On the production of diffraction gratings II. The generation of helical rulings and the preparation of plane gratings therefrom

Abstract

The paper describes the development at the National Physical Laboratory of Sir Thomas Merton’s method of ruling helical diffraction gratings and of transferring them to plane surfaces. It is shown that the periodic errors inevitable in lathe-cut screw threads can be completely eliminated from helices up to 15000 threads per inch and that by applying the replica process already described, each helix can yield an unlimited number of ghost-free plane gratings. It is also shown that by ruling a grating as one continuous helical groove it is easy to control the distribution of the diffracted energy and to avoid the casual errors which are commonly produced by reciprocating ruling engines.