Large Astronomical Diffraction Gratings

Large astronomical gratings have ruled areas from 128 x 254 mm to 304 x 406 mm. The requirement for even larger gratings for ground-based astronomical telescopes has led to three alternative solutions: a static fixture to hold smaller gratings in a larger configuration, an adjustable fixture with optical feedback to move the gratings with respect to each other to maintain focus, and a mosaic grating produced by combining two high accuracy multiple replication gratings onto a single substrate. Such monolithic mosaic gratings have the advantage of long-term alignment stability over the other two alternatives.

In the 1990s, Richardson Gratings developed the capability to replicate two large submaster gratings onto one monolithic substrate. Except for a “dead space” between the two replicated areas, the entire face of the larger product substrate contains the groove pattern. This mosaic grating must have its two grating areas aligned to very high accuracy if the mosaic is to perform as one high-quality grating. Typical specifications for two 308 mm x 408 mm ruled areas on a 320 mm x 840 mm substrate are one arc second alignment of the groove directions, one arc second tilt between the two faces, and one micron displacement between the two grating planes.

The gratings below are suitable for use in astronomical instrumentation and are listed in order of groove frequency, with the lowest blaze angle listed first. Blaze wavelengths listed are for the first-order Littrow configuration. The maximum ruled area is groove length x ruled width. Click on a Master Grating Code (last 4 digits of a grating's part number) below to view master grating efficiency curves. Use the request a quote to get a quote based on your requirements.