The SAFARI instrument (current) baseline concept

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Instrument requirements/specifications

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Field of view 2' x 2‘ (close to) Nyquist sampled

modes:

photometry / ~ 3

SED mode / ~ 150 - 200

spectroscopy / ~ 2000

line sensitivity few x 10-19 W/√Hz (5σ-1h)

continuum sens. <20 Jy (5σ-1hr)

bright sources up to 1 Jy without ND filter

3 bands:

SW, 34-60 µm 43x43

MW, 60-110 µm 34x34

LW, 110-210 µm 18x18

The SAFARI instrument - summary

• Scanning Fourier Transform Spectrometer with 2’x2’ FoV

• Simultaneously observing in 3 bands (34-210m)

• Ultra sensitive TES detectors/SQUID read out at 50 mK

almost 200 times more sensitive than Herschel

• Frequency Domain Multiplexing

• To be built by an SRON-led consortium

• ~15 institutes in Europe, Canada, Japan - cost ~170M€

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PHASE A

ROOFTOP Front

optics

Detect

or box

Main body

frame

2 light tight

covers

…a complex instrument result of many design iterations

Scanning FTS

output port 1

BS2 BS1

calibrator

sky input

output port 2

The Mach-Zehnder interferometer

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S(σ)

RS(σ)

TS(σ)

RS(σ,p)

R2 S(σ) +T2 S(σ)

{1+cos(2pσ)}

2RT S(σ)

{1+cos(2pσ)}

The basic Mach-Zehnder interferometer in motion

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FFT

Instrument toplevel

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Telescope

Focal plane optics:

mirrors, filters, FTS, detectors

Amplifier

Detector read-out and control

Instrument control

Reference design - SAFARI Focal Plane Unit

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Filter wheel FTSM

Mach-Zehnder interferometer

4K-shield around detector box and FPA’s

Input Optics Module with Pick-off-Mirror

Detector filters - SW

The SAFARI imaging spectrometer - Italian SPICA workshop

Focal Plane Assembly

Detector filters – LW/MW 50mK cooler

Shutter

Filter wheel

Calibration source FTSM

SAFARI FPU mechanisms

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FTSM

50mK cooler

SAFARI’s ultimate sensitivity: Transition Edge Sensors

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Ultimate sensitivity – Transition Edge Sensors

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• Phonon-noise NEP~T√G Challenges: • ~milli-K environment • Very sensitive to E/B fields • Small pixels (480 μm) and low G trying layout with ‘long thin legs’

Bolometer

G

TESTES

Ta absorberTa absorber SiSixxNNyy legslegs

TESTES

Ta absorberTa absorber SiSixxNNyy legslegs

- G Temperature (~50 milli-K)

Resis

tance

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Prototype: 8x9 S-band arrays on 250 nm SiN

• 100 % yield, Tc=105 mK (~ 2 %) • NEP=5-6 x10-19 W/√Hz • Varying saturation level

Manufactured to date: 38 x 38 array (M-band) 20 x 20 array (S-band)

Sensitivity reached to date: NEP=5-6 x10-19 W/√Hz

The SAFARI imaging spectrometer - Italian SPICA workshop

Detector system - Focal Plane Assemblies

• Unit to hold TES’s + LC filters + SQUID’s

• One FPA per detector array

• Isolate temperature levels: 50mK/300mK/1.7K

• Shielding: quasi-static B-fields, radiated EMI, stray light

• Challenges

• Multiple functions volume/mass constraints

• High launch loads

• Compact, light-weight B-shield

• Harness for upto ~2000 pixels

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