1. PACS IQR13 Jan 2005 Optical Plans PFM 1 Optical Qualification and Plans for PFM N. Geis MPE

2. PACS IQR13 Jan 2005 Optical Plans PFM 2 Alignment precision achieved for CQM (PACS-KT-PR-014) Alignment made at KT, at ambient, with VIS light. All offsets refer to TEL focus/LOSMeasREQ Alignment Cube  OB< 0.3 mm position0.5 mm (for satellite alignment) < 0.4’ angle 1’ OB  detector arrays (VIS)< 0.3 mm position0.5 mm (internal alignment) < 5’ angle 1’ ( = linear resolution limit at Lyot stop) “M2”  ext. Alignment Mirr< 0.3 mm position0.5 mm (to transfer alignment to MPE OGSE) < 0.3’ angle 0.5’ except #4, all requirements are met => Repeat for PFM. 5’ angle could be improved to ~ 3’, but IIDA/B requirement of 1’ unlikely to be verifiable/achievable FPFPU Alignment

3. PACS IQR13 Jan 2005 Optical Plans PFM 3 Alignment precision achieved for CQM (ILT tests) Descoped program allowed neither characterization of OGSE, nor of CQM. Measurement precision achievable with test equipment is < 0.2 mm position < 0.3’ angle  OGSE suitable for verifying at the PFM requirements level. 1)Test Optics  Cryostat OBnot done 2) Test Optics  FPFPUdone (see next slide) by evaluation from 1) and 2)  3)FPFPU  Cryostat OB not done (missing 1...) FPFPU Alignment Full PFM verification program should suffice to demonstrate PFM alignment at requirements level. However …

4. PACS IQR13 Jan 2005 Optical Plans PFM 4 Caveats Known dimensional problems in OGSE, affecting the internal calibration path. For CQM, ad-hoc (large) alignment corrections had to be applied. For PFM tests, tracking and fixing of problem may be necessary. => Manufacturing changes in OGSE and re-alignment ( ~ 2 month effort). Stability of Test Cryostat 1. Unexpectedly large shift (4mm) in LOS to external ( point) sources on cool-down of test cryostat. 2. After warm-up a residual LOS shift of 0.43 mm remained. (This effect may be responsible in part for 1 mm boresight shift observed between VIS and IR cooldowns -- other contribution: mechanical distortion of chopper ass’y, defocus see 3.) 3. Tilting the cryostat shifts the external LOS by 2 mm (caused by hardware failure?). 4. Possible defocusing of external sources by ~ 10 mm ( reason unclear) Either - fix these shifts by hardware mod. (unlikely) (1-2 month delay of OGSE test program) - characterise effect (repeatability) -- may not be repeatable (1 month / cool-down) - modify test cryostat to allow monitoring/compensation of internal alignment during ILT measurements. (1-2 month delay of OGSE test program) FPFPU Alignment

5. PACS IQR13 Jan 2005 Optical Plans PFM 5 FPFPU Itself The Good Fairly sharp images, in photometry and spectroscopy modes, close to expectations (see presentation by E. Sturm). Peak Strehl not reached within nominal focussing range of OGSE, PSF FWHM ~ 30% too wide. → optical system basic performance qualitatively verified, however focus mismatch between OGSE focus and PACS focus, reason unknown. Reduction of PSF peak height should be easily noticeable in the 105  m photometer band when defocussing by ~ 3 mm. (informal test, but confirms the focussing requirements for best performance claimed by PACS in the IID-B) Further details are still under analysis, but no show stoppers have been flagged in the imaging area as yet. FPFPU Optical Performance

6. PACS IQR13 Jan 2005 Optical Plans PFM 6 FPFPU Itself The Ugly Grating “Ghosts” Full Scans of the spectrometer section during CQM ILTs showed unexpected deviations from expected SED (see next slide): –“Bumps” of ~ 10-50% of total power over an extended wavelength range in 1st order. –Extremely strong spikes at the long-wavelength end of each order. This added signal – which moreover seems to vary for different pixels – may prevent proper calibration of astronomical spectra (line-continuum ratio, e.g.). => Non sequential ray trace model for spectrometer section in progress to identify causes. FPFPU Optical Performance

7. PACS IQR13 Jan 2005 Optical Plans PFM 7 Representative Spectrum from ILT 200 3rd order leak & 0th order ghost 2 pass ghost 2nd order leak & 0th order ghost H 2 0 features

