Simulation of the effect of the external calibrator bar on the image quality

For the NIKA2 run 7 one of the goal was to test the possibility to use an external calibrator to make a power modulation on the signal. There's several possible advantages for such a technique, the main one being a better measurement of the KID response variation than the tone modulation. If we validate the technique we would like to install this external calibrator into the secondary mirror. This is a delicate operation, that can't be done without a clear proof of the advantages of the technique. So to make this test we installed the calibrator at the middle of the beam in the telescope vertex cabin hole passing through the back structure of the primary mirror; the calibrator is fixed on a bar attached to the side walls of the cabin, as shown on the pictures below:

To know the effects of this installation on the observation I did Zemax simulations. The main outcome can be seen on the following series of images. The 1st series represent the system without the calibrator, and the second series with the calibrator.

• Image 1 = a 3D shaded model representing the ray tracing for 12 fields from the M1 vertex (hole at the centre of the surface of the primary mirror) down to the arrays inside the NIKA2 cryostat; the grey surfaces represent some cabin limits, cryostat, and optical elements.
• Images 2 and 3 = footprint of the central field rays on the primary mirror without the vignetted rays (by the aperture stop at the cold pupil), and PSF of this field on the array surface.
• Images 4 and 5 = footprint of the high elevation edge field rays on the primary mirror without the vignetted rays (by the aperture stop at the cold pupil), and PSF of this field on the array surface.

1. System without the calibrator

2. System with the calibrator