Telescope optics correct atmospheric dispersion

In addition to the use of adaptive optics to correct for chromatic path-length and displacement errors in extremely large telescopes (ELTs), researchers at the National University of Ireland (Galway, Ireland) have developed a linear atmospheric-dispersion corrector (ADC) intended to be coupled with a deformable mirror on a 42-m-diameter ELT, that corrects for a third major atmospheric effect known as angular atmospheric dispersion.

In addition to the use of adaptive optics to correct for chromatic path-length and displacement errors in extremely large telescopes (ELTs), researchers at the National University of Ireland (Galway, Ireland) have developed a linear atmospheric-dispersion corrector (ADC) intended to be coupled with a deformable mirror on a 42-m-diameter ELT, that corrects for a third major atmospheric effect known as angular atmospheric dispersion. Also called differential refraction, angular atmospheric dispersion is defined as the dependence of the apparent position of an astronomical object on wavelength as a result of atmospheric temperature, pressure, and relative-humidity changes.

The ADC consists of two optical wedges of F5 glass with a central thickness of 40 mm and diameters of 0.75 and 0.72 m. Because the amount of dispersion introduced by the ADC is proportional to the axial distance between the two wedges, it is possible to translate one of the wedges along the optical axis and compensate for angular atmospheric dispersion. When the ADC is used along with a deformable mirror to correct for intrinsic aberrations introduced by the ADC optical wedges, diffraction-limited image quality is possible over a 1 arcmin field. Contact Alexander Goncharov at alexander.goncharov@nuigalway.ie.

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