Showing papers on "Diffraction efficiency published in 1985"
TL;DR: In this paper, the zero-eth order diffraction efficiency of a three-layer dielectric grating is studied theoretically and experimentally, and the operation of the structure as a tunable narrow-band wavelength filter in a reflection regime is demonstrated.
242 citations
TL;DR: In this paper, LiNbO3 has been shown to have a high photoconductivity, which is related to a distinctive electronic environment for impurities in the damage-resistant crystals.
Abstract: Compositions of lithium niobate containing 4.5 at.% or more MgO have the ability to transmit, without distortion, light 100 times as intense as undopecl compositions. Holographic diffraction measurements of photorefraction have demonstrated that the improved performance is due to a hundredfold increase in the photoconductivity, rather than to a decrease in the Glass current. The damage-resistant compositions are also distinguished by a thermal activation energy of 0.1 eV for the diffraction efficiency, an OH-stretch vibration at 2.83 Am, a lattice phonon absorption at 21.2 Am, an electron spin resonance signal for Fe impurities at 1500 G, and, after reduction by heating in a vacuum, an optical absorption band at 1.2 um. (The corresponding values for undopedl LiNbO3 are 0.5 eV, 2.87 um, 21.8 um, 790 G, and 0.5 um, respectively.) The high photoconductivity is thus related to a distinctive electronic environment for impurities in the damage-resistant crystals. The photoconductivity strongly affects the impedance and time constants of signal processing devices made of LiNbO3.
104 citations
TL;DR: In this article, the authors studied the mechanism and the dynamics of degenerate four-wave mixing in a nematic liquid crystal film, where nanosecond laser pulses are used to generate an index grating associated with the changes in the density and in the order parameter.
Abstract: We have studied the mechanism and the dynamics of degenerate four-wave mixing in a nematic liquid crystal film. Nanosecond laser pulses are used to generate an index grating associated with the changes in the density and in the order parameter. We have measured and analyzed the contributions from these two mechanisms, their interference effects rise and decay time constants, and have also performed a detailed analysis of the diffraction efficiency. This study quantitatively characterizes the potential usefulness of nematie films for four-wave mixing based applications.
95 citations
TL;DR: A theoretical optimization of echelette gratings on silicon substrate allows the practical construction of wavelength demultiplexers for optical communications in the 0.78–0.9 and 1.35-μm ranges to be obtained.
Abstract: Echlette gratings made by chemical etching of silicon substrates have already proved to be efficient, easy to implement, and well adapted to optical wavelength demultiplexing [ Y. Fujii K. I. Aoyama J. I. Minowa , “ Optical Demultiplexer Using a Silicon Echelette Grating,” IEEE J. Quantum Electron.QE-16, 165 ( 1980).]. This paper describes a collaboration between experimentalists and theoreticians devoted to the practical construction of wavelength demultiplexers for optical communications in the 0.78–0.9 and 1.2–1.35-μm ranges. A theoretical optimization of echelette gratings on silicon substrate allows us to obtain a very high diffraction efficiency. The experimental results confirmed the theoretical predictions.
86 citations
TL;DR: In certain conditions, the diffraction efficiency is shown to be exactly proportional to the inverse of the object beam intensity, and the dependence of the range of beam ratios over which inversion occurs on the experimental parameters of total writing beam intensity and applied electric field is investigated.
Abstract: In this paper, we consider a two-wave mixing system using a photorefractive medium and compute the diffraction efficiency as a function of the writing beam ratios. In certain conditions, the diffraction efficiency is shown to be exactly proportional to the inverse of the object beam intensity. Experimental results, obtained using a Bi12GeO20 crystal, are compared to the theoretical expression. In particular, we investigate the dependence of the range of beam ratios over which inversion occurs on the experimental parameters of total writing beam intensity and applied electric field. Results of performing inversion of gray-scale objects using a degenerate four-wave mixing setup are shown.
