Development of a large blazed transmission grating by effective binary index modulation for the GAIA radial velocity spectrometer

Abstract

INTRODUCTION Gaia is an ambitious ESA mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. Gaia will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and cinematic census of about one billion stars in our Galaxy. The payload consists of 2 Three Mirror Anastigmat (TMA) telescopes (aperture size ~1.5 m x 0.5 m), 3 instruments (astrometer, photometer and spectrometer) and 106 butted CCDs assembled to a 0.9 Giga-Pixel focal plane. The Radial Velocity Spectrometer (RVS) of Gaia measures the red shift of the stars in the spectral band between 847 nm and 874 nm. The spectrometer is a fully refractive optics consisting of 2 Fery prisms, 2 prisms, a pass band filter and a blazed transmission grating (instrument mass about 30 kg). It is located in the vicinity of the focal plane and illuminates 12 of the 106 Charge Coupled Devices (CCDs). Gaia is in the implementation phase, the launch of the 2120 kg mass satellite is planned in Dec. 2012.

Wide band UV/Vis/NIR blazed-binary reflective gratings: two lithographic techniques investigation

“…2) Both wavefront maps are then For both technologies, the WFE is smaller than 20 nm RMS which is 5 times smaller than the 100 nm RMS space application requirement. Such results have already been demonstrated for e-beam technology [12], but it is striking that although NIL technology is less mature, requests additional process steps and is based on soft PDMS mold, its WFE over 3" size component is also excellent.…”

Wide band UV/Vis/NIR blazed-binary reflective gratings for spectro-imagers: two lithographic technologies investigation

“…E-beam lithography has shown its ability for the manufacturing of transmission type blazed-binary gratings for the Gaia Space Mission [10]. However, many spectrometer designs are based on the application of gratings in reflection.…”

Miniature three-mirror telescope for the thermal infrared

“…Instruments applying binary transmission gratings are, e.g., the GAIA radial velocity spectrometer, Sentinel-4 NIR and Sentinel-5 NIR spectrometers. 2,3 The geometry of a simple binary grating is described mainly by 3 parameters: grating period, groove width and grating depth whereupon the microstructure is implemented directly in the surface of a bulky glass substrate. Such gratings are typically operated in -1 st diffraction order in transmission under so-called Littrow condition.…”