title: Aspheric grating for extreme ultraviolet astronomy.
abstract: A family of plane curves is developed which can diffract incident parallel rays to a point focus. These curves, termed diffractoidal curves, are rotated around an axis to produce surfaces of revolution correspondingly termed diffractoids, whose imaging properties for sources at infinity are studied by ray tracing in a few examples. The paraboloid emerges as a limiting case of the diffractoid. A comparison is made between the stigmatic focusing properties of the diffractoid and the toroidal grating.
authors.forename: S O
authors.initials: SO
authors.lastname: Kastner
authors.forename: C
authors.initials: C
authors.lastname: Wade