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 John.Hillman@gsfc.nasa.gov (301) 286-3630 Nancy Chanover, ARC PI nchanove@nmsu.edu (505) 646-2567 LOGISTICAL ISSUES - 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. INSTRUMENT DESCRIPTION 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. HOW IT WORKS 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 direction. INSTRUMENT SPECS 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% DATA INFORMATION 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. POSSIBLE ASTRONOMICAL APPLICATIONS imaging spectrocopy spectropolarimetry (polarization sensitivity limit ~ few %) RELEVANT REFEREED PUBLICATIONS Chanover, N. J., D. A. Glenar, and J. J. Hillman (1998). Multispectral near-IR imaging of Venus nightside cloud features. J. Geophys. Res. 103, 31,335-31,348. 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, 326-337. ********************************************************************** Nancy Chanover phone: (505) 646-2567 Box 30001/MSC 4500 FAX: (505) 646-1602 New Mexico State University email: nchanove@nmsu.edu Las Cruces, NM 88003-0001 To find me: Astronomy Building, corner of Frenger and Williams, Rm 210 ********************************************************************** APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 336 in the apo35-general archive. 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