PACS SVR 2 18 Jan 2007 FM ILT: Spectrometer1 Spectrometer Performance H. Feuchtgruber, T. Müller, A. Poglitsch

FM ILT: Spectrometer

PACS SVR 2 18 Jan 2007

1

Spectrometer Performance

H. Feuchtgruber, T. Müller,A. Poglitsch



2

Overview

• Thermal behaviour • Spectral coverage• Wavelength calibration• Spectral resolution and instrumental profile• Sensitivity NEP• Relative spectral response• Leakage and Ghosts• Photoconductor Arrays

!! Mostly draft results, no final reports yet !!



3

Boundary Conditions

• Limited Time

• Apply best guess values for detector biases and heater

• Measurements have been carried out in few flux regimes

with mostly smallest capacitor.

• Optics misaligment and the significant amount of time

spent to investigate it

• Blue and Red spectrometer had to be operated separately



4

Thermal Behaviour (1)• Results from CUS Observation: “SPEC_thermal_OBS”

• Test of all spectroscopy components within one single measurement• Illustrate the temperature behaviour of PACS during typical spectrometer and photometer operations• Determine FPU temperature upper limits during heat dissipation• Measure temperature transients in the individual sub-units• Assess overall thermal conductances and heat fluxes• Verify proper thermal strapping to cryostat thermal reservoirs• Identify possible problem areas



5

Thermal Behaviour (2)• Results from CUS Observation: “SPEC_thermal_OBS”

• Test of all spectroscopy components within one single measurement• Illustrate the temperature behaviour of PACS during typical spectrometer and photometer operations• Determine FPU temperature upper limits during heat dissipation• Measure temperature transients in the individual sub-units• Assess overall thermal conductances and heat fluxes• Verify proper thermal strapping to cryostat thermal reservoirs• Identify possible problem areas



6

Spectral coverage

Available grating range = 44.62 degrees working range = 43.1 degrees (low grating output)

order “measured” specification [45000 – 1050000]

n=3 73.2µm – 34.8 µm 72µm - 56µm n=2 109.8µm – 52.2µm* 105µm - 72µm n=1 219.6µm – 104.3µm 210µm - 105µm

* Nominal 72-56µm band can be measured in grating order 2 and 3



7

Wavelength Calibration (1) Sources and available measurements:

- FIR-Methanol-Laser provided by LENS Tested spectral lines: 70.512, 77.406, 96.522, 118.834 µm - OGSE vapor cell Tested spectral range scans: 58-60µm and 132-145µm

=; =; gLHe=117.175; n=[1,2,3] ; pix=[1..16]

=0-gratpos/dgrat with dgrat=23301[steps/]

So far just: 0 (FM) = 0 (CQM) + 3.78 (no detailed analysis and no

module dependence yet !)



8

Wavelength Calibration (2)

Laser: 70.512 µmGrating order = 3Filter A

Pixel:11,7

Laser setup in front of cryostat



9


Laser: 70.512 µmGrating order = 3Filter A

Pixel:11,7

Signals beyond cut level in white

MeasuredGaussfit



10


Blue spectrometer,Grating order 3, single pixelVapor cell p = 20-28mbar

Red spectrometer,grating order 1,single pixelVapor cell p = 8.5 mbar

MeasuredModel

MeasuredModel



11

Spectral Resolution & Instrumental Profile

• 3 laser lines confirm predictions from design on central pixels • Instrumental profile is “gaussian” at least down to a residue at 3% level



12

• Staring measurement at fixed grating position and given OGSE BB input flux has been analyzed (no dark current and straylight considerations yet !):

• CRE setting: Nominal bias, smallest capacitor, 64 readouts per ramp

Sensitivity: System NEP Map

blue red

88µm; TBB=30K; Ppix=3.96e-14W 194µm; TBB=22.5K; Ppix=1.15e-14W



13

Relative Spectral Response

n=3

n=2

n=2

n=1

BB@12KCint=140fF

BB@30KCint=230fF

• Draft analysis of different spectral scans on OGSE BB at 30K.

• Single pixel only

• Probably saturation effects for red detector at 30K

• Leakage effects seen at longwave band edges

Not yet measured with n=1

57µm 105µm72µm

leakage



14

Leakage and Ghosts (1)



15




16

- Plot of Ghost Responses in 1st Order

0th

order

Leak 2nd order

Ghost 2nd order 2pass

Ghost 1st order 2passNormal Signal

Ghost 1st order 3pass

From

SV

R 1



17

- Plot of Ghosts, 1st Order, with Baffles

Leak 2nd orderGhost 2nd order 2pass

Ghost 1st order 2passNormal Signal

From

SV

R 1



18


CQM “ghosts”

“clean” FM

• Successful baffling implemented



19

- Leakage effects are within expectations from order sorting filter performances

- ECR-011, baffle modifications were successful in removing the sharp spectral ghosts seen during CQM

- Tests with the strongest laser line at 118.834 µm did not show leaking features in the blue bands

- No ghosts seen during all laser tests




20

Photoconductor Arrays (1)

• PACS-ME-NCR-236: “2 pixels low response”

• PACS-ME-NCR-237: “crosstalk in supply group 2”



21

Photoconductor Array (2)• PACS-ME-NCR-237: “crosstalk in supply group 2” (few x 100mV/s up to several V/s)

• Crosstalk is also present in supply group 1, however much less (few x 10mV/s)

Measured“Model”

Dummy resistor !

Documents

PACS SVR 2 18 Jan 2007 FM ILT: Spectrometer1 Spectrometer Performance H. Feuchtgruber, T. Müller, A. Poglitsch