Multilayer coatings for narrow-band imaging in the extreme ultraviolet

Multilayer coatings for the extreme ultraviolet with high reflectance at a spectral band of interest and zero reflectance at another band to be suppressed have been designed and prepared. Multilayer coatings were designed to maximize normal-incidence reflectance at the O(+) 83.4-nm spectral line and to suppress at the same time radiation at the 121.6-nm hydrogen Lyman alpha line. Fresh Al/MgF(2)/Mo multilayer coatings resulted in high reflection/suppression ratios at the above wavelengths. The coatings also exhibited a dip in reflectance at 102.6-nm Lyman beta. The coatings showed some slow but steady degradation over time that could be partially eliminated by sample cleaning. Al/MgF(2)/Mo multilayer coatings protected with a thin ion-beam-deposited C film were found to give a high reflection/suppression ratio with lower degradation over time.     

Design of a high-resolution extreme-ultraviolet imaging spectrometer with aberration-corrected concave gratings

A high-resolution extreme-ultraviolet imaging spectrometer is designed for the Japanese solar mission Solar-B. A spherical varied-line-space (SVLS) grating and a toroidal uniform-line-space (TULS) grating are chosen as candidates for use in the spectrometer to yield high spectral and spatial resolution within the spectral range 25-29 nm. The spectral image-focusing properties and the mechanical tolerances for fabrication and alignment are compared for the two types of grating. The SVLS design is found to be superior to the TULS design for off-plane spectral images and in ease of fabrication and optical alignment.     

Proposal for aberration-corrected imaging spectrograph

We propose a novel flat-field imaging spectrograph that consists of two plane gratings, four spherical mirrors, and two plane mirrors. The imaging spectrograph is designed in such a manner that the primary and the secondary principal points of the whole optical system for the horizontal direction coincide with those for the vertical direction. In a paraxial approximation, it is essentially aberration free because an entrance slit and an imaging detector are placed on the primary and the secondary principal planes, respectively. Spot diagrams obtained from ray-tracing procedures have indicated that the proposed spectrograph is superior to the conventional Czerny-Turner mounting.     

Off-axis pivot mounting for aberration-corrected concave gratings at normal incidence

The off-axis pivot-point mounting for toroidal uniform line-space (TULS) gratings and spherical varied line-space (SVLS) is presented: One scans the spectrum by rotating the grating about the pivot point. The best choice for the location of the point is discussed: For a monochromator the location is chosen such that the grating is moved approximately along the bisector of the subtended angle; for a spectrometer, it is chosen such that the grating is moved approximately along the direction of the incident ray. Minimizing the spectral defocusing caused by the rotation of the grating determines the optimum length of the pivot arm. The pivot points for TULS and SVLS gratings are found to be located on opposite sides with respect to the normal to the grating. In a comparison of the optical performance, the spectral focusing is similar, but the spatial aberrations can be fewer for a SVLS grating.     

Imaging spectrograph for interstellar shocks: a narrowband imaging payload for the far ultraviolet

We present an imaging spectrometer developed for narrowband imaging at 1035 A with high (approximately 1-arc sec) spatial resolution over a modest field of view (approximately 5 arc min). The instrument is based on a conventional Gregorian telescope with aberration-corrected holographic rulings on the secondary optic. These aberration-correcting rulings enable stigmatic imaging in diffracted light with a minimum number of optical elements, thereby maintaining a high system efficiency. The capabilities of this instrument allow us to map the distribution of UV-emitting material in the hot (approximately 300,000 K) plasma from shocks in supernova remnants. Although this design is optimized for imaging near 1035 A, the basic concept can be applied to provide narrowband imaging or long-slit imaging spectroscopy at any wavelength. In addition, a larger field of view is possible with a corresponding loss in spatial resolution.     

Aspheric wave-front recording optics for holographic gratings

The geometric theory of aspheric wave-front recording optics is extended to include the fourth-order groove parameters that correspond to the fourth-order holographic terms in the light-path function. We derived explicit expressions of the groove parameters by analytically following an exact ray-tracing procedure for a double-element optical system that consists of a point source, an ellipsoidal mirror, and an ellipsoidal grating blank. Design examples of holographic gratings for an in-plane Eagle-type vacuum-UV monochromator are given to demonstrate the capability of the present theory in the design of aspheric wave-front recording optics.     

Interferometric sensor based on coherent imaging of gratings

A sensitive interferometric sensor scheme that is based on coherent imaging of a first phase grating onto a second phase grating, their periods accurately matched, is suggested. Experimental data, obtained with a setup based on the suggested scheme, are presented. The sensor was found capable of measuring an angular tilt of a mirror less than 0.5 microrad. Compared with a previously suggested measuring scheme, the novelty of the one presented here is the inclusion of a second set of gratings, which eliminates measurement ambiguity. Some characteristics of the sensor scheme are discussed.     

Apodizing holographic gratings for the modal control of semiconductor lasers

We first present the fabrication technique of apodizing holographic gratings. Gratings with a spatially variable reflectivity profile were obtained by the interference of two Gaussian beams on a glass plate covered with a photoresist. When the exposure time was short enough to avoid saturation of the photoresist, gratings with a quasi-Gaussian reflectivity profile for the beam reflected in the -1 order were produced; the reflectivity at the center could be as high as 71%, and the half-width of the reflectivity profile at the e(-1) position could be as small as 180 mum. Apodizing gratings were used as the end mirror of the external cavity of a broad-area semiconductor laser. Single longitudinal- and lateral-mode operation was observed over the full range of allowed injection currents.     

