Showing papers on "Diffraction efficiency published in 2002"

Holographic recording in TiO2 nanoparticle-dispersed methacrylate photopolymer films

Abstract: We demonstrate permanent holographic storage in the green with high diffraction efficiency and recording sensitivity in TiO2 nanoparticle-dispersed methacrylate photopolymer films. It is shown that the diffraction efficiency as well as the recording sensitivity significantly increase with an increase of nanoparticle concentration. It is also found that volumetric shrinkage during holographic exposure is noticeably suppressed by inclusion of the nanoparticles.

Fabrication of Fresnel zone plate embedded in silica glass by femtosecond laser pulses

Abstract: We fabricated the Fresnel zone plate by embedding voids in silica glass. We investigated the focusing properties by launching a He-Ne laser beam into the zone plate. The spot size of the primary focal point was 7.0 mum and agreed with the theoretical value of 6.1 mum. The diffraction efficiency was 2.0 %. This technique enables us to make alignment free micro-scale lenses inside bulk materials.

Element-specific X-ray fluorescence microscope and method of operation

Abstract: An element-specific imaging technique utilizes the element-specific fluorescence X-rays that are induced by primary ionizing radiation. The fluorescence X-rays from an element of interest are then preferentially imaged onto a detector using an optical train. The preferential imaging of the optical train is achieved using a chromatic lens in a suitably configured imaging system. A zone plate is an example of such a chromatic lens; its focal length is inversely proportional to the X-ray wavelength. Enhancement of preferential imaging of a given element in the test sample can be obtained if the zone plate lens itself is made of a compound containing substantially the same element. For example, when imaging copper using the Cu La spectral line, a copper zone plate lens is used. This enhances the preferential imaging of the zone plate lens because its diffraction efficiency (percent of incident energy diffracted into the focus) changes rapidly near an absorption line and can be made to peak at the X-ray fluorescence line of the element from which it is fabricated. In another embodiment, a spectral filter, such as a multilayer optic or crystal, is used in the optical train to achieve preferential imaging in a fluorescence microscope employing either a chromatic or an achromatic lens.

Polarization and switching properties of holographic polymer-dispersed liquid-crystal gratings. I. Theoretical model

Abstract: Polarization properties and electro-optical switching behavior of holographic polymer-dispersed liquid-crystal (HPDLC) reflection and transmission gratings are studied. A theoretical model is developed that combines anisotropic coupled-wave theory with an elongated liquid-crystal-droplet switching model and includes the effects of a statistical orientational distribution of droplet-symmetry axes. Angle- and polarization-dependent switching behaviors of HPDLC gratings are elucidated, and the effects on dynamic range are described. A new type of electro-optical switching not seen in ordinary polymer-dispersed liquid crystals, to the best of the author’s knowledge, is presented and given a physical interpretation. The model provides valuable insight to the physics of these gratings and can be applied to the design of HPDLC holographic optical elements.

High-Performance Material for Holographic Gratings by Means of a Photoresponsive Polymer Liquid Crystal Containing a Tolane Moiety with High Birefringence

Abstract: Formation of intensity gratings was studied with two s-polarized (s+s) writing beams in polymer liquid crystals (PLCs) containing a photochromic moiety (azobenzene) and a mesogenic unit (tolane, T-AB; cyanobiphenyl, CB-AB) by means of photoinduced change in alignment of PLCs. Remarkable differences were observed between these two PLCs. T-AB showed higher values of the diffraction efficiency (η) and a faster response than CB-AB. In photoinduced alignment behavior of the PLCs, T-AB exhibited a faster change in alignment than CB-AB with the value of η about 30% in the Raman−Nath regime and the maximum value for modulation of the refractive index (Δn‘) of about 0.08. It was revealed that η and Δn‘ are dependent on the structure of the mesogenic unit. In addition, we attempted the holographic image storage of three-dimensional (3-D) objects in the T-AB films. The 3-D object was reconstructed with high resolution (>5000 lines/mm).

Finite-number-of-periods holographic gratings with finite-width incident beams: analysis using the finite-difference frequency-domain method.

