Joakim F. Lindblom

Soft X-ray Images of the Solar Corona with a Normal-Incidence Cassegrain Multilayer Telescope

High-resolution images of the sun in the soft x-ray to extreme ultraviolet(EUV) regime have been obtained with normal-incidence Cassegrain multilayer telescopes operated from a sounding rocket in space. The inherent energy-selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The Cassegrain telescopes provided images in bands centered at 173 and 256 angstroms. The bandpass centered at 173 angstroms is dominated by emission from the ions Fe IX Fe X. This emission is from coronal plasma in the temperature range 0.8 x 106 to 1.4 x 106K. The images have angular resolution of about 1.0 to 1.5 arc seconds, and show no degradation because of x-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to overlying cool prominences are visible in the images. The density structure of polar plumes, which are thought to contribute to the solar wind, has been derived from the observations out to 1.7 solar radii.

Thin film filter performance for extreme ultraviolet and x-ray applications

Substantial work has been done to characterize filter materials for the vacuum ultraviolet and x-ray regions of the electromagnetic spectrum. This paper summarizes the theoretical basis for predicting performance and compiles the results of different measurement programs for comparison. Recent work that better quantifies transmission as a function of wavelength for various filter and window materials is reported. Other applications of thin films in which these optical properties are important include photocathodes and x-ray laser targets. Of particular interest are figures giving linear absorption coefficients as a function of wavelength for commonly used filter materials. Also included are recent data on the effect of aging on aluminum filters, plus test data and comments on the use of composite materials designed to adjust the bandpass of a filter to meet particular research requirements. The data are presented so that the reader may more easily design and predict the performance of filters and windows for specific applications.

Multi-Spectral Solar Telescope Array

The development of multilayer optics has profound implications for soft x-ray/extreme ultraviolet (XUV) astronomy. During the October 1987 flight of the Stanford/Marshall Space Flight Center Rocket X-Ray Spectroheliograph, narrow wavelength band, low scatter soft x-ray/extreme ultraviolet spectroheliograms were obtained with ~ 1 arcsec spatial resolution at ? ~ 173 A (Fe IX, Fe X) and at ? - 256 A (He II Ly-?). Although the Cassegrain telescopes used in this experiment were small (63.5 mm diameter) and utilized spherical rather than paraboloidal/hyperboloidal mirrors, the images produced exceed in quality any XUV spectroheliograms previously obtained with either normal or grazing incidence techniques. We describe a new rocket spectroheliograph instrument, the MultiSpectral Solar Telescope Array (MSSTA), that is currently being prepared for launch in August 1990. This instrument will utilize true Ritchey-Chretien optics of 127 mm diameter and parabolic Herschelian optics of 40 mm diameter, which will allow spectroheliograms to be obtained over the soft x-ray/extreme ultraviolet/far ultraviolet spectral range (40 to 1550 A). The performance of this new instrument should definitely demonstrate the unique combination of ultrahigh spatial resolution and spectral differentiation that multilayer optics afford for astronomical observations. The MSSTA will also represent the first astronomical use of an important new optical device, the multilayer grating. The MSSTA should obtain unprecedented information regarding the structure and dynamics of the solar atmosphere in the temperature range 104 to 107 K.

Soft X-Ray/Extreme Ultraviolet Images Of The Solar Atmosphere With Normal Incidence Multilayer Optics

We report on the first high resolution images of the sun in the soft x-ray/extreme ultraviolet (XUV) regime obtained with normal incidence multilayer optics. The images were obtained during a sounding rocket flight on October 23, 1987 from White Sands Missile Range, New Mexico. Multilayer coated optics were used in three different configurations: as optical elements in two Cassegrain Telescopes, as off-axis primary mirrors, and as tertiary mirrors operating with a Wolter Schwarzschild grazing incidence mirror. The inherent energy selective property of multilayer coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. Images were recorded at 173 A and 256 A with the Cassegrain Telescopes, at 256 A with a Herschelian Telescope, and at 44 A, 173 A and 256 A with the Wolter Schwarzschild hybrid telescope. In addition, soft x-ray images in the 8 - 18 A bandpass were obtained at the prime focus of the Wolter Schwarzschild optics. The images show many features of the solar corona and transition region, including magnetically confined loops of hot solar plasma, coronal plumes, polar coronal holes, supergranulation, and features associated with overlying cool prominences.

Multi-Spectral Solar Telescope Array II: soft x-ray EUV reflectivity of the multilayer mirrors

We have developed seven compact soft x-ray/EUV (XUV) multilayer- coated and two compact FUV interference-film-coated Cassegrain and Ritchey-Chretien telescopes for a rocket-borne observatory, the Multi-Spectral Solar Telescope Array. We report here on extensive measurements of the efficiency and spectral band pass of the XUV telescopes carried out at the Stanford Synchrotron Radiation Laboratory.

