Large Diffraction Gratings Ruled on a Commercial Measuring Machine Controlled Interferometrically*

The carriage and ways of a Moore No. 3 measuring machine were slightly modified, and to them were added monorail, diamond carriage, and suitable drive and gearing. When placed under interferometric control, the resulting ruling engine produces excellent gratings of previously unattained dimensions. A stabilized laser removes cumulative and periodic screw errors through blank translation control, and through yaw control eliminates fanning that otherwise would result from way curvature. Blanks up to 260×430 mm can be ruled. A number of echelles in sizes up to 210×410 mm (8×16 in.) have been ruled on this B engine at spacings of 10 fringes (316 grooves/mm) and 40 fringes, and at blaze angles from 62° to 79°. Many of these show the high resolving power and freedom from both error of run and Rowland-ghosts characteristic of echelles from the M.I.T. A engine, with satellites, ghosts of all types, and scattered light reduced further in intensity by 1 to 2 orders of magnitude. Still larger gratings are being ruled on the M.I.T. C engine, of capacity 450×635 mm, based on a Moore No. 4 measuring machine, which is now being improved from grating to echelle ruling quality.