Single-component reflecting objective for low-temperature spectroscopy in the entire visible region.

A single-component reflecting objective was constructed for low-temperature spectroscopy with optimal imaging and transmission properties at all visible wavelengths. The performance of the objective immersed in superfluid helium at a temperature of 1.5 K was tested by comparing dark-field images of uncolored polymer beads taken at wavelengths of 400 and 800 nm. Under conditions optimized for imaging at both wavelengths, the size of the image is <1.3 times of the diffraction limit. The objective collects emission from a point source at focus with a solid angle of 0.32π sr. [ABSTRACT FROM AUTHOR]