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Quasi-Optical Alignment Status HIFI Consortium Meeting

Quasi-Optical Alignment Status HIFI Consortium Meeting Tuesday 20 April 2004, SRON-Utrecht, The Netherlands Willem Jellema (1,4) , Robert Huisman (1) , Massimo Candotti (2) , Timothy Finn (2) , Neil Trappe (2) ,

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Quasi-Optical Alignment Status HIFI Consortium Meeting

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  1. Quasi-Optical Alignment Status HIFI Consortium Meeting Tuesday 20 April 2004, SRON-Utrecht, The Netherlands Willem Jellema(1,4), Robert Huisman(1), Massimo Candotti(2), Timothy Finn(2), Neil Trappe(2), Anthony Murphy(2), Stafford Withington(3), Pieter Dieleman(1), Nick Whyborn(1), Wolfgang Wild(1,4) (1)SRON, (2)NUIM, (3)University of Cambridge, (4)Kapteyn Institute W.Jellema@sron.nl

  2. Outline of Presentation RT results MSA Band 1 @ 480 GHz RT results LO Port FPU Band 1 @ 480 GHz RT results telescope path FPU Band 1 @ 480 GHz LHe results MSA Band 1 @ 480 GHz (CTH) LHe results LO Port FPU Band 1 @ 480 GHz LHe results MSA Band 5 @ 1130 GHz Conclusions and issues

  3. aperture plane 5 MAM 3 MAM 1 MAM 2 output plane Optical System Description: Mixer Sub-Assembly Optics

  4. MSA-H MSA-V Optical System Description: Mixer Assembly Optics MSA-H MSA-V Tel LO

  5. Optical System Description: Cold Local Oscillator Optics

  6. Optical System Description: Common Optics Assembly

  7. MAM2 MAM1 Horn MAM3 Experimental System (1)

  8. Experimental System (2) MSA-V Y Band 1 AD Band 5 Test source X

  9. Comparison Simulation and Experimental Results: MSA (1) Simulation of MSA Band 1 Measurement of MSA Band 1

  10. Comparison Simulation and Experimental Results: MSA (2) Intensity MSA Band 1 Unwrapped Phase MSA Band 1

  11. Comparison Simulation and Experimental Results: MSA (3) We expect a on-axis symmetric Gaussian beam with waist radius of 3.55 mm In reality we find Associated loss due to diffraction is 3%

  12. Comparison Simulation and Experimental Results: CLO (1) Simulation MSA-V Measurement MSA-V Simulation MSA-H

  13. Comparison Simulation and Experimental Results: CLO (2) Intensity MSA-V Phase MSA-V

  14. MSA-H MSA-V Comparison Simulation and Experimental Results: CLO (3) We expect an on-axis symmetric Gaussian beam with waist radius of 7.5 mm In reality we find Imbalance in on-axis coupling of 4% due to diffraction

  15. Comparison Simulation and Experimental Results: COA (1) Simulation MSA-H Simulation MSA-V Measurement MSA-H

  16. Comparison Simulation and Experimental Results: COA (6) Intensity MSA-H Phase MSA-H

  17. Comparison Simulation and Experimental Results: COA (2) Illumination M2 for MSA-H Illumination M2 for MSA-V

  18. Comparison Simulation and Experimental Results: COA (3) Simulated WFE map for MSA-H Simulated WFE map for MSA-V Measured WFE map for MSA-H ε < /20 ε < /17 ε < /22

  19. Comparison Simulation and Experimental Results: COA (4) Telescope far-field pattern MSA-H Telescope far-field pattern MSA-V  (nominal position) = 71.3%  (nominal position) = 74.6%

  20. Comparison Simulation and Experimental Results: COA (5) Far-field cuts MSA-H after repointing Far-field cuts MSA-V after repointing   5 3dB = 0.7   5 3dB = 0.7  (average position) = 76.8%  (average position) = 75.4%

  21. Summary and Conclusions (1) We have presented accurate near-field simulations and measurements of the FPU Optics of HIFI The agreement between theory and experiment is remarkable. Note that both sets of data were plotted independently in one single absolute coordinate system. The diffraction effects are clearly visible as amplitude and phase asymmetry. Even for a perfectly aligned system the beams at actual wavelengths appear to be misaligned. Dominant effect is tilt or phase slope in pupil plane. The magnitude of these intrinsic effects is of similar order as the required alignment tolerances.

  22. Summary and Conclusions (2) The diffraction effects are different for the two types of MSA because of the asymmetric mounting on the FPU mechanical structure. Consequently there is an imbalance in LO coupling to the two types of MSA of about 4% for a perfectly aligned system. In the telescope path the diffraction effects show up as pointing offset which needs to be corrected for by repointing. The remaining co-alignment error is about 5% of the FWHM.

  23. LHe Results MSA Band 1 @ 480 GHz (CTH)

  24. Parameters of propagation model MSA Band 1 Analyses give different results. Many parameters in CTH analysis not yet known. Scalar analysis method is not sensitive to determine lateral misalignment. Measurement at CTH predicts severe misalignment for LO port FPU Band 1

  25. LHe Results LO Port FPU Band 1 @ 480 GHz (SRON)

  26. Matched Beam Parameters LO Port FPU Band 1 Deviations within tolerance QO Alignment budget Confirm expectations on the basis of RT measurement for the cooled receiver Discrepancy with CTH results. Systematic error in laser triangulation at CTH?

  27. LHe Results MSA Band 5 @ 1130 GHz SNR > 70 dB 29 March 2004: First cryogenic near-field measurement of a lens-antenna SIS mixer integrated in a MSA with absolute alignment and direct phase measurement @ 1.13 THz

  28. Harmonic Generator Test Source for Band 5, 6L and 6H RPG corrugated horn High power doubler 3 stage PA Band 5: #6, f = 1100 – 1250 GHz, P  0.1 W Band 6L: #8, f = 1400-1700, under development Band 6H: #9, f = 1700 – 1900, under development Required power is only a few nW 0.7 mm aperture W-band CW source, JPL three-stage PA chain, high power doubler and varactor diode generator

  29. Direct Comparison to Expected Gaussian Beam

  30. Comparison Matched Gaussian and Measurement

  31. Matched Beam Parameters for MSA Band 5 @ 1130 GHZ Beam waist size and location deviate significantly. Not explained by MU defocus. In addition the lateral and tilt errors exceed the allowed tolerances Discussion with JPL / Caltech about potential sources of error is initiated recently.

  32. C onclusions and Issues (1) We have developed and validated powerful diagnostic tools for QO alignment verification: electromagnetic models and near-field facilities Measurements so far on waveguide mixer bands indicate that good optical performance and accurate alignment is feasible. Issue to be resolved is discrepancy between SRON and CTH results for MSA Band 1. Further development on laser triangulation and direct cross-comparison measurement on same MSA might be needed. Feasibility of phase and amplitude measurements beyond 1.1 THz has been demonstrated and shows very good performance.

  33. Conclusions and Issues (2) MSA Band 5 shows a severe deviation from expected QO interface. In addition we expect that it will be very hard to realize the required alignment accuracy in our current approach (success-oriented, no shimming, no iterations). Given this error the diplexer will not work properly (diffraction loss), internal truncation in the telescope path is expected and this might explain the poor sensitivity when looking at the internal calibration source (analysis ongoing at NUIM) Careful verification of the current lens-antenna near-field interfaces is required. Independent verification of PILRAP with e.g. HFSS is required since PILRAP has never been verified in the near-field (phase and amplitude). Direct lens-antenna measurements in amplitude ans phase with absolute alignment might be needed to support these models.

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