Linear Dichroism in ZnO/Ag Nanocomposite Films under Femtosecond Laser Radiation: Implications for Polarization Rotators

In this paper, we investigate linear dichroism in nanocomposite ZnO/Ag thin films caused by femtosecond laser irradiation. It was found that laser radiation with a wavelength near plasmon resonance of silver nanoparticles (515 nm), pulse duration 224 fs, pulse repetition rate 200 kHz and an average energy density ranging from 30 mJ/cm 2 to 131 mJ/cm 2 causes the formation of linear dichroism with maximum at 56 mJ/cm 2 . The detected optical anisotropy was associated with the anisotropy of the nanoparticle shape, and their reorientation parallel to laser polarization, which was studied via electron microscopy. The laser-modified film demonstrated optical rotation in the visible wavelength range. The highest efficiency when using radiation with linear polarization and a wavelength of 637 nm is obtained if the angle between the analyzer and the nanoparticles was 45°. These results can be used in the future to manufacture polarization rotators operating in the field of optical data storage.