Bulk Transmission Gratings for Astronomy

Holographic Ion Etched Ruled Transmission Gratings

High-efficiency IR transmission gratings (grisms) engraved into fused silica substrates

Rosetta Mission: fly by Mars
Rosetta mission: fly by of Mars

In many astronomy applications, grisms (transmission gratings patterned on a prism) are widely used for in-line disperson of an infrared spectrum.

In the infrared, classical replicated grisms present many limitations. The epoxy layer, necessary for replication, absorbs infrared light. In addition, this epoxy layer compromises the integrity of the grism when used at low temperatures.

To address these issues, HORIBA Jobin Yvon has designed and manufactured transmission gratings which are holographically patterned and etched directly into IR fused silica substrates.

Example of a High Efficiency IR Transmission Grating (GRISM)
Example of a high efficiency IR transmission grating (GRISM) directly etched into an IR grade fused silica substrate

Three grating types were developed, for wavelengths ranging from 1 micron to 2.4 microns. The diffraction efficiency reaches 60% to 70% in natural light.

Engraved directly into fused silica, these gratings can survive very low temperature conditions and vacuum environments.

 

 

 

 

High-efficiency UV transmission gratings (grisms) engraved into CaF 2 substrates

Example of an ion-etched ruled grating profile (into CaF material) made for the GALEX experiment.
Example of an ion-etched ruled grating profile (into CaF material) made for the GALEX experiment.

Through our expertise in ion etching, HORIBA Jobin Yvon has developed a process which allows us to produce optimized groove patterns in CaF2. A master grating is ruled in a gold layer deposited on top of the grating substrate, and then the groove profile is transferred by ion etching directly into the substrate itself. The result is a monolithic sawtooth-profile grating which can withstand extreme temperatures and environmental conditions.

A saw-tooth profile transmission grating, ion-etched directly into a CaF2 substrate for use at 140 nm in second order, has been successfully produced for the GALEX experiments.