Varied Line-space Grating Research Articles

Wavefront propagation through the beamline designed for seeding the DESY XUV FEL

A beamline designed to reduce the spectral bandwidth of the DESY XUV FEL is described. The beamline is intended to cover the wavelength range from 6.4 to 50 nm with three variable line spacing gratings. A plane mirror in front of the grating is used to maintain constant magnification in the dispersion direction. The electric field generated by the first undulator at three wavelengths, 6.4, 13, and 25 nm, is propagated through the beamline. The results show that the beamline has the resolution and imaging properties required for seeding the second undulator at these wavelengths.

Design of holographic gratings recorded with aspheric wave-front recording optics for soft X-ray flat-field spectrographs

Abstract Holographic gratings recorded with aspheric wave fronts have been designed by means of the analytic design method so as to have the interchangeability with mechanically ruled varied-line-space (VLS) gratings that were designed for soft X-ray flat-field spectrographs. It is shown that aspheric wave-front recording optics makes it possible to produce large variations in the grating constant (e.g., more than 30% over a ruled area of 50 mm) required for flat-field spectrographs. The imaging properties of the holographic gratings thus designed are discussed from the viewpoint of interchangeability with mechanically ruled VLS gratings.

First-generation holographic, grazing-incidence gratings for use in converging, extreme-ultraviolet light beams

We present two holographic recording solutions that produce gratings suitable for use at grazing incidence in the extreme ultraviolet. The rulings are formed when the interference pattern of two spherical wave fronts is recorded on a planar substrate. Each grating is designed to minimize or eliminate the dominant aberration terms in order to maximize the spectral and spatial resolution of the system. In the first design, the dominant astigmatism term in a power-series expansion of the light path function is eliminated; in the second design, the dominant comatic terms are minimized. Each grating is placed directly in a converging light beam at grazing incidence to provide high system efficiency in the extreme ultraviolet. The aberration control afforded by both recording solutions is excellent, providing detector-limited spatial and spectral resolution over much of the usable bandpass. Furthermore, the aberration control is maintained over a wide range of beam speeds and off-axis angles, thereby outperforming conventional varied line-space gratings for use in the extreme ultraviolet. We discuss the methodology used to develop the recording solutions, model and compare the performance of the gratings, and discuss possible space-based applications for these gratings.

Variable groove spaced grating monochromators for synchrotron light sources

Several generic spectrometer types have been developed for research using VUV light at synchrotron radiation sources. They all have used gratings with a constant groove spacing and they all have tried to incorporate high resolution, high throughput, rejection of second and higher order radiation, and design simplicity in their construction. The use of gratings ruled with variable spaced grooves to reduce defocus, coma, and spherical aberration was suggested almost twenty years ago. An instrument using this grating concept was built five years ago for conventional sources. The first monochromator using a variable line spaced grating was installed at the National Synchrotron Light Source almost two years ago, and a high resolution version of such an instrument has been built at the Synchrotron Radiation Center operated by the University of Wisconsin. In this presentation we review the development of monochromators using variable line space gratings and the possible applications of this type of instrumentation.

Imaging theory of plane-symmetric varied line-space grating systems

We review the focusing properties of a general planesymmetric dispersive system containing a varied line-space (VLS) grating as its dispersive element. A VLS grating is one whose grooves are straight and parallel (when viewed looking down the grating normal) but unequally spaced. Aberration terms for VLS gratings are related to those for holographically produced gratings. The groove pattern is represented by a groove function, which, although less intuitive than the groove spacing, contains information that clearly corresponds to the imaging properties of the grating. The projection of the groove pattern onto the plane tangent to the grating at its center is shown to be useful in describing the focusing properties of the grating; consequently the imaging effects of the curvature of the grating blank itself can be considered separately.

