The effect of unit lens alignment and surface roughness on x-ray compound lens performance

The required alignment tolerances and surface roughness for unit lens eleme nts in a compound refractive lens (CRL) for x rays are discussed. Contrary to what one might expect and what has been stated in the patent literature, alignment tolerances are large and for typical parameter values the effect of misalignment is minor. For a parabolic lens the focusing properties of the CRL are unaltered by misalignment and there is a small increase in abso rption. For a lens with spherical aberration, there is a slight change in f ocal length, a minor translation of the image, and a small increase in abso rption. This article also shows that lens gain is not appreciably reduced i f the phase shift that is introduced by the roughness is limited to +/- pi /4 or if the transverse period of the roughness exceeds a specified value. The CRL can benefit from a managed misalignment of the elements to reduce t he phase error introduced by surface imperfections of the lens. (C) 2001 Am erican Institute of Physics.