NOTCam - an overview
NOTCam is a multi-mode instrument for use in the short-wave infrared (SWIR)
region of the electromagnetic spectrum (0.8 - 2.5µm). It is based
on the Rockwell Science Center "HAWAII" array with 1024×1024×18.5µm pixels in HgCdTe. NOTCam is capable of:
Wide field imaging (4'×4' @ 0.234"/pixel)
High resolution imaging (80"×80" @ 0.078"/pixel)
Low-resolution (R = 2500) WF-cam spectroscopy (Y,J,H,K)
Medium-resolution (R = 5500) HR-cam spectroscopy (J,H,K)
In the future we expect to upgrade NOTCam with Wollaston prisms for
imaging polarimetry and spectro-polarimetry.
On entering the front window of the dewar, light passes through the
following components before impinging on the detector
engineering grade array (SWIR1) ,
first science grade array (SWIR2) ,
new science grade array (SWIR3)
- the aperture wheel
- At the telescope focus, carries
and masks. There are 4×50-mm and 8×18-mm slots.
- the collimator
- the shutter
- A rigid spinning disk.
- two filter wheels
- Each with 16 slots of 25mm diameter allowing
for the use of up to 30
- the pupil wheel
- At a pupil plane, carries Lyot stops and other
masks. There are 16 slots.
- the grism wheel
elements. There are 16 slots. Check
- the lens wheel
- Carries two sets of imaging optics, one for
each plate scale (the WF and HR cameras), and the pupil re-imager.
Since NOTCam is kept cold for long periods at a time, we do not change
filters, slits, grisms etc. more often than absolutely necessary (see
the current setup).
The original optical design is described
here (postscript document).
This entire assembly is mounted on an optical bench which is in thermal
contact with an LN2 tank. Additional cooling is provided by
a pulse-tube refrigerator (PTR) from Iwatani. The optical bench is
covered with a radiation shield and this and the LN2 tank are
surrounded by a superinsulating blanket. The final enclosure is the dewar
skin which maintains a high-quality vacuum surrounding the instrument.
Mechanics and Cryogenics.
NOTCam will use a Copenhagen imaging array controller.
Instrument control software is written in IDL using the ALFOSC
model with a point-and-click interface. Programmer:
Temperature control and display has been made in Tcl/Tk together with a lower layer input/output control
program that also is used below the instrument control interface.
Detector control runs through a version of the Copenhagen
software BIAS. Programmer: Jens Klougart.
The NOTCam development team.