Abstract
Binary surface reliefs with sub-wavelength features making up a pseudorandom pattern based on mathematical Galois fields GF(pm) [1, 2] can scatter incoming waves into a large number of diffraction maxima within a huge solid angle. A one-dimensional (1D) Galois number sequence can be folded into a two-dimensional (2D) array by the sino-representation [2]. This concept was been verified for acoustic waves a long time ago [3, 4] and is investigated here for visible light and THz waves. Our Galois diffusers are designed as reflection reliefs and realised by electron beam lithography for the optical regime and UV photolithography for the THz regime. Our results show that optical and THz Galois surfaces are excellent diffusers for electromagnetic waves; they distribute the reflected intensity evenly over a large number of maxima nearly within the entire half solid angle in the backward direction.
Highlights
For the realisation of optical diffusers by structuring the surface two different approaches are possible: the surfaces can be roughened or diffractive optical elements (DOEs) can be created on the surfaces
In order to show that DOEs with features on a sub-wavelength scale can scatter incoming waves over a large number of maxima within a huge scattering angle (≈ 180◦), we have chosen an approach well known from acoustics, so called Galois diffusers
They represent a special kind of Dammann gratings [11, 12], designed as binary reflection gratings, where the surface reliefs represent pseudorandom sequences based on mathematical Galois fields GF(pm) [1, 2]
Summary
Binary surface reliefs with sub-wavelength features making up a pseudorandom pattern based on mathematical Galois fields GF(pm) [1, 2] can scatter incoming waves into a large number of diffraction maxima within a huge solid angle. A one-dimensional (1D) Galois number sequence can be folded into a two-dimensional (2D) array by the sino-representation [2]. This concept was been verified for acoustic waves a long time ago [3, 4] and is investigated here for visible light and THz waves. Our results show that optical and THz Galois surfaces are excellent diffusers for electromagnetic waves; they distribute the reflected intensity evenly over a large number of maxima nearly within the entire half solid angle in the backward direction.
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