Replika Mirrors - Nearly Loss-Free Guides For Ultracold Neutrons

The reflectivity of ultracold neutron (UCN) guides produced with a dedicated technique called {\sc Replika} has been studied. The guides are made of nickel, where the surface quality was copied from a glass layer. This results in a surface roughness smaller than 10 \AA. The reflectivity was measured to be 99.9% or higher. Those guides can be used at present or future UCN sources to transport UCN over long distances to the respective experiments without significant losses.