PACS FPU Subunits 1

PACS SVR 22/23 June 2006

FM FPU Subunits

A. Poglitsch

PACS FPU Subunits 2

PACS SVR 22/23 June 2006

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)

PACS FPU Subunits 3

PACS SVR 22/23 June 2006

Performance of FPU and Subunits (II)

• Filters– In-band transmission– Out-of-band suppression

• Calibration Sources– Absolute emissivity– Homogeneity

PACS FPU Subunits 4

PACS SVR 22/23 June 2006

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/variations– Ge:Ga detector thermal interface changed for

thermal curing

• LHe Optical Alignment Stability Test under way– CQM ILT revealed no anomalies

PACS FPU Subunits 5

PACS SVR 22/23 June 2006

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

PACS FPU Subunits 6

PACS SVR 22/23 June 2006

Chopper

• Mirror optical performance– Flatness < 150 nm tested; failed but

accepted– Roughness < 50 nm tested; passed – Reflectivity > 98% by verified coating process

• Actuator performance (static/dynamic)– Range observation ± 4.1°; accuracy ± 1 arcmin tested;

ok– Duty cycle observation @ 10 Hz >80% tested;

ok– Range calibration ± 9°; accuracy ± 2 arcmin tested;

ok– Duty cycle calibration >70% tested; ok± 0.5 arcsec on sky

PACS FPU Subunits 7

PACS SVR 22/23 June 2006

Grating (I)

• Groove period - spec 117.65 (± 0.7) µm– Only measured for CQM: g=117.66 ± 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 travel:0.15 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

PACS FPU Subunits 8

PACS SVR 22/23 June 2006

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 <0.5 µm (but internal stress in grating body could lead to deformation)

Confirmation by measurement of PSF / spectral profile during ILT

PACS FPU Subunits 9

PACS SVR 22/23 June 2006

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 < 0.1 arcsec/√Hz– verified by test

• Wavelength switching: amplitude of < 3 arcmin with frequencies of < 3 Hz and a duty cycle of 80%– verified by test

• Stabilization time for a grating step of 18 arcsec:< 23 ms– verified by test

PACS FPU Subunits 10

PACS SVR 22/23 June 2006

Filters: “Red” Photometer

PACS FPU Subunits 11

PACS SVR 22/23 June 2006

Filters: “Green” Photometer

PACS FPU Subunits 12

PACS SVR 22/23 June 2006

Filters: “Blue” Photometer

PACS FPU Subunits 13

PACS SVR 22/23 June 2006

Filters: “Red” Spectrometer

PACS FPU Subunits 14

PACS SVR 22/23 June 2006

Filters: “Green” Spectrometer

PACS FPU Subunits 15

PACS SVR 22/23 June 2006

Filters: “Blue” Spectrometer

PACS FPU Subunits 16

PACS SVR 22/23 June 2006

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 CS1CS2