A beamsplitter includes a substrate formed from a material transparent to wavelengths of light at least above a selected cutoff wavelength and reflective structures distributed across a surface of the substrate. The reflective structures split incident light having wavelengths above the selected cutoff wavelength into a reflected beam formed from portions of the incident light reflected from the reflective structures and a transmitted beam formed from portions of the incident light transmitted through the substrate. A splitting ratio of a power of the reflected beam to a power of the transmitted beam is based on a ratio of surface area of the reflective surfaces to an area of the incident light on the substrate. Separation distances between neighboring reflective structures are smaller than the cutoff wavelength such that diffracted power of the incident light having wavelengths above the selected cutoff wavelength is maintained below a selected tolerance.