Polymer banknotes are being increasingly adopted to replace older banknotes. Since banknotes are forensically important substrates for fingermark detection and identification, we present a single-step process to enhance the visualization of fingermarks on banknotes using 40-nm-thick columnar thin films (CTFs) of nickel. This singlestep vacuum technique enhances the quality grade of fingermarks maximally, whether the fingermarks are aged for one or seven days before CTF deposition. This work represents progress over currently available sequences of diverse techniques for enhancing fingermarks on polymer banknotes.
Motivated by the need for reliable optical sensing modalities, we fabricated a doubly chiral sculptured thin film (D-CSTF) of zinc selenide, comprising a structurally left-handed CSTF and a structurally right-handed CSTF deposited consecutively on a glass substrate. Both constituent STFs were sufficiently thick as to exhibit the circular Bragg phenomenon independently and distinctly in the 500–900-nm wavelength range. The fabrication process involved asymmetric serial bideposition through thermal evaporation. All eight circular remittances of the D-CSTF were measured using a variable-angle spectroscopic system. The direction of the incident light was varied so that the azimuthal angle ranged from 0◦ to 70◦ and the polar angle from 0° to 180°. The D-CSTF functions as a bandstop filter for RCP light as well as a bandstop filter for LCP light, regardless of the polar angle and the face that is illuminated, the two stopbands being distinct from each other.
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