46 citations
TL;DR: In this paper, a maskless technique for producing diffraction gratings has been proposed for the fabrication of distributed feedback laser which are currently made by a multistep photoresist process.
Abstract: Direct photoelectrochemical (PEC) etching of diffraction gratings on n‐InP and n‐GaInAsP in a 2‐M HF/0.5‐M KOH solution has been demonstrated using laser interference holography. Development of a maskless technique for producing gratings has potential application in the fabrication of distributed feedback lasers which are currently made by a multistep photoresist process. Submicron diffraction gratings having a period of 0.5 μm, corresponding to second‐order feedback in GaInAsP at λ=1.55 μm, have been achieved. Measurements were obtained on the exposure characteristics, diffraction efficiency, and PEC etching sensitivity of gratings produced in InP and GaInAsP as a function of the writing beam intensity, laser wavelength, material doping level, and grating spatial frequency. For grating frequencies greater than 100 mm−1 the sensitivity was observed to decrease approximately as the inverse square of the spatial frequency. In addition, undoped InP and GaInAsP exhibited significantly lower sensitivities than...
45 citations
TL;DR: In this article, an f/5 binary lens with a diffraction efficiency of 96% at 10.6 um was constructed from two binary gratings with a 2 in. entrance aperture and a magnification of 5.6 mm.
Abstract: By combining advances in lithography and electromagnetic grating theory, we recently have demonstrated the ability to produce highly efficient binary gratings and binary lenses for use at 10.6 um. Electromagnetic theory predicts that binary gratings with the proper parameters can achieve a first-order diffraction efficiency of nearly 100%. If the periodicity of the grating is on the order of the radiation wavelength, all of the orders become evanescent except for the zero and positive first orders. By choosing the depth-to-period ratio and duty cycle properly, the zero order can be suppressed, placing virtually all of the incident radiation into the first diffracted order. Theoretical calculations have been done only for constant period gratings. However, assuming a lens pattern to be a minor perturbation of a grating, we succeeded in producing an f/5 binary lens with a diffraction efficiency of 96% at 10.6 um. Furthermore, because of the high efficiency of these elements, it becomes practical to consider using more than a single diffractive element in a system. We have constructed a simple afocal telescope from two binary lenses. The telescope has a 2 in. entrance aperture and a magnification of 5. A final point to be considered is the wavefront quality of these elements. Electron beam machines, which are used to write the lens patterns, are designed to draw the pattern in a raster fashion. This quantization sets a limit on the quality of the lens pattern.
41 citations
TL;DR: It is found that three- element cascades can exhibit spectral and field angle bandwidths essentially as broad as two-element cascades and that these bandwidths are in excess of 2300 A and 7° respectively.
Abstract: A comprehensive treatment is presented for the diffraction efficiencies of transmission holographic elements and cascade lenses when subject to broad spectral and field angle detunings. Experimental measurements are made in support of our theory on holographic optical elements fabricated in bleached silver-halide emulsions and in dichromated gelatin. The theory of holographic grating diffraction efficiency is studied through two approaches. A numerical treatment based on the theory of thin grating decomposition is implemented and shown to be in close agreement with other theories. Additionally, a more approximate approach is pursued in which the volume grating is treated as a phased array of scatterers. The latter approach leads to closed-form formulas in addition to a simple physical picture of volume effects. It is found that three-element cascades can exhibit spectral and field angle bandwidths essentially as broad as two-element cascades and that these bandwidths are in excess of 2300 A and 7° respectively.
37 citations
TL;DR: Two-photon absorption from crossed Gaussian laser beams creates a volume grating containing both a primary and a second-order sinusoidal index modulation.
Abstract: Two-photon absorption from crossed Gaussian laser beams creates a volume grating containing both a primary and a second-order sinusoidal index modulation. Unlike with linear excitation, the two-photon-induced grating exhibits two Bragg diffraction peaks having different decay rates. Comparison of diffracted orders from volume gratings allows the order of the excitation process to be determined.
