Mechanically Ruled Stigmatic Concave Gratings

Abstract

Concave gratings that form stigmatic images in normal incidence spectrographs are analyzed and a new method of ruling stigmatic concave gratings has been developed. The ruling engine is numerically controlled for varying the groove spacings and is capable of ruling both straight and curved grooves. Three types of concave gratings, one conventional and two stigmatic have been ruled and the imaging properties of them are examined. From the results of the examination, the possibility of producing mechanically ruled stigmatic concave gratings with the freedom of choosing stigmatic wavelengths is proved.