Achromatic Catadioptric Microscope Objective in Deep Ultraviolet with Long Working Distance

We present a microscope imaging optics system that is suitable for simultaneously detecting two species of electrically trapped atomic ions for quantum information processing. The proposed 10x objective features all-spherical surfaces in a catadioptric modification of the Schwarzschild two-mirror configuration and is achromatic at 313 and 280 nm, the two wavelengths of the laser-induced fluorescence from 9Be+ and 24Mg+. To correct for aberrations from the fused-silica vacuum window, we use a zero-power doublet made of a positive calcium fluoride and a negative fused-silica meniscus to form an air-gapped Steinheil doublet facing the object. As a result, diffraction limited images are obtained for both wavelengths at a numerical aperture (NA) of 0.5 and a field of view (FOV) of 0.1 mm in diameter. The long working distance (> focal length) of this objective allows imaging of the ions through the vacuum window.