34 citations
TL;DR: Combining holographic and femtosecond laser pulse compression technology, gigawatt peak power and 85-fsec bandwidth-limited laser pulses were obtained.
Abstract: Combining holographic and femtosecond laser pulse compression technology, gigawatt peak power and 85-fsec bandwidth-limited laser pulses were obtained. Pulse compression was achieved using a pair of high diffraction efficiency volume phase transmission holographic gratings.
22 citations
TL;DR: In this article, the efficiency of an echelle grating spectrometer incorporating prism cross-dispersion is empirically evaluated over a broad wavelength range incorporating a large number of orders.
Abstract: The efficiency of an echelle grating spectrometer incorporating prism cross-dispersion is empirically evaluated over a broad wavelength range incorporating a large number of orders. A derived parameter, the spectrometer efficiency, proportional to the spectrometer luminosity, conveniently gauges dynamic features of the echelle efficiency. Characteristics of efficiency over broad wavelengths suggested by earlier work are clearly observed. The shift of blaze wavelength with decreasing order of diffraction, predicted in a recent model of echelle grating efficiency, is experimentally documented.
TL;DR: A mixture of malachite green and ammonium dichromate has been used to photosensitize gelatin films and the results showed that the spatial frequency of the resultant phase grating was twice the one presented when α = 0°.
Abstract: A mixture of malachite green and ammonium dichromate has been used to photosensitize gelatin films. When this material is irradiated with polarized light an anisotropy is induced with its optical axis parallel to the electric vector of the incident vibration. After proper development of the material, the parts that showed anisotropy present a change in the refractive index of the gelatin independent of the orientation of the optical axis of the exposed part. On this basis the recording material was used to record interference gratings. When the two coherent recording beams had an angle α = 90° between their relative polarizations, the spatial frequency of the resultant phase grating was twice the one presented when α = 0°.
TL;DR: In this article, the process of holographic recording and a reconstruction of spatial and temporal characteristics of an optical field was investigated and it was shown theoretically and experimentally that this can be achieved by recording spectral amplitude-phase holograms in spectrally selective light-sensitive materials capable of storing harmonic components of the reference and object waves.
Abstract: An investigation is made of the process of holographic recording and a reconstruction of spatial and temporal characteristics of an optical field. It is shown theoretically and experimentally that this can be achieved by recording spectral amplitude–phase holograms in spectrally selective light-sensitive materials capable of storing harmonic components of the reference and object waves. A report is given of experiments on low-temperature solid solutions of large organic molecules in which stable narrow dips in the impurity absorption spectrum can be "burnt out" by photochemical reactions. The causality principle operating via the phase part of a hologram results in selection of one of the images: either a virtual image with a direct time dependence or a real image with a reversed time dependence. An experimental check of the properties of spacetime holograms yielded a fairly high (for practical applications) diffraction efficiency of ~50%.
TL;DR: In this article, a numerical analysis of thin corrugated conducting strips with rectangular-groove profiles dual blazed to the n = −1 spectral order is presented, showing that high-efficiency gratings remain efficient as the number of grating elements is reduced to as few as two, provided that incidence is not near grazing.
Abstract: A numerical analysis of thin corrugated conducting strips with rectangular-groove profiles dual blazed to the n = −1 spectral order shows that high-efficiency gratings remain efficient as the number of grating elements is reduced to as few as two, provided that incidence is not near grazing. Numerical results show that the main effect of reduced grating size is a broadening of the diffracted beam, which can be predicted from a simple formula. For TM polarization a single corrugation diffracts correctly, but current singularities at the ends prevent this for TE polarization. The results are shown to apply also to gratings of the same surface profile but with flat bottoms of finite thickness.
TL;DR: EPR experiments show that the speed of photoreduction of chromium ions is changed by electron donors and by baking, which affects the position of the diffraction efficiency spectral maximum as well.
