1. David Burke Maynooth University Department of Experimental Physics
Optical Simulations
David Burke
Maynooth University
Department of Experimental Physics

2. MODAL MODAL (Maynooth Optical Design and Analysis Laboratory)
Uses Physical Optics and GBM
Verified against GRASP

3. 1. Farfield pattern of Horn (w/ M. Zannoni)
Mario measured the pattern of the horn in the far field in the Lab (at 60 cm)
In MODAL the beam profile was investigated at 10, 20, 30, 40, 50 and 60 cm
The 60 cm data was compared to the data that was obtained by Mario
Results obtained by exciting horn with an on-axis plane wave

4. Farfield pattern of Horn: 220 GHz

5. Farfield pattern of Horn: Comparison with Mario’s result

6. Farfield pattern of Horn:150 GHz

7. Farfield pattern of Horn: Asymmetry of the E and H planes
150 GHz
220 GHz

8. 2. Spreading of beams due to bandwidth
Due to QUBIC operating at a broad range of frequencies the spread of the beam was investigated
Specifically looked at the lower range ( GHz)
Compared the spread with the central frequency in the lower band

9. Spreading of beams due to bandwidth: Results

10. Spreading of beams due to bandwidth: Central cut
The spread data provided a reduction of the FWHM of the central peak

11. 3. Coldstop
Restricted to 200 mm diameter (maximum) circular coldstop due to filter size that can be made in Cardiff
Performed tests in MODAL, only including the mirrors and the coldstop, to see if this smaller coldstop would have much of an effect on the beams on the focal plane
Also tested to see what is the minimum circular diameter at which the instrument shows measurable difference
This occurred at 165 mm diameter

12. Coldstop footprint

13. Coldstop affected beams
Some beams are affected when the coldstop gets small enough (specifically at 165 mm)

14. Coldstop: X21Y06

15. Coldstop: X17Y02

16. 4. Horn ring radii tolerance
Created geometry files with radii variations of 0.05 mm
SCATTER was used to generate the far field plots and these were compared with the ‘perfect’ far field pattern
The lower and higher frequency bands were examined

17. 0.05 mm tolerance: 130 and 190 GHz

18. 0.05 mm tolerance: 150 and 220 GHz

19. 0.05 mm tolerance: 170 and 250 GHz

20. 240 GHz 0.05 mm
Also Lateral shifts, thicker plates

21. 5. Calibration source simulation (w/ M. De Petris)
Winston cone (calibration source) was put on the edge of the horn array
The specifications were obtained from D. Buzi and M. De Petris
Positioned at (0, ,0) mm in GRF
50 º FWHM
Simulations were performed in MODAL only including the mirrors
Results were compared with GRASP

22. Calibration source simulation
Simulated results in MODAL matched the results obtained from GRASP
6.57% power from emitted beam captured at focal plane

23. Calibration source simulation
When the source was rotated (24 º as recommended by D. Buzi and M. De Petris) to be centred on the primary, the power on the focal plane was still low (only 3.37% of the emitted power captured)

24. Calibration source simulation
Source was put in centre of the horn array to check the power
Power on the primary – 80.18%
Power on the secondary – 73.98%
Power on the focal plane – 9.51%

25. Calibration source (30 º FWHM)
Investigated the power collected by a cone that had a beam with a FWHM of 30 º
This gave a collected power of 15.58%

26. Future Work Examine the effect of a raised ring on the mirrors
Test tolerance/allignment of the mirror positions in the technical demonstrator at room temperature.
Most urgent, using Zemax