28.1 INTRODUCTION

Over the past two decades, grazing incidence optics have transformed observational X-ray astronomy into a major scientific discipline at the cutting edge of research in astrophysics and cosmology. This review summarizes the design principles of grazing incidence optics for astronomical applications, describes the capabilities of the current generation of X-ray telescopes, and explores several avenues of future development.

The first detection of a cosmic X-ray source outside of our solar system was made during a brief rocket flight less than 40 years ago (Giacconi et al., 1962). Numerous suborbital and Spacelab experiments were deployed over the next 15 years to follow up on this exciting discovery (Giacconi et al., 1981), and in 1978 the first general purpose X-ray telescope (the Einstein Observatory) was placed into orbit, followed by EXOSAT, the Roentgen satellite (ROSAT), the Advanced Satellite for Cosmology and Astrophysics (ASCA), and very recently, the Chandra X-ray Observatory and the X-ray Multimirror Mission (XMM). All of these observatories employ grazing incidence X-ray optics of the type investigated by Wolter (1952). The design of Wolter optics and the technologies for fabricating them are presented in Sec. 28.2 following. Kirkpatrick-Baez optics are described in Sec. 28.3, and the development of very high angular resolution X-ray optics is discussed in Sec. 28.4.

28.2 WOLTER X-RAY OPTICS