A narrow-band tunable solar filter for the near-infrared spectral region

A narrow-band tunable solar filter was constructed for the near-infrared spectral region. It is a pre-monochromator consisting of a double monochromator with dispersion subtraction, while the final passband is formed by a scanning Fabry-Perot interferometer. Such a filter can be realized in practice for any optical spectral region. The tuning range of the filter for the near-infrared is 9000-11 000 Angstrom, FWHM of the passband equals 0.24 Angstrom at the He I 10830 Angstrom line. The angular field of view on the sky is 3.6' for a diameter of the telescope of 100 mm. Filtergrams of the active region NOAA 8076 in the He I 10830 Angstrom line were obtained on 28 August 1997, the profiles of this line in the selected points of the image, and radial velocity field are presented.