Abstract: The effects of finite number of periods (FNP) and finite incident beams on the diffraction efficiencies of holographic gratings are investigated by the finite-difference frequency-domain (FDFD) method. Gratings comprising 20, 15, 10, 5, and 3 periods illuminated by TE and TM incident light with various beam sizes are analyzed with the FDFD method and compared with the rigorous coupled-wave analysis (RCWA). Both unslanted and slanted gratings are treated in transmission as well as in reflection configurations. In general, the effect of the FNP is a decrease in the diffraction efficiency with a decrease in the number of periods of the grating. Similarly, a decrease in incident-beam width causes a decrease in the diffraction efficiency. Exceptions appear in off-Bragg incidence in which a smaller beam width could result in higher diffraction efficiency. For beam widths greater than 10 grating periods and for gratings with more than 20 periods in width, the diffraction efficiencies slowly converge to the values predicted by the RCWA (infinite incident beam and infinite-number-of-periods grating) for both TE and TM polarizations. Furthermore, the effects of FNP holographic gratings on their diffraction performance are found to be comparable to their counterparts of FNP surface-relief gratings.

Large-scale resonance amplification of optical sensing of volatile compounds with chemoresponsive visible-region diffraction gratings.

Abstract: Micropatterning of the vapochromic charge-transfer salt, [Pt(CNC6H4C10H21)4][Pd(CN)4], on transparent platforms yields transmissive chemoresponsive diffraction gratings. Exposure of the gratings to volatile organic compounds (VOCs) such as chloroform and methanol leads to VOC uptake by the porous material comprising the grating lattice or framework, and a change in the material's complex refractive index, n. The index change is accompanied by a change in the degree of index contrast between the lattice and the surrounding medium (in this case, air), and a change in the diffraction efficiency of the grating. When a monochromatic light source that is not absorbed by the lattice material is employed as a probe beam, only changes in the real component of n are sensed. Under these conditions, the grating behaves as a nonselective, but moderately sensitive, sensor for those VOCs capable of permeating the porous lattice material. When a probe color is shifted to a wavelength coincident with the vapochromic charge-transfer transition of the lattice material, the sensor response is selectively amplified by up to 3.5 orders of magnitude, resulting in greatly enhanced sensitivity and some degree of chemical specificity. On the basis of studies at four probe wavelengths, the amplification effect is dominated by resonant changes in the imaginary component of the refractive index. The observed wavelength- and analyte-dependent amplification effects are quantitatively well described by a model that combines a Kramers-Kronig analysis with an effective-medium treatment of dielectric effects.

Theory and performance of the acousto optic programmable dispersive filter used for femtosecond laser pulse shaping

Abstract: A first order theory of operation of the acousto-optic programmable dispersive filter used for femtosecond laser pulse optimization and shaping is presented. The filter spectral resolution, angular aperture, number of programming points, diffraction efficiency as a function of acoustic power are addressed. The theory takes into account the dispersion effects induced by the Tellurium dioxyde crystal. Wideband or high resolution operations of the filter lead to two different crystal cut optimizations. The applications of the filter concern: i) the simultaneous compensations of high orders phase distorsions and of gain narrowing in laser chains, ii) the coherent control of electronic or vibrationnal transitions in atomic, molecular and condensed matter physics.

Photoinduced permanent gratings inside bulk azodye-doped polymers by the coherent field of a femtosecond laser

Abstract: Permanent holographic gratings were fabricated in bulk azodye-doped polymethylmethacrylate by the coherent field of a femtosecond laser. Optical microscopy and atomic force microscopy observations revealed that the gratings consist of two parts, surface relief gratings on both surfaces and refractive index modulated volume gratings in the interior of the polymers. The diffraction efficiency of the first-order Bragg for the gratings was estimated to be 90%.

Polarization and switching properties of holographic polymer-dispersed liquid-crystal gratings. II. Experimental investigations

Abstract: We have performed a detailed study of the polarization properties and switching behavior of holographic polymer-dispersed liquid-crystal gratings. A theoretical model [ R. L. Sutherland , J. Opt. Soc. Am. B19, 2995 (2002)] is compared with a number of observed phenomena in reflection and transmission gratings made with different types of liquid crystals under a variety of experimental conditions. Anomalous polarization effects are described and interpreted. We show that a wide variation of holographic polymer-dispersed liquid-crystal grating properties can be explained in terms of the statistics of droplet orientational distributions.

