We have developed an objective for ultraviolet imaging and spectroscopy under cryogenic conditions. The objective was made of a single piece of silica with two spherical mirror surfaces. The pair of mirrors works as a reflecting objective for the optical rays that travel inside the silica. The extra refraction at liquid helium–silica interfaces was found to cause practically no chromatic aberration in the wavelength region from 360 to 980 nm. Using the objective with a focal length of 2 mm and a numerical aperture of 0.6, imaging an area of is possible with almost diffraction-limited quality.
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