Design of an optical filter as a monochromatic selector from atomic emissions

A bandpass filter with a linearly periodic refractive-index profile is discussed in analogy with the Kronig–Penney model in the band theory of solids. The suggested filter is capable of selecting intense lines from the light emitted by the excitation of neutral and ionized atoms. The particular cases of Ar, Br, and C emissions were considered for the sake of illustration.