Dedicated to Professor Dr. K. W. BOER on the occasion of his 70th birthday Thermal infrared sensors with maximal sensitivity and minimal response time require radiation absorbing layers with small heat capacity and high absorbance. In the near infrared these conditions are well met by black gold layers. In order to examine the question whether black gold layers are suitable absorbers as well in the far infrared, their reflectance is measured in a wave number range from k = 14 to 650 cm-', corresponding to a range in wavelength 1 = l / k between 15 and 710 pm.The samples are prepared at various residual gas pressures. The influence of tempering o m the absorbance and the spectral absorption behavior at low temperatures is discussed. The experimental results may be accounted for by a dielectric function according to the Bergman formalism. The spectral dependence of the absorption coefficient and the real and imaginary parts of the refractive index following from it are presented.
The Cassini spacecraft orbiting Saturn carries the composite infrared spectrometer (CIRS) designed to study thermal emission from Saturn and its rings and moons. CIRS, a Fourier transform spectrometer, is an indispensable part of the payload providing unique measurements and important synergies with the other instruments. It takes full advantage of Cassini's 13-year-long mission and surpasses the capabilities of previous spectrometers on Voyager 1 and 2. The instrument, consisting of two interferometers sharing a telescope and a scan mechanism, covers over a factor of 100 in wavelength in the mid and far infrared. It is used to study temperature, composition, structure, and dynamics of the atmospheres of Jupiter, Saturn, and Titan, the rings of Saturn, and surfaces of the icy moons. CIRS has returned a large volume of scientific results, the culmination of over 30 years of instrument development, operation, data calibration, and analysis. As Cassini and CIRS reach the end of their mission in 2017, we expect that archived spectra will be used by scientists for many years to come.
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