Fig. 7
a Focal spots from microlenses are independent of the out-of-roundness error σ of nanoholes. The focusing properties do not show a clear change when σ = 0 (rounded nanoholes) in Fig. 5 is increased to a1 σ = 0.4, a2 σ = 0.7 with a horizontal distorted direction, and a3 σ = 0.7 with a perpendicular distorted direction. b Introduction of spatial randomness into the positions of nanoholes. Deviation directions are randomly different from hole to hole, but the deviation length δ is kept constant for each hole. The same focusing patterns are obtained when the deviation length b1 δ = 0, b2 δ = 50 nm, and b3 δ = 100 nm