Abstract: A sample can be illuminated for analysis using apparatus including a light source, a planar waveguide, and a refractive volume. The light source provides light along a propagation vector. The planar waveguide is oriented such that the propagation vector is perpendicular to the normal vector of the planar waveguide and offset from the planar waveguide in a direction parallel to the normal vector of the planar waveguide. The refractive volume is positioned proximate to the planar waveguide and can optically coupling light provided by the light source to the planar waveguide.