Tunable Polarization and Surface Relief Holographic Gratings in Azopolymer Nanocomposites with Incorporated Goethite (α-FeOOH) Nanorods

Lian Nedelchev,Velichka Strijkova,David S. Schmool,Elena Stoykova,Nataliya Berberova-Buhova,Georgi Mateev,Dimana Nazarova,Verónica Salgueiriño

doi:10.3390/photonics8080306

Abstract

We employ two approaches to tune the properties of concurrently inscribed volume polarization and surface relief gratings in nanocomposite thin films containing the azopolymer PAZO (poly[1-4-(3-carboxy-4-hydrophenylazo)benzensulfonamido]-1,2-ethanediyl, sodium salt]) and goethite (α-FeOOH) nanorods. The first one is applied on the stage of sample preparation by varying the concentration of the goethite nanorods from 0% to 15%. Then, different angles between the recording beams are set in the holographic scheme, which allow us to obtain gratings with spatial periods in the range from 0.86 to 2.51 µm. Surface relief modulation close to 300 nm is achieved as well as total diffraction efficiency in the ±1 diffracted orders of more than 50%. The influence of the incorporated goethite nanorods on the properties of both volume birefringence and the surface relief grating are discussed.

Highlights

Accepted: 28 July 2021Holography offers an unparalleled flexibility in forming diffractive optical elements (DOE) with tunable or customizable characteristics [1,2,3]
Polarization, or vectorial holography enables the creation of advanced diffractive elements, referred to as 4G optics, in which the media birefringence is spatially modulated across the surface of the optical element [14,15]
In order to further analyze the optical properties of this nanocomposite, in this work we study the characteristics of polarization holographic gratings in thin film samples containing the azopolymer PAZO and goethite nanorods

Summary

Introduction

Accepted: 28 July 2021Holography offers an unparalleled flexibility in forming diffractive optical elements (DOE) with tunable or customizable characteristics [1,2,3]. By exposing photosensitive material to an interference pattern in a holographic setup with varying recording angles, gratings with spatial periods from hundreds of nanometers up to tens of microns can be produced, reaching diffraction efficiencies as high as 90% [2]. Polarization, or vectorial holography enables the creation of advanced diffractive elements, referred to as 4G optics, in which the media birefringence is spatially modulated across the surface of the optical element [14,15]. Polarization holography requires media with specific optical properties such as high photoinduced anisotropy, birefringence ∆n, or dichroism ∆D. Guest-host systems were used, where azo dye was dispersed in a polymer matrix [16]. They have certain shortcomings, including lower stability

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