Deflector for converting a beam of parallel rays into a beam of rays having constant incidence on cylindrical part

Claim 1

A deflector for converting a beam F of rays parallel to the generating-lines of a cylindrical part C having a polygonal directrix into a beam F'' of rays impinging upon the surface of said part at a constant angle of incidence i so as to generate therein refracted waves in which the sections of the associated wave surfaces along the surface of said part are at right angles to a family of broken helices, each helix being constituted by a plurality of straight-line segments which are concurrent in pairs along the edges of the cylindrical part C, each segment being inclined at an angle Beta with respect to a plane at right angles to the generating-lines of said cylindrical part C, wherein said deflector is constituted by a plurality of flat deflecting elements, at least one deflecting element Mi being associated with each face Pi of said part, the orientation of each flat deflecting element Mi being defined by the direction of its normal ni whose projections are proportional to cos Alpha on a generating-line of the part C, to cos j sin Alpha on a normal to the face Pi and to sin j sin Alpha on an axis at right angles to the two projections aforesaid, the angles j and Alpha being defined from the angles i and Beta by the relations tan j tan i cos Beta and cos 2 Alpha + or - sin i sin Beta and wherein the planes of two flat deflecting elements Mi and Mi 1 associated with two consecutive faces Pi and Pi 1 of the part C are deduced from each other by means of a movement of rotation followed by a movement of translation, said movement of rotation being performed about an axis parallel to the generating-lines of the part C and located in a plane which is equidistant from the edges Ai and Ai 1, the edge Ai being at the intersection of the faces Pi 1 and Pi and the edge Ai 1 being at the intersection of the faces Pi and Pi 1, the angle of rotation being equal to that of the dihedron constituted by the faces Pi and Pi 1, and the movement of translation being performed in a direction parallel to the generating-lines by a quantity a sin j tan Alpha , where a is the width of the face Pi.