A beamline mirror or supermirror. mirror with a single material as a reflecting surface mirror with stacked, multiple layers as a reflecting surface description of this mirror Reflectivity as function of wavelength external material outside substrate The m value for a supermirror, which defines the supermirror regime in multiples of the critical angle of Nickel. An array describing the thickness of each layer A NXshape group describing the shape of the mirror Numerical description of the surface figure of the mirror.