Laser characterization of the depth profile of complex refractive index of PMMA implanted with 50 keV silicon ions

The depth profile of the complex refractive index of silicon ion (Si⁺) implanted polymethylmethacrylate (PMMA) is studied, in particular PMMA implanted with Si⁺ ions accelerated to a relatively low energy of 50 keV and at a fluence of 3.2 × 10¹⁵ cm^-2. The ion-modified material with nano-clustered structure formed in the near(sub)surface layer of a thickness of about 100 nm is optically characterized by simulation based on reflection ellipsometry measurements at a wavelength of 632.8 nm (He-Ne laser). Being of importance for applications of ion-implanted PMMA in integrated optics, optoelectronics and optical communications, the effect of the index depth profile of Si⁺-implanted PMMA on the profile of the reflected laser beam due to laser-induced thermo-lensing in reflection is also analyzed upon illumination with a low power cw laser (wavelength 532 nm, optical power 10 – 50 mW).