Controlling the anisotropy of holographic polymer-dispersed liquid-crystal gratings.

Abstract: In this work we investigate the optical properties of electrically switched transmission gratings fabricated holographically using polymer-dispersed liquid-crystal (PDLC) materials. We have found that the PDLC mixture can be used to control the diffractive properties of the liquid-crystal composite gratings. In one limit the gratings are highly isotropic and in the other limit the gratings are highly anisotropic with a large birefringence. The experimental results are compared to theories that include the birefringence of the grating. From theoretical fits to the experimental data, measurements of the liquid-crystal distribution and alignment are obtained.

Diffractive properties of highly birefringent volume gratings: investigation

Abstract: We have performed a detailed comparison of the predictions of coupled-wave theories of isotropic and anisotropic volume gratings. It is shown that material birefringence can dramatically modify the diffractive properties of volume gratings. The predictions of the coupled-wave theories have also been compared with the diffractive properties of volume gratings fabricated with polymer-dispersed liquid crystals. It is shown that a coupled-wave theory that includes the effects of the birefringence of the liquid crystal must be used to explain the diffraction properties of these highly anisotropic gratings. Information can be obtained about the alignment of the liquid crystal within the composite gratings from comparisons of theory and experiment.

Chromatic-distortion compensation in splitting and focusing of femtosecond pulses by use of a pair of diffractive optical elements.

Abstract: We propose a simple optical system to compensate for chromatic distortion that occurs during fan-out of femtosecond pulses by diffractive optics. The proposed system comprises a pair of diffractive elements, one for splitting an incoming pulse and the other for focusing the split pulses. With an appropriate separation between the elements, chromatic distortion resulting from the spectral bandwidth of a femtosecond pulse is removed, and an array of focused pulses with the same dimensions can be obtained. The theory has been verified through optical and processing experiments with 100-fs, 800-nm pulses.

Research on multi-layer diffractive optical elements and their application to camera lenses

Abstract: We developed the multi-layer diffractive optical elements to operate with visible wavelength region. The principle of the multi-layer diffractive optical elements and application to photographic lens system, EF400mm F4 DO IS USM, is reported.

Optical properties of disperse-red-1-doped nematic liquid crystal

Abstract: We report on the optical properties of nematic liquid crystal cells containing the commercially available liquid crystal E7 doped with the azo dye Disperse Red 1 at concentrations ranging from 0.3% to 1.0%. From polarized absorption measurements an order parameter of S=0.569 was obtained, thus showing that the dye molecules align themselves very well with the liquid crystal's director axis. Optical index gratings were written in the material by overlapping two coherent laser beams at 532 nm. Self-diffraction of the writing beams and diffraction of a probe beam at 670 nm were measured. First-order self-diffraction efficiencies and rise times were found to be linearly dependent upon the dye concentration with a maximum efficiency of 3.29% and a minimum rise time of 10.6 ms. The non-linear index coefficient, n 2, was calculated to be 7.6 × 10-3cm2W-1. The data are consistent with a grating formation based on trans–cis photoisomerism of the dye molecules that leads to a reorientation of the liquid crystal phase. These photonic devices are functional without the application of any external field, they are easily prepared, and have lifetimes in excess of two years without any indication of degradation when stored at ambient temperature.

Grating device with high diffraction efficiency

Abstract: A grating structure with a dielectric coating is disclosed that operates efficiently away from the blaze angle in low order with a high diffraction efficiency and high wavelength dispersion. Such grating structure can be employed in Littrow configuration to provide, for example, cavity feedback in excimer lasers.

Single femtosecond pulse holography using polymethyl methacrylate.

Abstract: Holographic gratings have been written on the surface and inside transparent polymethyl methacrylate (PMMA) with individual 130 fs laser pulses at 800 nm. A surface-relief grating is fabricated by ablation and the diffraction efficiency is measured to be about 20%. A volume grating inside PMMA is formed by the change in the refractive index induced by the two-beam interference fringes. Holographic data storage on the surface is realized when one beam carries information. The stored information can be nondestructively reconstructed when the fluence of the read beam is reduced below the threshold.

