Showing papers on "Diffraction efficiency published in 1984"

Polarization holography. 1: A new high-efficiency organic material with reversible photoinduced birefringence.

Abstract: A new organic material for polarization holographic recording--azo-dye methyl-orange, introduced in polyvinyl alcohol (PVA)--is fabricated and investigated. It possesses all the good characteristics of the known polarization-sensitive materials--high sensitivity, reversibility, etc.--but excels them substantially in the magnitude of the photoinduced birefringence: delta n > 10(-3). This makes possible the recording of reversible polarization gratings with diffraction efficiency over 30%. Depending on the conditions of production and subsequent mechanical and thermal treatments the layers of methyl orange/PVA may also have intrinsic birefringence. In this paper the results of experimental investigations into the properties of this new material are reported.

Diffraction Efficiency and Selectivity of Polarization Holographic Recording

Abstract: Polarization holographic recording, based on photoinducing optical anisotropy in the recording material, is examined. The properties (diffraction efficiency and selectivity) are discussed for two t...

Polarization holography. 2: Polarization holographic gratings in photoanisotropic materials with and without intrinsic birefringence.

Abstract: Results are reported of experimental investigations on the diffraction efficiency and its polarization dependence of holographic phase polarization gratings in a photoanisotropic medium methyl orange/PVA with intrinsic birefringence. A comparative study of layers with different intrinsic birefringence was conducted. The conditions—initial birefringence and a type of polarization recording—were found to have high diffraction efficiency (>30%) and strong dependence on the direction of polarization of the linearly polarized readout beam. The results are in agreement with the theoretical considerations on such gratings.

I Rigorous Vector Theories of Diffraction Gratings

Abstract: Publisher Summary This chapter describes the rigorous vector theories of diffraction gratings. The diffraction grating is a valuable instrument for scientific research. It is mainly used for spectroscopy and filtering. Even though the holographic grating has not eliminated the classical, ruled grating, which remains the most suitable for important applications, it has permitted a considerable extension of the use of gratings for industrial or scientific purposes such as wavelength selectors for tunable lasers, selective surfaces for solar energy, masks for photolithography, beam sampling mirrors for high power lasers, spectrometers in extreme ultraviolet (UV) or x-ray regions for Space Optics. In addition, one can consider that rigorous vector theories of gratings are able to solve almost all the classical problems of gratings encountered by manufacturers and users.

Multichannel phase-shifted interferometer

Abstract: A new real-time interferometer based on diffraction phenomena is discussed. It consists of a point-diffraction interferometer fabricated on a transmission grating. The real-time data-analysis capability is achieved by simultaneously introducing a phase shift (piston) on the three separate channels of diffracted interferograms. Mathematical analysis and preliminary observational results are included.

Reflection-hologram processing for high efficiency in silver-halide emulsions

Abstract: The results are described of experiments carried out to develop improved processing methods for reflection holograms in bleached silver halide emulsions, as a result of which overall efficiencies of nearly 66% (75% after allowing for specular reflections) have been achieved for gratings recorded by two plane waves at 514.5 nm in an index-matching tank. These figures are limited almost solely by scatter and may approach the limits obtainable with the recording material, Agfa 8E56HD. Close agreement has been reached between experimental measurements of the off-Bragg response of the gratings and theoretical predictions based on coupled-wave analyses, allowing determination of the principal grating parameters and revealing maximum efficiency to correspond to a permittivity modulation of ~8.7%.

Diffraction characteristics of photoresist surface-relief gratings

Abstract: Theoretical results from rigorous coupled-wave analysis are compared with experimental diffraction characteristics for holographically formed dielectric photoresist surface-relief gratings with deep grooves (greater than a grating period) and high diffraction efficiency (>85%). The angular selectivity (at a fixed wavelength) and the wavelength selectivity (at a fixed angle of incidence) are presented for both TE and TM incident polarizations. Modeling the gratings as a surface-relief modulated half-space and using rigorous coupled-wave analysis are shown to produce good general agreement with the experimentally measured diffraction characteristics.

