Due to the increasing number of astronomical projects and of their associated instruments, the request of large optics with higher optical performances does not stop growing. An important step in the manufacture of these optics is the deposition of high-precision optical coatings. To answer to this request, we developed dichroic coatings, with sharp transition for large optics, working at different angles of incidence and spectral ranges. The work done for the dichroic optics of the HRS and LRS instruments for the 4MOST project will be presented.
Due to the increase of astronomical projects and of their instruments, the request of large optics with higher optical performances does not stop growing. An important step in the manufacture of these optics is the deposition of high-precision optical coatings.
To answer to this request we developed coatings working at different angles of incidence and spectral ranges on large surface:
- anti-reflective coatings for large lenses with strong curvatures,
- dichroic coatings with sharp transition for large optics.
Main results will be presented on the basis of several examples of realization.
High precision measurements of the filters bandpass used on wide-field imagers mounted on large telescopes is critical for type Ia supernovae studies. A dedicated spectrophotometric bench is used to re-measure the now decommissioned ugriz filters used for the SNLS on CFHT-MegaCam. A full characterization of the optical response with respect to the location on the surface and the angle of incidence was performed for each filter. Strong variation over the filter surface is observed. The impact of the actual response on the observation is evaluated and we demonstrate an improvement with respect to the previous published results (SNLS1 and 2).
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