Design of a Normal Incidence Multilayer Imaging X-Ray Microscope

Abstract Normal incidence multilayer Cassegrain x-ray telescopes were flown on the Stanford/ MSFC Rocket X-Ray Spectroheliograph. These instruments produced high spatial resolution images of the Sun and conclusively demonstrated that doubly reflecting multilayer x-ray optical systems are feasible. The images indicated that aplanatic imaging soft x-ray/EUV microscopes should be achievable using multilayer optics technology. We have designed a doubly reflecting normal incidence multilayer imaging x-ray microscope based on the Schwarzschild configuration. The Schwarzschild microscope utilizes two spherical mirrors with concentric radii of curvature which are chosen such that the third-order spherical aberration and coma are minimized. We discuss the design of the microscope and the results of the optical system ray trace analysis which indicates that diffraction-limited performance with 600 A spatial resolution should be obtainable over a 1 mm field of view at a wavelength of 100 A. Fabrication of several imaging soft x-ray microscopes based upon these designs, for use in conjunction with x-ray telescopes and laser fusion research, is now in progress. High resolution aplanatic imaging x-ray microscopes using normal incidence multilayer x-ray mirrors should have many important applications in advanced x-ray astronomical instrumentation, x-ray lithography, biological, biomedical, metallurgical, and laser fusion research.

Design of an imaging microscope for soft X-ray applications

The objective of this investigation was the design and analysis of an imaging soft x-ray multilayer microscope with a spatial resolution of 0.1 microns. Since the optical aberrations of grazing incidence mirrors are large, and since x-ray scattering effects can severely degrade performance, an x-ray microscope using normal incidence multilayer optics has been designed. Recently, a normal incidence multilayer Cassegrain x-ray telescope was flown and produced high spatial resolution images of the Sun with extremely low x-ray scattering. These images clearly indicate that aplanatic imaging soft x-ray/XUV microscopes should be achievable using normal incidence multilayer optics technology. The microscope we have chosen to investigate is of the Schwarzschild configuration, which consists of two concentric spherical mirrors with their radii of curvature chosen such that the third-order spherical aberration, coma, and astigmatism are minimized. A ray tracing analysis of the optical system has been performed which indicates that diffraction-limited performance can be expected for an object height of 0.2 mm. Plans for fabrication of this imaging soft x-ray microscope will also be discussed.

Astronomical observations with normal incidence multilayer optics : recent results and future prospects

We have obtained high resolution (~1 arcsec) X-ray and EUV images of the solar corona with two rocket-borne normal incidence Cassegrain multilayer telescopes. The Cassegrain images correspond to material at ~1 000 000 K (λ ~ 173 A) and ~ 80 000 K (λ ~ 256 A). Other images, at somewhat lower resolution, were obtained with Herschelian multilayer telescopes and Wolter-Schwarzschild hybrid grazing incidence/multilayer optical systems. We discuss the Cassegrain and Herschelian images, emphasizing the analysis of polar plumes observed at the limb of the Sun. Polar plumes are thought to represent structures that contribute significantly to the flow of coronal material into the solar wind. We will also comment briefly on other coronal features observed, including coronal holes, the chromospheric network, active region loops, and prominence cavities. Multilayer technology represents a major breakthrough in astronomical X-ray and EUV imaging; we will discuss the application of specific multilayer techniques to astronomical observations, emphasizing observations of the sun. We will also report on current efforts in our laboratories to develop a comprehensive Multi-Spectral Solar Telescope Array rocket instrument for the study of a wide variety of problems related to the solar atmosphere.

EUV/FUV response characteristics of photographic films for the Multi-Spectral Solar Telescope Array

The photographic film employed by NASAs Multi-Spectral Solar Telescope Array must have high-to-ultrahigh resolution; since the spacecraft bearing the telescope must be evacuated to prevent the failure of delicate EUV and soft X-ray filters due to acoustic vibration during launch, the films must also have very low outgassing rates. An account is presently given of the properties of important new emulsions selected for flight, together with response-characteristics data for the experimental XUV 100 film and an uncoated Spectroscopic 649 emulsion.

Multi-spectral solar telescope array V; Temperature diagnostic response to the optically thin solar plasma

The authors have developed compact soft x-ray, extreme ultraviolet (EUV), and far-ultraviolet (FUV) multilayer coated telescopes for the study of the solar chromosphere, corona, and corona/solar wind interface. Because these systems operate at short wavelengths ({approximately}40 {angstrom} {lt} {lambda} {lt} 1550 {angstrom}), the modest apertures of 40 to 127 mm allow observations at very high angular resolution (0.1 to 0.7 arcsec). In addition to permitting traditional normal incidence optical configurations to be used at soft x-ray/EUV wavelengths, multilayer coatings also allow a narrow wavelength band ({lambda}/{Delta}{lambda} {approximately} 15 {minus}100) to be selected for imaging. The resulting telescopes provide a very powerful and flexible diagnostic instrument for the study of both the fine-scale structure of the chromosphere/corona interface and the large-scale structure of the corona and corona/solar wind interface. In previous papers, the authors have described a new solar rocket payload, the Multi-spectral Solar Telescope Array (MSSTA), which is composed of 17 of these compact telescopes. In this paper, the authors report on the ability of the MSSTA payload to obtain temperature diagnostic information about the optically thin solar plasma. The authors also discuss applications of this information to studies of coronal structure.