FM FPU Subunits

1
FM FPU Subunits

• A. Poglitsch

2
Performance of FPU and Subunits (I)

• Structure
• Temperature (stability) requirements
• Mechanical/optical tolerances, alignment
• Mirrors
• Optical performance
• Chopper
• Pointing accuracy
• Dynamic behaviour (duty cycle)
• Grating
• Optical performance of grating
• Mechanical performance of grating drive
• Precision of position readout/actuator jitter
• Dynamic properties (scanning/dithering/frequency
  switching)

3
Performance of FPU and Subunits (II)

• Filters
• In-band transmission
• Out-of-band suppression
• Calibration Sources
• Absolute emissivity
• Homogeneity

4
FPU Structure

• Most (but not all) of the FPU structure has been
  used in CQM
• Thermal requirements fulfilled by CQM as far as
  tested expect no changes with FM
• More detailed tests necessary w.r.t. sensitivity
  to L0/L1 interface temperature tolerances/variatio
  ns
• GeGa detector thermal interface changed for
  thermal curing
• LHe Optical Alignment Stability Test under way
• CQM ILT revealed no anomalies

5
Optics Mirrors

• All mirrors tested individually at ambient
  temperature
• Visible light end-to-end test
• Documentation with delivery of FPU
• No unexplained anomalies observed in QM
• But PSF measurements were hampered by telescope
  simulator defocus

6
Chopper

• Mirror optical performance
• Flatness lt 150 nm tested failed but accepted
• Roughness lt 50 nm tested passed
• Reflectivity gt 98 by verified coating process
• Actuator performance (static/dynamic)
• Range observation 4.1 accuracy 1
  arcmin tested ok
• Duty cycle observation _at_ 10 Hz gt80 tested ok
• Range calibration 9 accuracy 2
  arcmin tested ok
• Duty cycle calibration gt70 tested ok

7
Grating (I)

• Groove period - spec 117.65 ( 0.7) µm
• Only measured for CQM g117.66 0.11 µm (2
  sigma)
• Facet angles - spec 34.5 ( 1) and 62.4 ( 1)
• Average 34.1846 standard deviation 0.3455
• Average 62.3264 standard deviation 0.4233
• Groove regularity - spec 0.3 µm r.m.s.
• Not verified ? search for grating ghosts in ILT
  essential!
• Positioning precision of machine used for ruling
  is 0.1 µm w.r.t. reference (reference Heidenhain
  glass ruler). Measured ruler error
  (interferometric) over 100 mm travel0.15 µm
  (p-p) no measurement over full length available
• Groove depth - spec 56 µm 2 µm
• Not measured, but 0th order diffraction
  efficiency indicates no major deviation of
  grating profile from spec

8
Grating (II)

• Groove parallelism - spec 10
• Each groove to each other not verified, but hard
  to miss with machine used for ruling
• Grooves to rotation axis no absolute measurement
  done, but grating drive wobble measured uses up
  error entire budget!
• ?Thorough test of position shifts and spectral
  shear/tilt as function of grating angle during
  ILT required!
• Overall surface flatness - spec 3 (goal 1.5) µm
  r.m.s.
• Verification by WFE measurement with 10 µm
  interferometer in three grating orders partly
  achieved (only partial coverage of grating area
  by beam at a time) machining error lt0.5 µm (but
  internal stress in grating body could lead to
  deformation)
• ? Confirmation by measurement of PSF / spectral
  profile during ILT

9
Grating Drive

• Position precision within the useful angular
  throw 8 arcsec (goal 4 arcsec)
• Calibration certificate 3 arcsec 4 arcsec
  (nom. red.)
• Grating position jitter shall be lt 0.1
  arcsec/vHz
• verified by test
• Wavelength switching amplitude of lt 3 arcmin
  with frequencies of lt 3 Hz and a duty cycle of
  80
• verified by test
• Stabilization time for a grating step of 18
  arcseclt 23 ms
• verified by test

10
Filters Red Photometer
11
Filters Green Photometer
12
Filters Blue Photometer
13
Filters Red Spectrometer
14
Filters Green Spectrometer
15
Filters Blue Spectrometer
16
Calibration Sources

• No measurements of FM CSs possible before FM ILT
• Cause of inhomogeneity in CS1 illumination
  identified in QM FPU avoided in FM FPU
• Emissivity adjusted
• Stability expected in spec (similarity with QM)

QM
QM
CS1
CS2