浮雕型全息光栅诱导液晶分子取向排列的研究

在玻璃衬底上制备浮雕型全息光栅作为液晶显示器件取向层,分析了液晶层厚度对液晶分子在光栅取向层上排列的影响.发现液晶层厚度约为8μm时,液晶分子是沿光栅沟槽方向一致排列,其显微织构均匀,各点光强均匀一致,两个相同光强的状态周期为90°,周期性的微沟槽是促使液晶分子取向一致的主要原因.     

Deformation of the modulation profile in phase holographic gratings

Among all the parameters that characterize a phase grating, the most difficult to control is the modulation profile of the refractive index. In fact, it covers many scalar parameters that are the Fourier coefficients of the profile. To study the influence of processing baths on the modulation profile, in phase holographic gratings made of dichromated gelatin, we have observed that the shape of the profiles obtained sometimes presents a slight concavity or a convexity in the middle, leading to an increase or a decrease in the diffraction efficiency. We present the experimental results and a numerical study in the form of a theoretical prediction, which confirms the experimental observations.     

Merit function to design holographic gratings for moderate-resolution monochromators

A merit function is proposed and applied to design holographic concave gratings for moderate-resolution monochromators. To justify the validity of the merit function, imaging properties of gratings used for the coma-correction Seya-Namioka monochromator, designed by the present authors, Noda, and Takahashi, are compared through ray tracing and their aberration-correction mechanisms are also analyzed. The capability of the merit function is well demonstrated in the design of holographic gratings for another two moderate-resolution monochromators with different requirements. All the results obtained show that the merit function is not only straight and effective but also manages to balance various aberrations of the concave holographic grating very well.     

Optical perfect-shuffle network implementation by use of an ordinary imaging system and holographic gratings

We describe an approach to achieve the optical perfect-shuffle interconnection network in an ordinary optical imaging system; a holographic grating is inserted in the proper position, and a corresponding spatial filter is inserted in its back focal plane. This approach is simple, and the space-bandwidth product of the optical system can be better utilized. As an experimental demonstration, the perfectshuffle interconnection network is shown in one and in two dimensions.     

Effects of anisotropic diffractions on holographic polymer-dispersed liquid-crystal gratings

Volume gratings fabricated by interferometric exposure using composite materials composed of nematic liquid crystals (LC) and LC diacrylate monomers are discussed in the effects of diffraction properties on different grating formations, such as varying LC content ratios, film thicknesses, and the surface conditions composed of alignment layers and rubbing directions. Diffraction properties are experimentally investigated in the viewpoints of anisotropic diffraction and LC orientation. The polarization-azimuth dependence of diffraction efficiencies as functions of the incident polarization states shows the controllability of anisotropic diffractions based on the effects of different surface conditions.     

Volume gratings for holographic storage applications written in high-quality germanosilicate glass

Volume holographic gratings are written with ultraviolet light in high-optical-quality, commercially available Ge-doped silica films and in Ge-doped optical-fiber preform sections loaded with molecular hydrogen. In the film samples, peak refractive-index changes exceeding 10(-2) and a sensitivity (index change/absorbed energy density) of 0.4 × 10(-7) cm(3)/J are measured. Angular multiplexing of up to 51 gratings is demonstrated in the preform samples.     

Dynamics during holographic exposure in photopolymers for single and multiplexed gratings

Abstract

Under the assumption that at low recording intensity the grating formation process is much slower than the free monomer diffusion, we present a model that describes the dynamics of the holographic grating formation in photopolymers. The model indicates how the beam intensity modulation influences the saturation value of the grating modulation, while the average recording intensity is related in a nonlinear fashion to the process time constant. An extension of this model describes and predicts the recording of a single grating in the presence of an additional mutually incoherent light beam, and the simultaneous recording of angularly mutliplexed gratings. The model is validated by comparing with experimental results obtained using DuPont HRF-150-38 photopolymer.     

Line-focusing holographic mirrors for solar ultraviolet energy concentration

We report on the design and the construction of a 1.3-m(2) UV selective solar concentrator intended for photocatalytic water detoxification processes. This concentrator was made by assembling 30 cm x 30 cm line-focusing holographic mirrors. Holograms with an 80% diffraction efficiency concentrate ~40% of the incident solar energy, which is effective for exciting an aqueous suspension of the TiO(2) photocatalyst, and transmit unnecessary longwave radiation. Major problems, such as the low sensitivity of the dichromated gelatin used for recording the holograms and wavelength dispersion, are discussed.     

Apodizing holographic gratings for dual-wavelength operation of broad-area semiconductor lasers

Apodizing holographic gratings are designed to have a Gaussian reflectivity profile in the -1 order and a complementary reflectivity profile in the specular (0) order. They are obtained by the interference of two Gaussian beams on a glass plate covered with a photoresist. These gratings are intended to be used as the coupler of the external cavity of a broad-area semiconductor laser. When the grating is oriented to get the -1 order counterpropagating with respect to the incident beam, single-longitudinal- and single-lateral-mode operation is obtained. We report on the fabrication technique of an apodizing holographic grating designed to allow lasing on two wavelengths simultaneously, with a preselected wavelength separation. The results obtained with a commercial broad-area laser are presented.