Abstract

The MIT-B 400-mm grating ruling engine has been partially rebuilt mechanically and equipped with a new interferometer displacement measuring system using a He-Ne frequency stabilized laser, polarization beam splitters, and four-phase silicon detector systems. Both translation and rotation are measured and used in feedback correction loops to compensate for lead screw and residual yaw error of the grating carriageways. The signals are digitized with a bit size of 0.088 nm and processed with a high-speed microprocessor designed to handle all control functions, including the cumulative effects of basometric pressure changes on wavelength. All motions are driven by high-efficiency dc servo motors equipped with tachometer feedback and high-resolution angular encoders. The grating carriage is driven at a nominally constant speed, and the diamond carriage motion is retarded or speeded up to compensate for any residual mechanical errors. Digital input provides for all conceivable groove frequencies 20-2000/mm, including programmable variations. Echelle rulings have demonstrated a resolution of over 10⁶ and periodic errors of <1 nm.

© 1987 Optical Society of America