Paper Authors and Title
Iain Darroch (Technological University Dublin), Michael Murray, Suzanne Martin, Sabade Gul, Steven Bryant, Milana Trifkovic, Izabela Naydenova, “Effect of graphene quantum dots on the optical properties of photopolymer layers”
Abstract
Photopolymer nanocomposites are a class of optical materials that utilise nanoparticles of varying sizes and refractive index to achieve control over the mechanical, optical and thermal properties of the photonic devices recorded in them.
Research was carried out to determine the optical effects of graphene quantum dots (GQD’s) on photopolymer layers, and their suitability for holographic recording. GQD’s are graphene particles of 10-20 nm measured by Dynamic light scattering. The dispersion method of the GQDs in the layers was optimised to achieve doping levels as high as 5% wt/wt. Drop-casting was used to produce high optical quality layers needed for holographic recording.
The refractive index of the nanocomposite samples was measured using a refractometer at 532 nm and 632 nm. With peak refractive indexes of 1.552 ± 0.019 and 1.549 ± 0.027 measured respectively. These measured indexes are from the peak indices from samples at 60 hours & 6 hours.
Drop cast samples were used to record holographic gratings using a 532 nm laser source, at intensities of 5 mW/cm2, 10 mW/cm2, and 15 mW/cm2. The diffraction efficiency of the gratings and their respective Bragg angular selectivity curves were measured to determine the optimum level of GQD doping. It was found that the highest values for refractive index (1.552), grating efficiency (80%), and refractive index modulation (2.6×10-3) were found at 0.25% wt/wt GQD concentration in the photosensitive layer. This level of high modulation demonstrates the viability of GQD’s as a dopant for altering the optical properties of photopolymer layers.