A monochromatic analysis of the RX nonimaging concentrators as imaging optical systems is presented (R stands for refractive, X for reflective). All of them have rotational symmetry and an image-side numerical aperture of 1.46 with the use of an index of refraction which means a half-rim angle of illumination of 77 deg. This is equivalent to 95% of the theoretical limit of concentration. For an object-side focal length of (i.e., an entry aperture diameter of 50 mm) and a wavelength the RX has an equivalent passband above in a field of view of and above in a field of view of This feature of RX concentrators allows one to use the same RX with receivers/emitters very different from the one of the design presented (in size and contour shape) with no loss of nonimaging quality. Moreover, the combination of simplicity, compactness, imaging capability, and high concentration makes the RX an exceptionally good optical device for high-sensitivity focal plane array applications.
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