Dielectric surface-relief gratings with high diffraction efficiency

Abstract: Diffraction properties of dielectric surface-relief gratings were investigated by solving Maxwell’s equations numerically using the differential method. The diffraction efficiency of a grating with a groove depth about twice as deep as the grating period is comparable with the efficiency of a volume phase grating. Dielectric surface-relief gratings interferometrically recorded in photoresist can possess a high diffraction efficiency of up to 94% (throughput efficiency 85%). Calculated results were also found in good agreement with the experimental data.

Holographic scanner control based on monitored diffraction efficiency

Abstract: Operating parameters for a multiple facet holographic disc scanner are adjusted on real time basis as a function of the actual diffraction efficiency of the facet region aligned with the impinging laser beam. The operating parameters are adjusted to achieve optimum signal levels independent of facet characteristics. Diffraction efficiency is inversely related to zero order beam power for a given level of input beam power. A photodetector measures the zero order beam power. The output of this photodetector is used to control video amplifier gain and/or semiconductor laser current.

Diffraction Efficiency and Angular Selectivity of Volume Phase Holograms Recorded in Photorefractive Materials

Abstract: The recording and replay of volume phase gratings in photorefractive crystals is investigated for both transmission and reflection geometries. Differential equations are derived and solved for a range of parameters including the length of the crystal, the magnitude, spatial distribution and phase angle of the refractive index modulation, the beam ratio at recording, and the angular range at replay. The recording process is assumed to reach a steady-state limit before replay with a weak probe beam. Solution of the repaly equations is mainly by numerical integration, although analytic solutions are derived for special cases. It is found that in certain cases the diffraction efficiency can be greatly increased by replaying the hologram at an angle different from the recording angle.

Layered synthetic microstructure technology considerations for the extreme ultraviolet

Abstract: It is demonstrated that layered synthetic microstructures (LSMs) can provide mirrors with enhanced normal incidence reflectance in the 300-A spectral region Experimental results are presented for Pt-Si and Ir-Si structures fabricated by electron-beam deposition at pressures of about 10 to the -6th Torr, and it is shown that the enhancement is realized over a limited bandwidth of 75 A One potential application of LSMs is their use as coatings on diffraction gratings to enhance normal incidence reflection efficiencies Preliminary results for the Ir-Si combination on a diffraction grating show that LSMs enhance grating efficiencies in the EUV by a factor of about 3

Optical self-alignment system

Abstract: An optical self-alignment system comprises a laser source (12). a substrate (A) with a first diffraction grating for receiving laser beams (L) from the laser source (12), a substrate (B) with a second diffraction grating disposed within Fresnel zone of the first diffraction grating (A), and a photoelectric detector (C) for detecting Fraunhofer diffraction ray of Oth order by the second diffraction grating (B). In order to adjust the relative position between the two substrates (A,B) in orthogonal directions to the laser beams (L) at high accuracy, the first (A) and second (B) diffraction gratings are provided with two groups of combined diffraction gratings so that phase difference of 180° is produced in the Moire signals, maximum displacement point of Moire signal is detected with respect to relative position displacement of the diffraction gratings, and the substrates (A,B) are positioned at maximum intensity displacement of two groups of the Moire signals.

Extreme UV measurements of a varied line-space Hitachi reflection grating: efficiency and scattering.

Abstract: The first extreme UV measurements of a grating mechanically ruled with smooth variations in the grating constant are presented. The grating characteristics are summarized and a schematic of the testing apparatus is shown and described. The procedure for obtaining the absolute grating efficiency is given. The results for that efficiency as a function of wavelengths of 68, 170, 256, 304, 584, and 1216 A are reported and discussed. Efficiency measurements were also made as a function of position across the ruled width at 256 A and 87 deg incident angle, and the results are discussed. Scattering measurements performed via computer acquisition of diffracted image profiles are reported.

Fringe formation in incoherent light with a two-grating interferometer

Abstract: A higher-order analysis is made for the formation of point-source and extended-source polychromatic fringes in a two-grating interferometer. Various conclusions result. For best fringes, a polychromatic point source should be on-axis, and the second grating should be twice the spatial frequency of the first.

Flat-field linearized scans with reflection dichromated gelatin holographic gratings.

