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Stepwise Chirping of Chiral Sculptured Thin Films for Bragg Bandwidth Enhancement

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 Added by Akhlesh Lakhtakia
 Publication date 2020
  fields Physics
and research's language is English




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A stepwise chirping of the periodicity of a chiral sculptured thin film is shown to considerably enhance the bandwidth of the Bragg regime, thereby extending the frequency range of operation as a circular{polarization filter.



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Axially excited chiral sculptured thin films (STFs) are shown to exhibit the circular Bragg phenomenon in the pre-resonant (long-wavelength) regime but not in some parts of the post-resonant (short-wavelength) regime. Chiral STFs act as very good polarization-independent reflectors in the vicinity of material resonances in the latter regime.
The solution of a boundary--value problem formulated for the Kretschmann configuration shows that the phase speed of a surface--plasmon--polariton (SPP) wave guided by the planar interface of a sufficiently thin metal film and a sculptured thin film (STF) depends on the vapor incidence angle used while fabricating the STF by physical vapor deposition. Furthermore, it may be possible to engineer the phase speed by periodically varying the vapor incidence angle. The phase speed of the SPP wave can be set by selecting higher mean value and/or the modulation amplitude of the vapor incidence angle.
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