  Lightweight parabolic mirrors for solar concentrators have been fabricated
using carbon fiber reinforced polymer (CFRP) and a nanometer scale optical
surface smoothing technique. The smoothing technique improved the surface
roughness of the CFRP surface from ~3 {\mu}m root mean square (RMS) for as-cast
to ~5 nm RMS after smoothing. The surfaces were then coated with metal, which
retained the sub-wavelength surface roughness, to produce a high-quality
specular reflector. The mirrors were tested in an 11x geometrical concentrator
configuration and achieved an optical efficiency of 78% under an AM0 solar
simulator. With further development, lightweight CFRP mirrors will enable
dramatic improvements in the specific power, power per unit mass, achievable
for concentrated photovoltaics in space.