Abstract: A polygonal holographic scanner that combines a reflection volume hologram on dichromated gelatin with a computer-generated hologram (CGH) is described. Such a scanning system allows for a compact folded version and highly efficient Bragg diffraction into a single order. A design of the scanner with a nonspherical wave front based on ray tracing and the damped least-squares optimization technique allows a flat-field linearized scan to be used. A suitable trade-off between field flatness and position linearity of scan is adopted. The optimized wave front designated by polynomials is encoded into a CGH. Experiments demonstrating the feasibility of this scannner are presented. Additional data on the diffraction efficiency and the spectrally diffracted intensity of the reflection volume gratings are also shown.

A coherent photoacoustic approach to excited-state-excited-state absorption spectroscopy: application to the investigation of a near-resonant contribution to ultrasonic diffraction

Abstract: The previously reported coherent photoacoustic method for measuring weak absorptions is extended to excited-state-excited-state spectroscopy for which conventional acoustic and thermal lensing techniques are greatly reduced in sensitivity. The method involves a picosecond pulse sequence with four pulses. The first pulse populates the excited state. Then, a pair of time coincident pulses cross in the sample, making an optical interference pattern and generating an acoustic diffraction grating. The amplitude of the acoustic grating is proportional to the excited-state-excited-state absorption cross section. The amplitude is measured by the Bragg diffraction of the fourth pulse from the acoustic grating. This method can be readily applied to liquids, glasses, or crystals. Excited-state absorption at 532 nm by the SI state of pentacene in p-terphenyl host crystals is examined at room temperature and 1.4 K. The results are used in addressing the mechanism for acoustic diffraction of a probe beam nearly resonant with a strong and narrow ground-state transition, e.g., pentacene in p-terphenyl at 1.4 K. It is demonstrated that there is a density wave induced spectral shift contribution to the acoustic grating which results in greatly increased diffraction efficiency near resonance.

Optical-gyroscope application of efficient crossed-channel acoustooptic devices

Abstract: An acoustooptic (AO) deflector/modulator using a single-mode crossed-channel waveguide of 2Δn type and an interdigital transducer is fabricated in aY-Z LiNbO3 substrate. This module has shown a high diffraction efficiency. A 50% diffraction efficiency and a bandwidth of 13.4 MHz were obtained with 0.13 W of surface-acoustic wave power centered at 320MHz. Since the cross section of the channel waveguide and that of the optical fiber are comparable, the interfacting of the resultant acoustooptic devices with fiber optical systems would greatly simplified. In addition, the frequency-shifted optical beam can be conveniently used as a reference signal or local oscillator in heterodyne detection. Consequently, this cross-channel acoustooptic device should find a variety of applications in realizing an integrated-optics module with a 50–50% power slit, optical communication, and an optical fiber system. One of those applications, optical gyroscopes, is proposed by using this kind of crossed-channel AO device.

Cell-oriented on-axis computer-generated holograms for use in the Fresnel diffraction mode.

Abstract: A type of computer-generated hologram (CGH) is introduced which works in the Fresnel diffraction mode and generates the desired wave front on-axis. Such holograms rely on the use of the detour-phase method suitably modified for Fresnel diffraction and on the sampling theorem; therefore, they are of the cell-oriented type. The concept of a carrier or reference wave is not needed to introduce them; the Huygens-Fresnel principle provides a complete description of their diffracted waves. Consequently, no orders in the usual sense of grating orders or zone plates or natural holograms can be defined. Only orders in the sense of the sampling theorem exist for these computer-generated holograms, and the useful order is the central one; it is also the brightest and does not overlap with other orders. These questions are discussed and illustrated by experimental examples in connection with the problem of diffraction efficiency. Among the examples, the CGH of a single point on-axis is considered; it is in general not a zone plate.

Perfectly blazed triangular groove reflection gratings

Abstract: An experimental and numerical verification of profiles predicted by Cheo et al. [ J. Opt. Soc. Am.67, 1686 ( 1977)] for simultaneous TE- and TM-blazed triangular groove gratings is given. Corrected values also presented. The experimental results at 35 GHz show an n = −1 order diffraction efficiency as high as 99.9% for both polarizations. The numerical results for scattering by a perfectly conducting strip with six corrugations show a diffraction efficiency of about 97%.