Abstract: Holographic parameters of dichromated gelatin layers are improved by introducing electron donors such as N-N′ dimethylformamide into the layers. Simple reflection holograms are recorded. Their diffraction efficiency is greater compared with that of standard dichromated gelatin holograms. Recording at 6 mJ/cm2 (λ = 488 nm) gives a diffraction efficiency of ∼40%. The presence of electron donors does not deteriorate the hologram SNR. Heat treatment of recorded but undeveloped holograms leads to higher holographic sensitivity. EPR experiments show that the speed of photoreduction of chromium ions is changed by electron donors and by baking. This is confirmed by refractive-index and gelatin-melting-point temperature measurements. Baking affects the position of the diffraction efficiency spectral maximum as well.
TL;DR: In this article, the phase shift and efficiency of perfectly conductor wire gratings were analyzed for several diffraction orders, for four shapes of cross-section, and for both fundamental cases of polarization.
Abstract: Using the Hamiltonian method that we have recently proposed [1, 2] and which is described in the IEEE transactions on antennas and propagation [3], we give some theoretical data related to perfectly conductor wire gratings Phase-shift and efficiency are given for several diffraction orders, for four shapes of cross-section, and for both fundamental cases of polarization
TL;DR: In this paper, a computer generated off-axis binary lens with first-order diffraction efficiency of 94% was produced using straight-line binary diffraction gratings operating in the electromagnetic domain.
TL;DR: In this article, the role of symmetry of the profile of a diffraction grating on its reflectivity at normal incidence has been investigated and it was shown that the peaks are caused by the vanishing of certain Fourier components of profile function.
Abstract: We present a series of numerical calculations which illustrate the role of symmetry of the profile of a diffraction grating on its reflectivity at normal incidence. Here one finds reflectivity dips (or peaks) produced by grating-induced coupling of the incident photon to surface polaritons. When the grating profile has either even or odd parity, we find one of the two reflectivity dips expected at normal incidence is absent, in agreement with recent data. In addition, we find that the peaks are caused by the vanishing of certain Fourier components of the profile function. This result agrees with analogous results obtained in the theory of atom-surface scattering.
TL;DR: The diffraction properties of bleached reflection holograms are studied at different replay wavelengths to determine the wavelength dependence of the average refractive index, the average absorption, and the refractive-index modulation of the hologram.
Abstract: The diffraction properties of bleached reflection holograms, recorded by two plane waves in Agfa 8E56 photographic emulsion, are studied at different replay wavelengths. Measurements of the transmitted beam intensity against the replay angle of incidence are compared with a theoretical model to determine the wavelength dependence of the average refractive index, the average absorption, and the refractive-index modulation of the hologram.
TL;DR: In this article, Bragg diffraction from volume thermal gratings excited by crossed Gaussian laser beams provides a sensitive measurement of one and two-photon absorption in fluid solution, and the minimum detectable onephoton absorptivity (base e) was αmin = 1.0 × 10−6 cm−1 in a 3.3nL probed volume, corresponding to the detection of 5 × 10 −19 cm2.
Abstract: Bragg diffraction from volume thermal gratings excited by crossed Gaussian laser beams provides a sensitive measurement of one- and two-photon absorption in fluid solution. The minimum detectable one-photon absorptivity (base e) was αmin = 1.0 × 10−6 cm−1 in a 3.3-nL probed volume, corresponding to the detection of 5 × 10−19 cm2. The two-photon cross section of benzene at 532 was determined by this technique to be 1.5 × 10−51 cm4 sec; detection of benzene two-photon absorption could be accomplished at concentrations as low as 6.4 × 10−4M. The method produces a diffracted signal on a zero background, so that detection of nonradiative relaxation of the sample is limited only by shot noise.
TL;DR: In this article, an analytical solution of the system of second-order coupled wave equations is obtained and applied to the problems of grazing diffraction by a transmission grating, demonstrating that the grating can behave simultaneously as a transmission and a reflection grating.
