25 August 1998 Conjugate Cassegrain telescopes for thermal source FTIR spectral radiometric calibration
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Abstract
Two Cassegrain telescopes were constructed to function as sender and receiver for an FTIR spectrometer primarily for the purpose of obtaining spectral data for analysis of military night vision emission targets, and spectral calibration of external variable temperature thermal radiation sources, utilizing freezing-point type blackbodies for primary radiation temperature standards. The sender and receiver telescopes, F/7 and F/5, respectively, each employ 0.30 m (12 in) diameter primary and 0.15 m (6 in) diameter secondary, protected Ag coated Zerodur mirrors. In operation, a thermal target image formed by the sender, whose optical axis is aligned with that of the receiver and spectrometer, is transmitted to and brought to a focus at the spectrometer entrance aperture by the receiver telescope. With (lambda) /8 p-v optical surface accuracy at 633 nm, telescope system tests indicate near diffraction- limited performance in the visible, and 2.81 mrad (full) FOV with further reduction achieved with field stops. Wavelength range capability of the commercially available FTIR instrument employed is approximately 0.22 micrometers (55000 cm-1) to 22 micrometers (450 cm-1) with wavenumber resolution of about 0.013 cm-1 in the IR to 0.769 micrometers (13000 cm-1). In this paper, the techniques and tests employed for the telescope mirror construction are described. An innovative technique for secondary alignment for Hindle's tests of a Cassegrain utilizing a He-Ne laser is presented. Telescope mountings for positioning and alignment with the FTIR are briefly discussed, as well as radiometric and calibration parameters for the integrated system.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Martin Wolk, Robert J. McGillicuddy, Joseph E. Zurlinden, "Conjugate Cassegrain telescopes for thermal source FTIR spectral radiometric calibration", Proc. SPIE 3352, Advanced Technology Optical/IR Telescopes VI, (25 August 1998); doi: 10.1117/12.319307; https://doi.org/10.1117/12.319307
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