The Extreme Ultraviolet Explorer Mission

AbstractThe Extreme Ultraviolet Explorer mission is described. For the first six months, an all-sky survey will be carried out covering 90 to 750 Å, or essentially the entire extreme ultraviolet (EUV) bandpass. This EUV survey will be made in four bands, or colors: λλ 90-150 Å, 170-250 Å, 400-600 Å, and 550-750 Å. A portion of the sky which is free from the normally intense 304 Å geocoronal helium background will be surveyed at greater sensitivity; the wavelength coverage of this band is from 90 to 400 Å. Following the sky survey portion of the mission, spectroscopy of individual sources will be carried out. Three spectrometers employing novel variable line-space gratings will provide spectra with ~1 Å resolution over the band from 70 to 760 Å. This spectroscopy will be carried out by guest observers chosen by NASA in a manner roughly analogous to the International Ultraviolet Explorer (IUE) guest observer program.

The extreme ultraviolet explorer mission

Abstract The Extreme Ultraviolet Explorer ( EUVE ) mission, currently scheduled for launch in September 1991, is described. The primary purpose of the mission is to survey the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation. The survey will be accomplished with the use of three EUV telescopes, each sensitive to a different segment of the EUV band. A fourth telescope will perform a high sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all-sky survey will be carried out in the first six months of the mission and will be made in four bands, or colors, λλ70–180 A, 170–250 A, 400–600 A, and 500–700 A. The second phase of the mission, conducted entirely by Guest Observers selected by NASA, will be devoted to spectroscopic observations of EUV sources. The performance of the instrument components is described. The mirrors meet the requirements of the mission, with the best mirror having a full width half energy spread of 4″ and a surface finish of 20 A. Prototype thin film bandpass filters have been flown on the Space Shuttle and their performance optimized. Prototype detectors have been developed which have 1680 × 1680 pixel imaging capability (RMS) and up to 80% quantum efficiency. A newly invented, high efficiency grazing incidence spectrometer using variable line-space gratings will provide spectral data with ∼1 A resolution. An end-to-end model of the mission, from a stellar source to the resulting scientific data, has been constructed. Hypothetical data from astronomical sources have been processed through this model and are shown.

The extreme ultraviolet explorer and the local interstellar medium

The Extreme Ultraviolet Explorer (EUVE) mission is described with emphasis on the overall capabilities of the instrumentation and the relevance of the mission to determining parameters of the local interstellar medium. The primary purpose of the mission is to search the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation (100–1000Å). The search will be accomplished with the use of three EUV telescopes, sensitive to different segments of the EUV band. A fourth telescope will perform a high sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all-sky survey will be carried out in the first six months of the mission. The second six months of the mission, conducted entirely by Guest Investigators selected by NASA, will be devoted to spectroscopic observations of selected EUV sources. The instrumentation is now well developed. The mirrors meet the requirements of the mission with the best mirror having a full-width half energy spread of 8 arc seconds and a surface finish of 20Å. Prototype thin film bandpass filters have been flown on the Space Shuttle and their performance optimized. Prototype detectors have been developed which have 600 by 600 pixel imaging capability and up to 80% quantum efficiency in parts of the EUV band. A newly invented, high efficiency, grazing incidence spectrometer using variable line space gratings is under development; prototype gratings have been fabricated which provide 75% of theoretical efficiency. An end-to-end (star to as-received flight data) model of the mission has been constructed. Hypothetical, but realistic, flux data from continuous astronomical sources absorbed by intervening material have been processed through this model and show the ability of the EUVE instrumentation to measure such parameters as the hydrogen to helium ratio of the local interstellar medium.

Variable line-space gratings: new designs for use in grazing incidence spectrometers

An account is given of a fundamentally different approach to the use of variable line-space gratings for grazing incidence spectrometers. In the new approach, the gratings are flat and they are placed to intercept the converging beam from a collecting mirror rather than the diverging beam from a slit. This results in (1) small aberrations over a wide instantaneous range in wavelength, (2) a modest required variation in line spacing across the ruled width, (3) a simultaneous minimization of both the spectral and image height aberrations, and (4) a completely stigmatic zero order image. The slitless arrangement common to these designs is very compact, having no additional length behind the focal plane of the collecting mirror. In-plane and conical fan designs are considered. One combination design, in the form of an echelle spectrometer, is discussed. The designs are considered to represent ideal candidates for moderate to high resolution spectrometers on such missions as the Far Ultraviolet Spectroscopic Explorer (FUSE, now Columbus) and the Advanced X-ray Astrophysics Facility (AXAF).