Abstract: Light diffraction by a volume phase grating with slanted fringes is considered. An analytical solution of the system of second-order coupled wave equations is obtained and applied to the problems of grazing diffraction by a transmission grating. It is shown that a strong backward diffracted wave arises, demonstrating that the grating can behave simultaneously as a transmission and a reflection grating. The diffraction efficiency balance and angular selectivity are analysed.
TL;DR: The invariance of the direction of a given order diffracted by a grating used in conical diffraction when the grating is rotated about a suitable direction is established and this property applies to any reflecting surface.
Abstract: The invariance of the direction of a given order diffracted by a grating used in conical diffraction (i.e., in off-plane mounting) when the grating is rotated about a suitable direction is established. The extension of this property to crossed gratings (2-D gratings) is demonstrated. An explanation of this amazing property is given in terms of Fermat's principle and applies to any reflecting surface.
12 Jun 1985
TL;DR: NTS Super-High Efficiency (SHE) Holographic technology consists of Dichromated Gelatin (DCG) Bragg Reflection Holograms possessing properties that maximum hologram diffraction efficiency (reflection, in good approximation) is close to 99.7% and optical scattering/ absorption losses are below 0.2% as mentioned in this paper.
Abstract: NTS Super-High Efficiency (SHE) Holographic Technology consists of Dichromated Gelatin (DCG) Bragg Reflection Holograms possessing properties that maximum hologram diffraction efficiency (reflection, in good approximation) is close to 99.7% and optical scattering/ absorption losses are below 0.2%. Hence, NTS Reflection Holograms can achieve close to the theoretical limit for several important holographic applications, including dichroic/ polychroic mirrors, high-reflection spectrum-selective filters, spectrum-splitting PV/TPV holoconcentrators, large holographic mirrors for space applications, holographic heads-up displays, holographic fiber couplers, holographic optical elements (HOEs) holographic coders/decoders, holographic window films, holographic chromatic filters, etc. In this paper, we discussed the application of SHE Holographic Technology to concentrator optics including especially solar applications.© (1985) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, a method based on the diffraction of light is presented for producing binary diffraction gratings with arbitrary opening ratios in both x and y directions, and it is shown that using two master gratings of the Ronchi type and utilizing the results of the double diffraction system, it is possible to produce binary gratings having an arbitrary opening ratio.
Abstract: In this paper, a method — based on the diffraction of light — for producing binary diffraction gratings is presented It is shown that using two master gratings of the Ronchi type and utilizing the results of the double diffraction system it is possible to produce binary gratings with an arbitrary opening ratio The results have been extended for a two-dimensional case and it is shown that producing binary grid gratings with arbitrary opening ratios in both x and y directions is also possible
02 Dec 1985
TL;DR: In this paper, the authors present the experience gained up-to-date in the development of holographic solar concentrators and present the techniques used in the generation of high efficiency dielectric volume-holograms of the transmission type.
Abstract: In this report, we present the experience gained up-to-date in the development of holographic solar concentrators. The techniques used in the generation of high efficiency dielectric volume-holograms of the transmission type are presented in detail. These techniques facilitate the manufacturing of holographic lenses with diffraction efficiency in the order of 97%. In order to achieve the high efficiency, the research team has developed sensitizing and film development procedures for dichromated layers whose scattering losses are comparable to those of the unexposed gelatin layer. The manufacturing of the dichromated gelatin layers is performed in-house (30 x 40 cm2) and can easily be extended to large apertures. The layering procedure is a continuous process and is limited at present only by the travel of the motor-driven table top. The reproducibility of the film-thickness for a batch of manufactured 30 x 40 cm2 holographic plates is better than ± 1 μm. The film-thickness variation of the gelatin film averaged over the entire surface of a holographic plate is in the order of 0.2 Pm/cm. Theoretical and experimental results are presented for some relevant parameters that control the diffraction efficiency of the concentrator. Emphasis is placed on the problems encountered when a multiple lens-system (stack) is generated in a single gelatin layer or in an integrated multi-layer hologram.© (1985) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
12 Jun 1985
TL;DR: The development and construction of a production process to manufacture holographic optical elements in dichromated gelatin for head-up displays requires that a tight control over the spectral tuning, spectral bandwidth, diffraction efficiency, scatter, cosmetic appearance and environmental stability be established as mentioned in this paper.