High-efficiency holographic volume index gratings in DR1-dye-doped poly(methyl methacrylate)

Abstract: Holographic volume index gratings with high diffraction efficiency (greater than 80%) are recorded in a thick sample of Disperse Red 1-doped poly(methyl methacrylate) with red light (647 nm), which is far away from the absorption peak (488 nm) of the material. Measurements of photoinduced birefringence and polarization holography recording confirm that the azo-dye reorientation mechanism is responsible for the grating formation. Energy coupling between the two writing beams is observed even when the incident beams have equal intensity.

Characterization of T-ray binary lenses.

Abstract: Multilevel phase-shift Fresnel diffractive zone plates fabricated on silicon wafers have been used as T-ray imaging lenses. The imaging results, including spatial and temporal distribution of T-rays measured at the focal planes in the frequency range from 0.5 to 1.5 THz, indicate that the performance of the diffractive terahertz (THz) lens is comparable with or better than that of conventional refractive THz lenses. The unique properties of the T-ray binary lens make it possible to fabricate excellent optics for narrow-band THz applications.

Efficiencies of master, replica, and multilayer gratings for the soft-x-ray-extreme-ultraviolet range: modeling based on the modified integral method and comparisons with measurements

Abstract: The near-normal-incidence efficiencies of a 2400-groove/mm holographic master grating, a replica grating, and a multilayer grating are modeled in the soft-x-ray-extreme-ultraviolet (EUV) regions and are compared with efficiencies that are measured with synchrotron radiation. The efficiencies are calculated by the computer program PCGrate, which is based on a rigorous modified integral method. The theory of our integral method is described both for monolayer and multilayer gratings designated for the soft-x-ray-EUV-wavelength range. The calculations account for the groove profile as determined from atomic force microscopy with a depth scaling in the case of the multilayer grating and an average random microroughness (0.7 nm) for the short wavelengths. The refractive indices of the grating substrate and coatings have been taken from different sources because of the wide range of the wavelengths (4.5-50 nm). The measured peak absolute efficiency of 10.4% in the second diffraction order at a wavelength of 11.4 nm is achieved for the multilayer grating and is in good agreement with a computed value of approximately 11.5%. Rigorous modeling of the efficiencies of three similar gratings is in good overall agreement with the measured efficiency over a wide wavelength region. Additional calculations have indicated that relatively high normal incidence efficiency (of at least several percent) and large angular dispersion in the higher orders can be achieved in the 4.5-10.5-nm range by application of various multilayer coatings.

Hybrid metallic-dielectric grating

Abstract: A diffraction grating includes a metallic base layer and layers of dielectric materials of varying refractive index, where a bottom interface of the layers is adherent to the metallic base layer. The dielectric layers are periodically spaced on top of the metallic base layer, leaving the metallic base layer exposed in regions. This grating allows for the polarization insensitive reflective properties of the base metallic layer to operate in conjunction with the polarization sensitive diffraction properties of the multilayer grating structure to provide near 100% diffraction efficiency over a reasonable wavelength bandwidth, independent of the polarization of the incident beam.

Permanent polarization gratings in photosensitive Langmuir–Blodgett films for polarimetric applications

Abstract: The study of a diffractive device for polarimetric applications is reported. The device consists of a diffraction grating recorded by two interfering opposite circularly polarized beams and is based on a Langmuir–Blodgett film of an azo-compound material. This material provides long-time stability and high photoinduced birefringence that makes the grating highly diffraction efficient. We show how polarization gratings permanently stored in these films are suitable for applications as photopolarimeter components.

