Laser beam reflection by nano-designed two-layer nanostructured carbonic material formed in transparent hydrocarbon polymer by ion implantation

We investigated laser beam reflection by optically-transparent hydrocarbon polymeric material subjected to low-energy ion implantation. In our study were measured 5 mm-thick plates of polymethylmethacrylate (PMMA) implanted with silicon ions (Si⁺) accelerated to a relatively low energy of 50 keV at Si⁺ fluence of 10¹⁶ ions/cm². Due to ion-produced destruction of the polymer network and reorganization of the organic structure in a depth of PMMA plate, a buried ion-modified layer with ~ 80 nm thickness is formed within the PMMA. The material in this ultra-thin nano-sized layer beneath the top surface of PMMA (in a depth of ~ 100 nm) is organized in carbon nanoclusters with a mean size of about 2 - 3 nm. The nonlinear gradual in-depth distribution of the complex refractive index in the nanostructured region of the polymer results in a significant modification of the reflection of coherent light by the formed structure. Also, the reflected beam undergoes a strong laser-induced photothermal interface lensing upon irradiation by CW laser ( λ= 532 nm) with an optical power above 30 mW. The presence of thermo-lenses can limit the optical and photonic applications of transparent ion-implanted polymers. Here, this negative effect is studied as dependent on both incident laser power and incidence angle of the laser beam.