Fig. 6
a Normal incidence reflection spectra of the proposed nanohole array-based absorber with the refractive index of hole (n) changing from 1.332 to 1.372. The structural and material parameters are set as h1 = 20 nm, h2 = 250 nm, h3 = 200 nm, ε2 = 3.1, p = 200 nm, and w = 60 nm. b The position of reflection dip and calculated FOM as a function of the refractive index of holes (n = 1.332–1.362)