Inscription of holographic gratings using circularly polarized light: influence of the optical set-up on the birefringence and surface relief grating properties

Abstract: The polarization properties of the optical set-up used for holographic recording of diffraction gratings on azopolymer thin films are analyzed. The state of polarization of circularly polarized light is fully analyzed after reflection on a mirror at various incidences (Lloyd-mirror set-up). The Stokes analysis is performed using a photopolarimeter and the phase shift, the ellipticity and the azimuth orientation are compared with those calculated from Fresnel formulae. At large angles of incidence, an initially right circularly polarized (RCP) beam becomes elliptically polarized with an azimuth of nearly +45°. From these results, holographic diffraction gratings are recorded on an azobenzene-containing polymer thin film using (i) co- and contra-circularly polarized beams and (ii) a right circularly polarized beam interfering with a +45° linearly polarized light beam. Using Jones-matrix formalism, the polarization states of the diffracted orders from the birefringence (Δn) and the surface-relief (2Δd) gratings are derived and compared with experimental measurements. Finally, the induced local birefringences and surface-relief amplitudes are discussed in connection with atomic force microscopy measurements. The diffraction efficiencies obtained under the (+45°+RCP) and (LCP + RCP) (where LCP = left circularly polarized) configurations are thus compared and discussed.

High-efficiency blazed diffractive optical elements for the violet wavelength fabricated by electron-beam lithography.

Abstract: Blazed diffractive optical elements (DOEs) were studied for the violet wavelength by electron-beam lithography By optimizing electron-beam writing parameters and electron-dose distributions, we fabricated eight kinds of grating (period A = 10-054 microgm) with excellent blazed structure It has been demonstrated that the measured diffraction efficiency values agreed well with the rigorous theoretical ones For the fine period of 054 microm, we confirmed a peak appearance of 756% (TE) experimentally A wave aberration as small as approximately 001 lambda (rms) was obtained for the first-order diffracted wave from the fabricated DOEs Blazed DOEs for the violet wavelength could be used as key devices in a high-density optical disk pickup of the next generation

Diffractive optical element and optical head using the same

Abstract: A diffractive optical element emits substantially zero order diffracted light when light with a wavelength of 0.35 μm to 0.45 μm is incident and emits substantially first-order diffracted light when light with a wavelength of 0.6 μm to 0.7 μm is incident. The diffractive optical element includes a substrate and a grating portion formed on the substrate. The grating portion has a step-wise cross section with any one of levels selected from four levels, five levels and six levels. The diffractive optical element emits substantially zero-order diffracted light when light with a first wavelength λ1 satisfying the relationship: 0.35 μm≦λ1≦0.45 μm is incident and emits substantially first-order diffracted light when light with a second wavelength λ2 satisfying the relationship: 0.6 μm≦λ2≦0.7 μm is incident.

Simulation of high-resolution x-ray zone plates.

Abstract: A full-wave approach to quantitative characterization of x-ray zone plate lenses is proposed. Distributed focusing efficiency η(z) of a multifocus optical element is defined as the energy flux through the Airy disk of a reference perfect lens with variable focal length z. Maxima of this function characterize diffraction efficiencies and spatial resolution of the zone plate foci. The parabolic wave equation is used to take into account diffraction effects inside the optical element. Rough and fuzzy interface models are introduced to describe realistic zone profiles. Numerical simulation reveals the limited capability of zone width reduction to improve the zone plate imaging performance. The possibilities of second-order focus enhancement by optimization of the zone plate thickness, line-to-space ratio, and zone tilt are studied numerically.

Accurate diffraction efficiency control for multiplexed volume holographic gratings

Abstract: We report the method of accurate diffraction efficiency control for multiplexed volume holographic gratings in dry photopolymer films (DuPont HRF-600). Based on the experimental evaluations of the grating formation characteristics in dry photopolymer films, we present the way to develop the practical recording schedules for the fabrication of holographic gratings under accurate diffraction efficiency control. Using this method, we obtained single holographic gratings with the desired diffraction efficiency (variation 2.5%) and high-efficiency equal-strength (47%/ 47%) double holographic gratings. As a practical application, we demonstrated the centralized optical backplane architecture with uniform fanouts using the single and equal-strength double holographic gratings we recorded.

Metallic inductive and capacitive grids: theory and experiment.

Abstract: We present theoretical modeling and experimental validation of both capacitive (dot) and inductive (hole) metallic crossed gratings in the mid-infrared (2–5 μm). The gratings are fabricated by use of interferometric lithography and modeled by use of rigorous coupled-wave analysis. Our experimental and numerical investigations of the transmittance spectra of these gratings suggest that, as in inductive grids, the behavior of capacitive grids is described by the coupling of the incident light into surface plasma waves.