Department of Quantum Electronics, Faculty of Physics, Sofia University “St. Kliment Ohridski”, 5 J. Bourchier Blvd., Sofia, BG-1164, BulgariaLaboratory of Optics & Spectroscopy, Georgi Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., BG-1784 Sofia, Bulgaria firstname.lastname@example.org phone +35929795747
Ivan L. Stefanov;Georgi B. Hadjichristov
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 ionmodified 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 v 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 (? = 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.