SAFARI INSTRUMENT (IN ASTROPHYSICS)

SAFARI Instrument

SAFARI Instrument

SpicA FAR-infrared Instrument (SAFARI) Imaging Spectrometer

The baseline optical configuration of this European instrument is a Mach-Zehnder imaging Fourier Transform Spectrometer (FTS). The principal advantages of this type of spectrometer for ESI are the high mapping speed of the FTS due to spatial multiplexing, the ability to incorporate straightforwardly a photometric imaging mode and the operational flexibility to tailor the spectral resolution of the science programme. The detector technology candidates of the insturment are Si:Sb and Ge:Ga photoconductors, transition edge sensor (TES) bolometers and kinetic inductance detectors (KIDs).

SAFARI will cover the FIR window that extends from ~30 µm (the upper cut-off of the MIR instruments) to ~210 µm (just long ward of the [NII] 206 fine structure line) with a field-of-view of 2'x2'. Assuming diffraction limited performance, SAFARI will provide angular resolutions from ~2" to 15" (20 to 150 AU at 10 pc) at wavelengths not covered by JWST and at more than 2 orders of magnitude higher sensitivity than Herschel/PACS. This huge increase in sensitivity could potentially open EP research to wavelengths completely blocked by the Earth's atmosphere, but representing the emission peak of many cool bodies (gas-giant planets, asteroids and so on). SAFARI will have its major strength in measuring excess radiation from dusty proto-planetary disks in hundreds of stars at almost all galactic distances. It will also perform medium spectral resolution observations (R~2,000) over a spectral range also rich in dust features, water vapour rotational lines (temperatures below ~500 K), atomic oxygen fine structure lines at ~63 µm and the solid state water-ice features at ~44 and ~62 µm.

Mid-Infrared Coronagraph

The Coronagraph instrument is used to carry out high contrast observations by suppressing the side lobes of the point spread function (PSF) of a bright source (i.e. a star) enabling observation of companion objects (e.g., planets and proto-planetary disks).

Coronagraph's wavelength range is 5-27 µm with a possible extension to 3.5-5 µm. The instrument has two observation modes; imaging and R~200 spectroscopy. The contrast requirement is 106 to detect exoplanets directly in the MIR. Realising such high contrast is very challenging and we plan to develop two coronagraph methods. The first uses a binary shaped pupil coronagraph, which is regarded as the most simple and robust approach. Laboratory demonstrations of this method have already been successfully done with visible light and a 107 contrast has been confirmed in the experiment. The second method uses a hybrid technique of phase induced amplitude apodisation (PIAA) and binary shaped pupil. The advantage of the hybrid solution over the shaped pupil method is that the inner working angle (IWA) is reduced from ~ 3.5 ?/D to < 2 ?/D. Another advantage of the hybrid solution is an improvement in throughput from ~30% for the shaped pupil only method to ~ 80% for the hybrid method. Although the hybrid solution requires more complicated optics than the shaped pupil mask only method, a contrast better than 106 has been experimentally demonstrated with visible ...