Effect of Temperature on Diffraction Efficiency of Holograms Recorded in Arsenic Trisulphide Thin Films

Abstract: Hologram recording in arsenic trisulphide thin films of thickness 300 nm, prepared by electron beam evaporation on substrates between room temperature and 150°C, have been investigated experimentally. These holograms were evaluated for the diffraction efficiency (DE) and resolution. The results were compared with published results for As2 S3 films prepared in gelatin. The DE was investigated for beam ratios of 1, 5 and 10, and was found to decrease for increasing temperature and beam ratio. Thus decrease in DE at an elevated substrate temperature (150°C) is attributed to microstructural changes taking place in the As2 S3 films.

Design and fabrication of efficient diffraction transmission gratings on step-index optical waveguides.

Abstract: High-efficiency and low loss constant periodicity gratings have been fabricated and evaluated on single-mode planar optical wave guides. The most important parameters that will affect the lens performance are the coupling coefficient and the Q (or ρ) factor. The coupling coefficient has been found to be given by Kc = Δneff/(λ0/2). Investigation of the Δneff value has shown that for small groove heights larger Δneff can be obtained for CeO2 deposited grooves than for etched grooves. In grating structures where Q and ρ factors are high, the effect of the higher orders of diffraction is negligible, and there is a good agreement between the experimentally measured characteristics and the prediction from the coupled mode theory. However, minor variations in the fabrication processes (e.g., Δn ≃ 0.02) may cause the diffraction efficiency to vary as much as 15%, while the angular field of view does not seem to be affected by process variations.

Transient holograms in dyed plastic.

Abstract: A low-cost and readily available holographic material (dyed Plexiglas) has been studied. Green light from an argon laser was used to form an interference pattern which was recorded by the red plastic. Simultaneously red light was sent and diffracted by the recorded structure. Curves showing the diffraction efficiency, as a function of exposure and maximum diffraction efficiency as a function of the grating frequency are presented. Applications in single- and double-exposure holography have been made.

Construction Of Diffractive Optical Elements In Non-Coherent Light

Abstract: Methods are described for producing optical elements, such as grating and lenses, in light of reduced temporal or spatial coherence. The preferred interferometer for producing fringes in light of low coherence is one formed from diffraction gratings. Considerable more noise reduction is achieved.

Diffraction gratings and optical aberrations.

Abstract: The effects introduced by a plane diffraction grating on the diffracted wave front when a quasi-plane beam incides on it are calculated. Effects not previously discussed appear.

Construction and evaluation of HOEs made in light of reduced coherence.

Abstract: Using interferometers adjusted for extended source operation, it is shown that holographic optical elements (HOEs) can be constructed with any designed conjugate focal planes. Noise and diffraction efficiency measurements show that the reduced coherence method can yield HOEs of high diffraction efficiency and good SNR.

Acousto-Optic Bragg Cells For Ew Applications

Abstract: The design of acousto-optic Bragg cells for EW application is discussed. The critical issues of concern include operating wavelength, bandwidth, resolution, efficiency, optical scatter, intermodulation products and maximum power handling capability. Experimental results obtained at 0.83 micrometer have demonstrated a bandwidth of 1.8 GHz with a diffraction efficiency of about 6 percent per RF watt.

Influence of the characteristic curve of the material on the diffraction efficiency of holographic volume phase gratings

Abstract: The behaviour of the diffraction efficiency of holographic gratings is discussed on the basis of the multiwave coupled-wave approach, taking into consideration the photoinduced change in the refractive index of the recording medium. The cases of Bragg and off-Bragg reconstruction in Bragg and mixed diffraction are considered. The influence of the higher harmonics of the refractive index modulation profile on the diffraction efficiency is shown.

Transient orientational grating technique for investigations of fast molecular relaxation processes

Abstract: A theoretical description of a three-pulse transient grating technique is given where the pump pulses form orientational gratings. Including energy relaxation and angular reorientation the temporal behavior of the diffraction efficiency and energy transmission is discussed with respect to the dependence on the corresponding rate constants and the results are compared with experimental data for Rh6G and RhB. The polarization plane of the pulse diffracted by the grating is found to be rotated in dependence on its initial polarization.