8. PACS IQR13 Jan 2005 Optical Plans PFM 8 - Plot of Ghost Responses in 1st Order 0thorder0thorder Leak 2nd order Ghost 2nd order 2pass Ghost 1st order 2pass Normal Signal Ghost 1st order 3pass

9. PACS IQR13 Jan 2005 Optical Plans PFM 9 - Plot of Ghost Responses in 2nd Order 0thorder0thorder Leak 3rd order Ghost 3rd order 2pass Ghost 2nd order 2pass Normal Signal Lambda Set [um] Lambda Seen [um] 107 65 70 106

10. PACS IQR13 Jan 2005 Optical Plans PFM 10 - Plot of Ghost Responses in 3rd Order 0thorder0thorder Leak 4th order Ghost 4th order 2pass Ghost 3rd order 2pass Normal Signal Lambda Set [um] Lambda Seen [um] 75 50 53 74

11. PACS IQR13 Jan 2005 Optical Plans PFM 11 Grating “Ghosts” … Ongoing Work Preliminary results of a simplified optical model of the Collimator-Grating assembly using non-sequential raytracing Leakage from next higher order affects the long wavelength end of each operating order: this is normal and can be explained/expected from the tail of the filter blocking curves. The high temperature of the telescope background enhances the effect such that it becomes important over a ~ 5–10  m wavelength range. “Interesting” ray paths to detector array identified (see following slides). The observed sharp spectral spikes at longest wavelength, and some surrounding extended signal are caused by 0th order ( = direct mirror) reflection from the grating, ghosting into the beam path via Collimator 1 mirror (see following slides). A broad, 10-50% excess near 170-180  m is caused by a double pass of the grating in 2nd order (Ghost- ~ 105  m) supported by Collimator 2 acting as a retro-reflector. The signal is strong because of the short wavelength involved. Bounded on one side by blocking filter curve, on other side by falling off the mirrors. FPFPU Optical Performance

12. PACS IQR13 Jan 2005 Optical Plans PFM 12 Beam Path of 0th Order Ghost, Simple Baffle Baffle Coll 2 Coll 1 Grating “Det.” Input Slit

13. PACS IQR13 Jan 2005 Optical Plans PFM 13 Beam Path of 2nd Order 2pass Leak, Mechanism

14. PACS IQR13 Jan 2005 Optical Plans PFM 14 Beam Path of 2nd Order 2pass Leak, simple baffle Black baffle Coll 2 Coll 1 Grating “Det.” Input Slit

15. PACS IQR13 Jan 2005 Optical Plans PFM 15 2 (Preliminary) Baffles in place Black baffle Coll 2 Coll 1 Grating “Det.” Input Slit Black baffle

16. PACS IQR13 Jan 2005 Optical Plans PFM 16 - Plot of Ghost Responses in 1st Order 0thorder0thorder Leak 2nd order Ghost 2nd order 2pass Ghost 1st order 2pass Normal Signal Ghost 1st order 3pass

17. PACS IQR13 Jan 2005 Optical Plans PFM 17 - Plot of Ghosts, 1st Order, with Baffles Leak 2nd order Ghost 2nd order 2pass Ghost 1st order 2pass Normal Signal

18. PACS IQR13 Jan 2005 Optical Plans PFM 18 Ghost Responses Magnitude

19. PACS IQR13 Jan 2005 Optical Plans PFM 19 Grating “Ghosts” Several identified… Possible fixes Mounting of additional baffles in Collimator-Grating area. This means Modification of FPU ! Simple blocking baffles Try to find positions for baffle(s) which maximise suppression of unwanted beam paths, while minimising vignetting for normal beam. Trade-off necessary. Some losses expected (5-10%), mostly at long wavelength. Can block most, but not all rogue paths. Minor modification of FPU, qualification of design change could be handled by analysis/similarity. Needs to happen very soon, since all PFM parts have already been manufactured, black-painting run imminent. FPFPU Optical Performance

20. PACS IQR13 Jan 2005 Optical Plans PFM 20 Consequences for PFM Programme Spectrometer Ghosts need to be fixed, fix ready to be implemented soonest Feb. 2005. Manufacturing/assembly of PFM collimator section will have to be delayed. However, overall PFM M/I schedule is probably not affected yet. Proper re-alignment and characterisation/calibration of OGSE and test cryostat, including hardware modifications, will take 5 months (no margin), worst case 8 months, starting mid Jan. 2005. Still compatible with PFM schedule. Schedule extremely tight - no margin. For the PFM there will be a full performance characterisation. Summary