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Display of the NIKA PSF simulated with Zemax, including the complete optics

Purpose: help interpretation of features visible in the real beam study.

Preliminary remark: The simulation takes into account the complete optical chain from the primary 30m diameter parabola down to the array with real surfaces shapes (e.g. thick lenses) and stops, but without any fabrications or intrinsic physically induced defaults of the surfaces (e.g. parabola deformation due to gravity and to panels imperfect leveling). So in particular the PSF simulation can't produce the well known 3-components error beams of the 30m telescope (which is described for instance by Greve et al, 1997).

Context

• Figure 1: Distribution on the image plane (array) calculated by the ray tracing algorithm of rays coming from various fields (directions) evenly distributed on a grid pattern on the entrance pupil. Circle diameter = 39 mm, Angular distance between 2 fields diametrically opposed = 2.8'.

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• Figure 2: Spot diagram = Zoom on the ray tracing distribution of each test field (colored dots) showing the extend of the aberrations of the system as compared to the diffractions effects materialized by the contour of the 1^st Airy dark ring (black circles). Typically when the aberration spots are enclosed in the Airy ring, the system is diffraction limited. Oval shape of Airy ring are a symptom of pupil aberrations.

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PSF at optimal focus

• Figure 3: PSF of the central field for the 1mm band central wavelength (top left), PSF of the central field for a representative distribution of wavelengths along the 1mm bandwidth (top center), PSF of several Fields distributed along the edge of the 2.8' FOV for a representative distribution of wavelengths along the 1mm bandwidth (top right and bottom). The tetrapod spider holding the secondary mirror from teh primary is clearly visible. The distortions are dominated by pupil aberration; image aberrations are negligible.

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• Figure 4: enlarged and deeper view of the PSF of the central field for the 1mm band central wavelength (left), and PSF of the central field for a representative distribution of wavelengths along the 1mm bandwidth (right)

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Effect of defocus on the PSF

• Figure 5: PSF of several fields at center and 2.8' FOV border when the telescope is well focused (1^st image), and when the telescope is defocused by 2mm on the lateral X direction (secondary mirror [M2] moved perpendicular to optical axis) (2^nd image).

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• Figure 6: PSF of central field (top graphs) and a field at the 2.8' FOV border [= 1.4' wrt center] (bottom graphs) with M2 moved by +1 mm (left graphs), 0 mm (center graphs), - 1 mm (right graphs) along the Z [=optical] axis (1^st image), along the X axis (2^nd image), and along the Y axis (3^rd image).