The following article describes the coatings of both Fabry-Perot (FP) etalons to be installed in the integral
field spectrometer 3D-NTT. This simultaneous use of two FP etalons of high and low resolution respectively
is the new concept upon which the 3D-NTT is built. Design and fabrication of the coatings of those etalons is
a critical step to be able to achieve the desired performances of the instrument. More precisely, these etalons
will have to show less than a 10% variation of the finesse from 370 to 900nm and a better than lambda/100
cumulative optical uniformity over a Ø100mm surface. The aim is thus to design high-reflectivity coatings for
each of the FP etalon. The design process of the two sets of coatings will be described first, then the expected
performances of each etalon will be presented and finally the progresses in the making of these coatings will be
The 3D-NTT is a visible integral field spectro-imager offering two modes. A low resolution mode (R ~ 300 to 6 000)
with a large field of view Tunable Filter (17'x17') and a high resolution mode (R ~ 10 000 to 40 000)
with a scanning Fabry-Perot (7'x7'). It will be operated as a visitor instrument on the NTT from 2009.
Two large programmes will be led: "Characterizing the interstellar medium of nearby galaxies with 2D maps of
extinction and abundances" (PI M. Marcelin) and "Gas accretion and radiative feedback in the early universe" (PI J.
Bland Hawthorn). Both will be mainly based on the Tunable Filter mode. This instrument is being built as a
collaborative effort between LAM (Marseille), GEPI (Paris) and LAE (Montreal). The website adress of the instrument
is : http://www.astro.umontreal.ca/3DNTT