We study the FOV and chromatic aberrations for different configurations including the number of slots, the wavelength bands and materials. The present section shows the results for a single slot at the center of the image. The study was made by increasing the angle of separation of the e-o rays by the WPs deo from 0.68 to 1.28. The range of wedge angles b is [1.7,2.3]. Results for different values of deo are shifted but the over all position is centered in the image (figure 2). Orange rectangles show results with aberration less than 2 pixels. Red rectangles show results that do not overlap
The optimum geometry is given by a separation deo=0.88 and a wedge angle b=2-2.18. The resulting separation of the center of the beams is about 13-15'', big enough to avoid overlapping after consideration of the tolerances in the manufacturing and alignment. Chromatic aberrations in this case are less than 1.6 pixels in J. However, degradation in K becomes important since chromatics aberration increases with wavelength. Optical quality in K band are shown in Annex B.
In this section we summarize the performance of the image polarimetry mode for deo=0.88 and a wedge angle b=28 and we compare it with the performance in image mode. Whilst the encircled energy is more concentrated in the initial optical design (10mm) the results are still acceptable since the pixel 80% of the energy at diffraction. The Strehl ratio at 1.4um in the aberrated image is 0.833, greater than the Marechal's criterion for diffraction limit (SR>0.8). The Strehl ratio is greater for other wavelengths and fields matching the requirements of 80% with a relative margin. Aberrations in a particular field are shown in the spot diagram. The main source comes from chromatism from the WPs but they are still in the order of the 48mm.