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Session 9 - SOFIA and IR Instrumentation.
Display session, Wednesday, January 07
Exhibit Hall,

[9.08] Advanced Fabry-Perot Interferometers for Infrared Astronomy

L. Lesyna, R. Ryan, W. Van Nostrand, N. Fonneland, Y. Ng (Northrop Grumman), M. A. Greenhouse, S. Satyapal, J. Schepis (NASA/GSFC)

Fabry-Perot interferometers (FPI) enable imaging spectroscopy for astronomical applications that require spatial multiplexing over a wide field of view. For these purposes, FPIs achieve more than two orders of magnitude higher flux gathering power than grating spectrometers of similar size and resolution. FPIs offer unique advantages to other high geometric throughput systems such as Fourier transform spectrometers. In addition, FPIs can be combined naturally with grisms or gratings to satisfy mission requirements for both spectral and spatial multiplexing in a single instrument package. Such combinations show excellent promise for satisfying science requirements for future missions such as the Next Generation Space Telescope (NGST). A key technology development area is space flight qualifiable scanning etalon mechanisms for use in the 1 - 20 \mu m region.

Spectroscopy of galaxies and interstellar dust require moderate spectral resolution ( \lambda / \Delta \lambda \verb+ + 10^2 - 10^3). FPIs can achieve this range with high transmittance by extending their operation to low orders of interference (n<3). Our etalon actuator enables tuning over a wide range of gap lengths for rapid selection between high and low resolution imaging.

We have constructed and tested advanced FPIs operating at wavelengths in the 3 - 5 \mu m and 8 - 12 \mu m bands. Dielectic multilayers were deposited onto zinc selenide substrates over a clear aperture of 25 mm, achieving 95% reflectivity for the 3 - 5 \mu m band and 98% reflectivity for the 8 - 12 \mu m band. Low order operation necessitates control of the phase shift upon relection; to achieve the widest scanning range we designed and fabricated minimum phase dispersion coatings. In first order, both mirror sets exhibited a free spectral range exceeding the band of interest.

We use closed-loop capacitance micrometry to control substrate separation and parallelism with a digital signal processing based personal computer control system. Piezoelectric translators are used to provide fine motion control; inchworm actuators provide gross motion. This hybrid gross/fine motion system has demonstrated operation over a wide range of spectral resolutions with good transmission efficiency. We are currently modifying these actuators for cryogenic operation.

We will present laboratory performance data and discuss potential applications.

Program listing for Wednesday