Spectral imagery with an acousto-optic tunable filter

Abstract

We have fabricated a spectral imager for astronomy and aeronomy using collinear or noncollinear acousto-optic tunable filters (AOTFs). The AOTF provides high transparency, rapid tunability over a wide wavelength range, a capability of varying the bandwidth by more than an order of magnitude, high etendué, and linearly polarized output. We demonstrate here some typical observational applications of acousto-optic tunable filters used in several configurations at astronomical telescopes.

THE SEARCH FOR PLANETARY MASS COMPANIONS TO FIELD BROWN DWARFS WITHHST/NICMOS

“…Because of the higher achievable contrast and the lack of suitable AO reference stars, the observations were conducted from space with HST as explained in the following. The observing strategy that suited best to reach our goal of detecting planetary mass objects around brown dwarfs and to overcome the remaining brightness contrast, was the spectral differential imaging (SDI) technique (Smith et al 1987). This technique takes advantage of the fact that a cool (≤ 1300 K) giant planet or low-mass brown dwarf (i. e. T dwarf) is much fainter in certain molecular bands due to strong absorption than in the neighboring continuum.…”

The Development and Demonstration of the Portable Acousto‐Optic Spectrometer for Astrobiology in Cave Environments

“…AOTF devices have been used for multispectral or hyperspectral imaging for several decades (N. J. Chanover et al, 1998Chanover et al, , 2003Glenar et al, 1994Glenar et al, , 1997Smith et al, 1987), but only in more recent years have they been incorporated as elements of spectrometers used for planetary flight projects (Agrawal et al, 2015;Bertaux et al, 2007;Bibring et al, 2017;O. Korablev et al, 2006;O.…”

“…The unique aspect of PASA that sets it apart from standard reflectance spectrometers is the use of an AOTF for the wavelength selection element. AOTF devices have been used for multispectral or hyperspectral imaging for several decades (N. J. Chanover et al., 1998 , 2003 ; Glenar et al., 1994 , 1997 ; Smith et al., 1987 ), but only in more recent years have they been incorporated as elements of spectrometers used for planetary flight projects (Agrawal et al., 2015 ; Bertaux et al., 2007 ; Bibring et al., 2017 ; O. Korablev et al., 2006 ; O. I. Korablev et al., 2018 ). AOTFs are recognized as a low power, low mass, radiation tolerant option for space flight, thus they are a suitable technology for a spectrometer intended for operation on a lander or rover platform.…”

“…AOTFs can be made from one of several birefringent materials, including crystalline quartz, magnesium fluoride, sapphire, thallium‐arsenic‐selenium, and tellurium dioxide (TeO 2 ). Tellurium dioxide has the widest operating wavelength range of ∼0.4 to nearly 5 μm (Smith et al., 1987 ), and consequently it is the most commonly used for AOTF devices.…”