Abstract: The development and construction of a production process to manufacture holographic optical elements in dichromated gelatin for Head-Up Displays requires that a tight control over the spectral tuning, spectral bandwidth, diffraction efficiency, scatter, cosmetic appearance and environmental stability be established. Once control is established, it becomes possible to produce significant changes to the tuning position, spectral bandwidth and diffraction efficiency, so that holographic optical elements can be produced for a range of applications. This paper examines several holographic optical elements produced by Pilkington P. E. Limited, including retrofit combiners, contrast enhancement filters and narrow band reflection filters. The construction, holographic specification and performance of each of these holographic elements will be outlined and discussed.
TL;DR: In this paper, the authors consider the problem of diffraction of a ray optical field by a curved wedge and show the filiation of some diffraction factors and suggest generalization to other problems such as the diffraction by higher order wedges.
Abstract: Methods for handling high frequency fields are briefly reviewed. They are illustrated by the diffraction of a ray optical field by a curved wedge. The necessary formulas are collected or referred to for a direct application to the problem. The corresponding canonical problem, diffraction of a plane wave by a straight wedge, is presented from a point of view that shows the filiation of some diffraction factors and suggests generalization to other problems such as the diffraction by higher order wedges.
TL;DR: In this article, the theory of holographic relaxation experiments is presented with special attention given to nonsinusoidal laser-induced concentration patterns, and diffraction efficiencies are derived at all Bragg orders for photochromic volume gratings created both with crossed laser beams and by means of square-wave intensity patterns.
Abstract: The theory of holographic relaxation experiments is presented with special attention given to nonsinusoidal laser-induced concentration patterns. Diffraction efficiencies are derived at all Bragg orders for photochromic volume gratings created both with crossed laser beams and by means of square-wave intensity patterns. Analytical equations are obtained for the square-wave case. The equations include real and imaginary parts of the complex index of refraction, the wavelength of the probe beam, and time dependence resulting from mass diffusion. Numerical evaluations are presented for first- and second-order diffraction from pure absorption gratings with various optical thicknesses as functions of exposure. It is concluded that square-wave grating profiles with optimized duty factors produce higher diffraction efficiencies under almost all conditions than do profiles created holographically. Square-wave exposure profiles are recommended for use in grating relaxation experiments because of both efficiency and experimental convenience. In general, the time dependence of transient signals is very complicated; but for low efficiencies, i.e., weak gratings, diffraction at the jth Bragg incidence is dominated by a single exponential term having a characteristic time of 1/[D(jK)2] where D is the tracer diffusion coefficient and K is 2π divided by the grating period.
Patent•
28 Mar 1985
TL;DR: In this article, two diffraction gratings are arranged opposite each other across a slab waveguide and incident light beams with wavelengths lambda 1-lambda 5 from an optical fiber are collimated and guided to the 2nd diffraction grating.
Abstract: PURPOSE:To reduce crosstalk due to stray light, etc, and to obtain superior cut-off characteristics by providing two diffraction gratings in an optical path and diffracting incident light at least twice CONSTITUTION:Unequal-period plane diffraction gratings 10 and 11 are arranged opposite each other across a slab waveguide 3 Incident light beams with wavelengths lambda1-lambda5 from an optical fiber 1 are passed through the slab waveguide 3 and demultiplexed by the 1st diffraction grating 10 and they are collimated and guided to the 2nd diffraction grating 11 They are further diffracted by the diffraction grating 11, and converged on a waveguide 4 as a projection light guide and projected by the wavelengths lambda1-lambda5 Consequently, stray light and aberrations generated by the 1st diffraction is removed by the 2nd diffraction to reduce crosstalk, thereby obtaining superior cut-off characteristics