Optical chirality in AgCl-Ag thin films through formation of laser-induced planar crossed-chain nanostructures

Abstract

Irradiation of AgCl-Ag thin films by a linearly polarized He-Ne laser beam results in the formation of self-organized periodic nanostructures. As a result of secondary irradiation of the initially exposed sample by the same linearly polarized He-Ne laser beam, but with different orientations of polarization, a complex crossed-chain nanostructure forms. We found that such a complex nanostructure has noticeable chirality and increased optical anisotropy, resulting in optical activity of the sample. Double exposure produces two gratings, crossing each other with angle α, which leads to the formation of crossed building blocks with chiroptical effects. It is established that the amount and the sign of the angle between the two laser-induced gratings (±α) determine the amount and the direction of rotation of the linearly polarized probe beam, respectively. We have also observed an induced anisotropy-dependent ellipticity for the probe light, which is passed through the sample. It is shown that the amount of ellipticity depends on the angle α.

Enhanced Photo-Induced Optical Activity of Crisscrossed Self-Organized Gratings in Photosensitive Nanolayers by Introducing Bi-Periodicity

“…Our studies [10] show that the crisscrossed mono-periodic SPNs exhibit the highest optical activity compared to other mentioned methods. The common factor between the last two methods (cases (ii) and (iii)) is the bi-periodicity of the produced SPNs.…”

“…Consequently, a periodic structure made of Ag-NPs is generated according to the interference pattern. Since the shape of an interference pattern depends on the wavelength and polarization states of the interfering lights, the formed SPNs inherently encode this information [9,10,16,21,25]. Without the AgCl layer, the TE n -mode cannot be excited, resulting in no interference and no formation of spontaneous periodic nanostructures.…”

“…The optical active medium rotates the plane of polarization of a passing-through probe beam due to two structural and geometrical properties: (i) anisotropy of the photonic material and (ii) optical chirality of elements formed within the medium. Increasing the anisotropy of the medium enhances optical chirality [8][9][10].…”

“…In all the aforementioned cases, the information related to the sign and polarization state of the incident light is recorded by the formed SPN [9][10][11]. Specifically:…”

“…ii. Formation of two identical crisscrossed linear SPNs (referred to as mono-periodic SPNs) with different angles between them (angle α) [10].…”