G. Dall'Oglio

Polarization properties of Fluorogold∗ in the far-infrared☆

Abstract Fluorogold, a glass-filled teflon, is widely used as a long-wave pass filter in the infrared. We have found an important intrinsic polarization arising from the scattering of the radiation by the aligned grains of the reinforcing aggregate bound by teflon. The effect must be taken into account in the case of Fluorogold filters employed with a polarizing Michelson interferometer for measurements of absolute fluxes, as in the course of observations of the cosmic background spectrum carried out by several authors.

Observations of cosmic background radiation anisotropy from Antarctica

A ground-based experiment has been carried out in Terra Nova Bay, Antarctica in order to detect anisotropies in cosmic background radiation at an angular scale of 1.3 deg. A 1-m-diameter flux collector and an He-3-cooled bolometric detector sensitive to radiation with a wavelength between 1.86 and 2.34 mm are used. Observations were carried out during the Antarctic summer and are limited by atmospheric emission fluctuations. 13 references.

Evidence for polarised radiation from the Sun in the far infrared.

Abstract During a balloon borne experiment intended to study the state of polarization of the far infrared radiation in the 100–2000 micron range, a signal was detected from the Sun corresponding to a linear polarization of at least 6,4 % assuming a constant polarization over the whole infrared bandwidth observed (wavelengths longer than 500 microns cannot contribute significantly to the observed signal even if they are completely polarized). The vibrational plane is parallel to the Sun equator within 5°.

Atmospheric transmission and noise measurements in Antarctica

Abstract We describe a set of measurements carried out in Antarctica during the second Italian Antarctic Expedition. Atmospheric precipitable water vapour, millimetric transmission and noise were monitored for 2 months during the austral summer. The results suggest that the site is favourable for far infrared astronomy measurements.

Narrow band filters for astronomical applications in the far infrared

Abstract Interference filters adequate to isolate the atmospheric windows in the 30-5 cm −1 spectral region are described. The filters have a half-bandwidth of about 2 cm −1 and, with suitable blocking, a rejection factor larger than 10 8 is obtained up to the visible region.

Comparison between carbon, silicon and germanium bolometers and Golay cell in the far infrared

Abstract Different kinds of far i.r. bolometers are compared between 100 and 5 cm−1 in various optical arrangements. A Golay cell has been used as reference detector. The germanium bolometer seems to be about ten-times more sensitive than the other two detectors, while the carbon bolometer shows the highest responsivity.

Non-polarizing far-infrared filters

Abstract Polyethylene embedded with glass microspheres has shown the same optical properties as Fluorogold™ in the far-infrared. The polarizing properties of Fluorogold (laminated in thin foils) are avoided by pressing the polyethylene/glass powder between hot plates. The new fiters are suitable for long-wave pass filters with intrinsic polarization less than 10−4

Further evidence for polarized radiation from the sun in the far infrared

Abstract The polarization of the Suns radiation has been measured in the 30-10 cm −1 spectral region through the atmospheric windows at the high altitude observatory of Testa Grigia, Italy, at 3500 m a.s.l. The results are in agreement with those previously obtained during a balloon flight in the 100-5 cm −1 region. The spectral dependence of the linearly polarized component has been investigated and a possible interpretation of the obtained data is suggested.

Limitations of ground based near and far infrared astronomy

Abstract The possibilities of ground based infrared astronomy are discussed. It is shown that telescopes used up to now are not optimized and that the Diffraction Limited Detectivity conditions (DLD) cannot be reached, in the near infrared, by the larger telescopes. The maximum useful diameters for near i.r. and far i.r. telescopes have been evaluated and a new parameter (i.e. visibility) is introduced in order to describe the performances of i.r. ground based telescopes.

Atmospheric windows and broad band photometry in far infrared astronomy

Abstract The far infrared atmospheric windows between 30 cm −1 and 5 cm −1 have been investigated during many months of observations at the Alpine Station of Testa Grigia (3500 m a.s.l.). The seasonal and diurnal variation of the atmospheric transmittance for each window have been measured. The contribution of the minor atmospheric components is also discussed.