Jeffrey S. Gum

Normal incidence reflectance of ion beam deposited SiC films in the EUV

Results are presented from an experimental investigation of the normal-incidence reflectance at 58.4, 92.0, and 121.6 nm wavelength of 30- and 80-nm-thick SiC films produced by ion-beam deposition on unheated 5 x 5-cm microscope slides. The films were deposited in the 2-m evaporator described by Bradford et al. (1969) with chamber base pressure 1 microtorr, operating pressure 40 microtorr, and a 50-62-mA 750-eV Ar ion beam; the reflectance measurements were obtained in the reflector-monochromator system described by Osantowski (1974). Reflectances of over 30 percent were found at 92 and 121.6 nm, almost equal to those of polished CVD films of SiC and degrading only slightly after aging for 4 months. It is suggested that ion-beam deposition may be the best low-temperature technique for coating EUV optics for space astronomy.

Optical coating technology for the EUV

Abstract Advances in optical coating and materials technology have been one of the key motivators for the development of missions such as the Far Ultraviolet Spectroscopic Explorer recently selected by NASA for an Explorer class mission in the mid 1990s. We review the performance of a range of candidate coatings for normal incidence and glancing incidence applications, and discuss strengths and problem areas for their use in space. The importance of recent developments in multilayer films, chemical vapor deposited SiC (CVD-SiC) mirrors, and SiC films are discussed in the context of EUV instrumentation design. For example, the choice of optical coatings is a design driver for the selection of the average glancing angle for the FUSE telescope, and impacts efficiency, short wavelength cut-off, and physical size.

Extreme ultraviolet performance of a multilayer coated high density toroidal grating.

The performance of a multilayer coated diffraction grating has been evaluated at EUV wavelengths both in terms of absolute efficiency and spectral resolution. The application of a ten-layer Ir/Si multilayer coating to a 3600-lines/mm blazed toroidal replica grating produced a factor of 9 enhancement in peak efficiency near the design wavelength approximately 30 nm in first order, without degrading its excellent quasistigmatic spectral resolution. The measured EUV efficiency peaked at 3.3% and was improved over the full spectral range between 25 and 35 nm compared with the premultilayer replica which had a standard gold coating. In addition, the gratings spectral resolution of >5000 was maintained.

Performance of multilayer coated diffraction gratings in the EUV

Performance of multilayer coated diffraction gratings has been evaluated in the extreme UV. The application of multilayer coatings to two blazed gratings has produced a significant enhancement in grating efficiency in the 300-A spectral region in first order.

Design and fabrication of a 40-cm-diameter SiC-coated normal incidence telescope and spectrometer

The optics of a Dall-Kirkham telescope and a Rowland grating have been coated with ion- beam-sputtered SiC in the 2-m mirror coating facility at Goddard Space Flight Center with a newly acquired deposition system. During the deposition system test runs we verified two optical properties of thin SiC films that had been suggested from calculations: (1) the visible reflectivity is sensitive to the thickness of the SiC layer and (2) a substrate of Al (as opposed to glass) improves the visible reflectivity of the coatings. In addition, we found the slow decay in the far-UV reflectivity exhibited by ion-beam-sputtered SiC coatings stored in a desiccator could be significantly retarded by storage in vacuum. We present the far-UV effective area of the telescope and spectrometer that we plan to fly on NASA sounding rocket 36.109UG in September 1993.

High-reflectance coatings for space applications in the EUV

Advances in optical coating and materials technology have made possible the development of instruments with substantially improved efficiency and made possible to consider more complex optical designs in the EUV. The importance of recent developments in chemical vapor deposited silicon carbide (CVD-SiC), SiC films and multilayer coatings is discussed in the context of EUV instrumentation design. The EUV performance of these coatings as well as some strengths and problem areas for their use in space will be addressed.

High-reflectance coatings and materials for the extreme ultraviolet

Advances in optical coating and materials technology have made possible the development of instruments with substantially improved efficiency in the extreme ultraviolet/far ultraviolet (EUV/FUV) spectral region. For example, the development of chemical vapor deposited (CVD) SiC mirrors provides an opportunity to extend the range of normal incidence instruments down to 60 nm. The EUV performance and some applications of optical coatings including MgG2 protected aluminum, CVD- SiC, SiC films, boron carbide films, and multilayer coatings will be discussed. Contamination sensitivity and cleaning will be addressed.

Large volume, optical and opto-mechanical metrology techniques for ISIM on JWST

The final, flight build of the Integrated Science Instrument Module (ISIM) element of the James Webb Space Telescope is the culmination of years of work across many disciplines and partners. This paper covers the large volume, ambient, optical and opto-mechanical metrology techniques used to verify the mechanical integration of the flight instruments in ISIM, including optical pupil alignment. We present an overview of ISIMs integration and test program, which is in progress, with an emphasis on alignment and optical performance verification. This work is performed at NASA Goddard Space Flight Center, in close collaboration with the European Space Agency, the Canadian Space Agency, and the Mid-Infrared Instrument European Consortium.

EUV performance of a multilayer-coated high-density toroidal grating

Performance of a multilayer coated diffraction grating has been evaluated in the EUV. The application of a multilayer coating to a blazed toroidal grating of high ruling density has produced a significant enhancement in grating efficiency in the 30 run spectral region in first order and has maintained the excellent quasi stigmatic spectral resolution of the grating.

A toolbox of metrology-based techniques for optical system alignment

The NASA Goddard Space Flight Center (GSFC) and its partners have broad experience in the alignment of flight optical instruments and spacecraft structures. Over decades, GSFC developed alignment capabilities and techniques for a variety of optical and aerospace applications. In this paper, we provide an overview of a subset of the capabilities and techniques used on several recent projects in a “toolbox” format. We discuss a range of applications, from small-scale optical alignment of sensors to mirror and bench examples that make use of various large-volume metrology techniques. We also discuss instruments and analytical tools.