surface of a semiconductor substrate and a diffraction grating etched on the surface of the guide and substrate, coupled to the guide to diffract the light in several directions depending on the wavelength as well as photodiodes respectively located in one of the directions where the light can be diffracted, to give an electrical signal representing the binary data transmitted in the direction corresponding to the photodiode. In other embodiments, the photodiodes are coupled to laser diodes by means of a holographic grating.

Continuously rotating grating rapid-scan spectrophotometer

Abstract: An improved rapid-scan spectrophotometer with an optical grating continuously rotating at a constant angular velocity. An optical trigger actuated by the rotating turntable supporting the grating, actuates an analog to digital converter to sample at discrete times an output signal from the sample detector over the desired wavelength range and to store the digitized information in a direct memory access (DMA) buffer. The information may be retrieved as desired from the buffer for further processing or permanent data storage. With each revolution of the optical grating, the range (typically 15°) of wavelengths from the grating that provides useful information is sampled by the analog to digital converter and stored in the buffer. Because the grating is continuously rotating at a constant angular velocity and is not limited by the inertia of optical components, the spectrophotometer can be operated at a much higher scanning speed than an oscillating or vibrating grating spectrophotometer.

Optical record carrier scanning apparatus providing optoelectronic positioning of the scanning spot

Abstract: Optical record carrier scanning apparatus including a source of radiation which is tunable to produce different wavelengths of a radiation beam and an optical assembly for forming the radiation beam into a spot for scanning information tracks on the record carrier. The optical assembly includes a diffraction grating which diffracts the beam so that only a selected diffraction order sub-beam thereof is formed into the scanning spot, the diffraction angle of such sub-beam and consequently the position of the scanning spot relative to the track being scanned being variable by variation of the wavelength of the radiation beam. A periodic transverse variation of spot position can thus be produced entirely optoelectronically, for producing a tracking error signal to control the scanning spot to remain centered on the information track.

Dielectric grating induced by cavity standing wave as a new explanation of origin of nonlinear gain in semiconductor diode lasers

Abstract: The nonlinear gain due to induced index and gain grating caused by the cavity standing wave is analysed using coupled-mode equations. The grating coupling coefficient is calculated using the rate equation with an ambipolar diffusion term. The self-consistent solution of the coupling coefficient and the optical field indicate the existence of a nonlinear gain term with a surprisingly large magnitude. This gain nonlinearity is shown to contribute significantly to the modulation damping factor of semiconductor diode lasers.

Measurement of the diffusion-length of carriers and excitons in CdS using laser-induced transient gratings

Abstract: Using a laser-induced grating arrangement we measure the probe beam diffraction intensity under stationary excitation conditions as function of the grating constant. We developed a mathematical model and extract by comparison with experimental data the diffusion lengths of the quasiparticles existing at various temperatures and excitation levels in the CdS sample from the experimental findings.

Focusing grating couplers for polarization detection

Abstract: A new polarization detection method using focusing grating couplers was proposed and demonstrated. Mode dispersion of a waveguide and high selectivity of the coupling condition of the grating is utilized for detecting the polarization state of a beam in the air. The crosstalk depends on the grating aperture and the index difference between TE and TM modes in the waveguide. A high performance device was designed and fabricated, and the function was experimentally confirmed by using a laser diode of 0.83 mu m wavelength. >

Nonlinear optical processes in a polymer waveguide: Grating coupler measurements of electronic and thermal nonlinearities

Abstract: We report here the first clear demonstration of intensity‐dependent phase shift due to electronic nonlinearity in a nonlinear polymer waveguide in which propagation distances over 5 cm have been achieved with total attenuation of ∼1.2 cm−1 . Intensity‐dependent coupling angle, intensity‐dependent coupling efficiency, and limiter action behavior have been observed in the polyamic acid waveguide using grating excitation with 400 fs, 80 ps, and 10 ns pulses. A nonlinear grating coupler analysis identifies the subpicosecond and picosecond processes with electronic nonlinearity, but the dominant effect in the nanosecond experiment is due to thermal nonlinearity derived from weak absorptions. The magnitude and sign of n2 of electronic nonlinearity are measured.

Phase correction of femtosecond optical pulses using a combination of prisms and gratings.

Abstract: The performance of a combination of prisms and diffraction gratings as phase correctors is calculated numerically. Special attention is given to the regime where the pulse duration is 10 fsec or less.

Antireflection gold surface-relief gratings: experimental characteristics

Abstract: A systematic procedure using the effective index method and impedance matching has recently been developed Appl. Opt.26, 3123 ( 1987)] for the design of antireflection high-spatial-frequency rectangular-groove gratings on lossy materials including high conductivity metals. The design procedure in turn can be used as a starting point to design antireflection metallic gratings with lower spatial frequencies using rigorous coupled-wave analysis. These lower spatial-frequency gratings have the advantage of being easier to fabricate. In the present work, a particular antireflection gold grating design (having a period of 1.0 μm, a filling factor of 50%, and a groove depth of 147.5 nm for use at a freespace wavelength of 500 nm, normal incidence, and polarization parallel to the grooves) was fabricated and its diffraction characteristics experimentally measured. The grating indeed showed very nearly zero specular reflection in the blue region of the spectrum. Unlike previously reported antireflection anomalies, the effect is broadband occurring over a broad range of wavelengths and angles of incidence, and for both orthogonal polarizations. This work clearly shows that the systematic design of zero specular reflection grating surfaces is possible.

Head-up display device

Abstract: PURPOSE: To obtain the head-up display device which forms no unnecessary image or eliminates the incidence of an unnecessary image on the eyes of an observer even when a display element which has a spread of luminous flux to some extent as a display element is used, and enables the display information of the display element and image information to excellently be observed. CONSTITUTION: The luminous flux from the display element 101 is reflected and diffracted by a 1st diffraction grating 102 and a 2nd diffraction grating 104 toward the observer, and the image information 109 behind the 2nd diffraction grating 104 and the display information of the display element are spatially superimposed and observed in the same visual field through the 2nd diffraction grating. In this case, a louver 103 which passes only diffracted light of specific degree from the 1st diffraction grating is arranged between the 1st diffraction grating and 2nd diffraction grating. COPYRIGHT: (C)1992,JPO&Japio

Time-resolved buildup of a photorefractive grating induced in Bi(12)SiO(20) by picosecond light pulses.

Abstract: Photorefractive gratings are induced with picosecond light pulses in a BSO crystal. Both experiment and calculations show a buildup of the effect governed by a diffusion of the excited charge carriers that occurs after illumination.

Pulses of Four Optical Cycles from an Optimized Optical Fibre/Grating Pair/Soliton Pulse Compressor at 1·32 μm

Abstract: In this Letter, we report on the generation of pulses as short as 18 fs by means of an optimized two-stage optical fibre-grating pair and high-order soliton-effect pulse compressor. These are the shortest pulses yet reported in the near-infrared spectral region and correspond to four optical cycles at 1·32 μm.

Optical pickup apparatus and optical grating assembly therefor

Abstract: An optical pickup apparatus for optically reading the data stored in a flat information carrier disc in the form of tiny pits. The pickup apparatus directs a beam of light from a light source to the disc surface. The impinging beam is modulated by the data pits and reflected back to a photodetector. A novel optical grating assembly is disposed between the light source and the information disc, and includes a diffraction grating for the light beam from the source and a holographic grating for directing part of the light beam reflected by the disc to the photodetector. The diffraction and holographic gratings are formed integral with each other into the grating assembly.