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Science ready Capabilities (Can be used from S14B onwards):

The SCExAO instrument is continuously growing and is therefore being commissioned in phases. As of January 2014 only phase I engineering has been completed and therefore only the modes tested within that phase can be used for science. These include the following:

  • Coronagraphs: The SCExAO instrument is equipped with several coronagraphs, which operate across the near-IR (y-K bands). Those that can be used include the Phase induced amplitude apodisation (PIAA), Vector Vortex, Four-Quadrant Phase Mask and Shaped pupil versions.

  • Tip/tilt (low order) control: The low order wavefront sensor (LOWFS) uses the rejected light from the coronagraphs in the near-IR to fine-tune the tip/tilt for optimum starlight rejection.

  • Coherent differential imaging: The speckle nulling routine allows for quasi-static speckles due to aberrations in the optics, or diffraction from the spiders and obstructions to be systematically beaten down. The performance of this mode is limited by the current generation of cameras (See below).

  • High frame rate imaging: The internal near-IR camera in SCExAO can run at up to 346 Hz offering the possibility to collect fast frames for lucky imaging or advanced PSF calibration of long exposures taken with HiCIAO.

  • Deep exposure imaging: HiCIAO is used to take longer exposures of a given target once it has passed through SCExAO. It can be used in conjunction with all the other modes described above or separate to them.

Please note SCExAO is a booster stage for the initial AO correction provided by AO188. In good seeing AO188 offers 20-40% Strehl ratios in the H-band. Please use this value when preparing proposals.

Coronagraphs

Coronagraph type PIAA Vortex 4QPM Shaped pupil
Inner working angle (λ/D) 1.5 1 1 3
Waveband(s) y-K H H y-K

Cameras

Speckle nulling is performed with the camera used for high frame rate imaging. This camera is the same as the one used for the LOWFS. They are both Axiom Optics OWL SW1.7HS units, which have an InGaAs CMOS array with 320x256 pixels that are 30x30 μm in size. These cameras can run full frame at 346 Hz and have a read noise of 115 and 140 e- respectively. The dark current is such that the maximum exposure is ~5-10 s. Please note that the speckle nulling routine operates on the speckles which are ~1000 x fainter than the central PSF and hence this must be taken into consideration when selecting your target, in light of the noise characteristics. The high frame rate/speckle nulling camera has a plate scale of 10.76 mas/pixel and a maximum field-of-view of 3.4"x 2.7". Please refer to the HiCIAO page for information on that camera. The plate scale of HiCIAO when used in conjunction with SCExAO is preserved. The high frame rate/speckle nulling camera can be used with a series of bandpass filters which include: y-band, J-band, H-band and 50 nm bandwidth centered at 1650 nm.

Pulpit rock Pulpit rock Pulpit rock

(Left) High frame rate science camera/speckle nulling camera. Mounted on a long translation stage to move between
the focal and pupil planes. (Middle) LOWFS camera. (Right) HiCIAO camera.

Calibration source

The internal calibration source consists of a Fianium super continuum source and 2 laser diodes centered at 650 and 1550 nm. The light from the source is delivered via an endlessely single-mode fiber to the bench ensuring a diffraction-limited calibration PSF from the visible to K-band. The brightness and spectral bands of the injected light can be easily controlled. In addition there is a turbulence simulator that can be used for realistic simulations of on-sky performance in the laboratory.

Pulpit rock Pulpit rock Pulpit rock

(Left) Internal calibration source unit (a.k.a rainbow maker). (Middle) Super continuum laser source attached to source box. (Right) Internals of
calibration source box. There is a shutter to turn the light on/off, and three wheels to control the ND in the vis/IR and spectral content.

For more technical details please refer to the publications page.

2014