Subject: AOTF camera

From: Nancy Chanover

Submitted: Thu, 4 Feb 1999 13:12:23 -0700

Message number: 336 (previous: 335, next: 337 up: Index)

The GSFC AOTF instrument has been used on the APO 3.5-meter successfully
on several occasions during the past few years, as a visitor instrument
in collaboration with an ARC institution PI.  It provides narrow band,
tunable IR imaging capability and is described in detail below.

During a part of the coming quarter (2Q1999), the AOTF will be available to
a limited number of ARC users on an open (not necessarily collaborative) basis
using telescope time from institutional TACs or perhaps  DD time.  See below
for details and please be sure to consult with John Hillman or Nancy Chanover
before making an AOTF proposal.

Although no definite arrangements have yet been made, it is possible that
the AOTF will be made available to the APO 3.5-meter user community again
in the future.

Opportunity to use Goddard AOTF Camera on the 3.5 Meter

The Goddard near-IR AOTF camera will be available for limited use by
interested ARC members from the end of April 1999 to the end of
June 1999.  The AOTF camera has been successfully used at APO serveral
times over the past couple of years, and in the spirit of promoting new
instrumentation at APO, we are "testing the waters" to see if there is ARC
community interest in the possible future availability of the AOTF at APO,
be it occasional or semi-permanent.  An instrument description as well
as a discussion of logistical issues (PLEASE READ FIRST) follows.
Please contact the following people for more information:

John Hillman, GSFC PI
(301) 286-3630

Nancy Chanover, ARC PI
(505) 646-2567


-  Those interested in using the AOTF must be ON-SITE for the observations.

-  The instrument is not interfaced with REMARK, therefore all operations
occur from inside the dome.

-  The instrument must be operated under the supervision of either the
GSFC PI (Hillman), the ARC PI (Chanover), or one of their proxies.
Therefore any instrument proposing and subsequent scheduling must done
in coordination with them to ensure that someone can be at APO during
the proposed observing time.

-  Observing proposals will need to include GSFC(and/or NMSU) instrument
team member(s) as Co-Is, because the instrument operations require
their presence.


The GSFC near-IR acousto-optic tunable filter (AOTF) camera couples a
tunable filter with a near-IR focal plane array.  It was developed with
funds from NASA's Planetary Instrument Definition and Development Program,
and thus has been used heretofore to observe planets (Venus and Mars) with
the APO 3.5 meter telescope.  However, in principle it can be used for a
variety of astronomical applications.


Broadband randomly polarized light is incident on the AOTF, a TeO2 crystal,
and is separated into ordinary and extraordinary polarized components.
When RF acoustic waves are coupled into the crystal via a transducer, the
refractive index is spatially modulated, producing a phase grating that
diffracts one specific wavelength of the incident light. This light is
symmetrically deflected into 2 orthogonally polarized beams on exit from
the crystal, one of which is imaged by the focal plane array.  All other
wavelengths pass through the crystal undiffracted along the incident ray


FPA format: 256 x 256 pixels, 40 micron pixels, Rockwell PICNIC HgCdTe array
FPA wavelength range: 1.7 - 3.8 microns
Chip read noise: 30 electrons
Dark Current: 4 electrons/sec (78 K)
Focal ratio: f/10 (input), f/20 (at FPA)
Plate scale on APO 3.5 m: 0.13 arcsec/pixel, FOV ~ 33 arcsec
AOTF Bandpass: fixed in frequency space at 10.3 wavenumbers (cm^-1);
					R = 390 at 2.5 microns
AOTF spectral range: 1.7 - 3.4 microns
Instrumental throughput (telescope + camera optics + AOTF crystal):
     randomly polarized source: ~10-20%
     linearly polarized source: ~20-40%


The instrument has two basic modes of operation, which are enabled
by scriptable image acquisition software and synchronous control
of the RF source.  For spectral survey work, it is used as a
multi-spot scanning spectrometer by incrementing the AOTF wavelength
and synchronously measuring the pixels in multiple regions of interest,
while neglecting the rest of the scene.  Scan parameters such as
wavelength range, choice of wavelengths, step size and integration
time between steps are keyboard selectable.  In the imaging mode,
it operates as a full-format camera at each wavelength and can
acquire/store a complete spectral image cube at a pre-chosen set of
wavelengths.  Wavelength difference images (e.g., for producing images
in a spectral feature) can also be created by interlacing short
integrations at in-band and adjacent out-of-band wavelengths.

The chip has a 16-bit analog to digital converter, and the images are
stored in FITS format.


imaging spectrocopy
spectropolarimetry (polarization sensitivity limit ~ few %)


Chanover, N. J., D. A. Glenar, and J. J. Hillman (1998).  Multispectral
near-IR imaging of Venus nightside cloud features. J. Geophys. Res. 103,

Glenar, D. A., J. J. Hillman, B. Saif, and J. Bergstralh (1994).
Acousto-optic imaging spectropolarimetry for remote sensing.
Applied Optics 33, 7412-7424.

Glenar, D. A., J. J. Hillman, M. LeLouarn, R. Q. Fugate, and J. D.
Drummond (1997).  Multispectral imagery of Jupiter and Saturn using adaptive
optics and acousto-optic tuning.  Publ. Astron. Soc. Pacific 109,

Nancy Chanover                      phone: (505) 646-2567
Box 30001/MSC 4500                  FAX:   (505) 646-1602
New Mexico State University         email:
Las Cruces, NM 88003-0001

To find me: Astronomy Building, corner of Frenger and Williams, Rm 210

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