Laser assisted modification of poled silver-doped nanocomposite soda-lime glass

Abstract

Thermal poling assisted homogenization of polydisperse Ag nanoparticles embedded in the soda-lime glass is demonstrated. The homogenization leads to the narrowing of the localized surface plasmon resonance. The subsequent irradiation with linearly polarized ultrashort laser pulses induces spectrally defined and four times larger dichroism than in non-poled sample.Metal-doped nanocomposite glasses are of interest for their unique linear and nonlinear optical properties. Simple and low cost fabrication technique of nanocomposite glass is based on ion exchange. In this technique the metal ions are embedded in glass matrix by ion exchange with further annealing in a reducing atmosphere, resulting in randomly distributed metal aggregates with an exponentially decreasing filling factor across the depth [1]. The optical properties of nanoparticles can then be controlled by ultrashort laser pulses with a wavelength close to localized surface plasmon resonance [2]. However, a non-uniform distribution of nanoparticles in the glass matrix complicates any laser assisted modification. In this work we demonstrate the poling assisted homogenization of Ag nanoparticles embedded in soda-lime glass matrix, which improves laser assisted modification of optical properties.The polydisperse nanocomposite sample prepared from soda-lime float glass by Ag + -Na + ion exchange method was provided by CODIXX AG. The spherical Ag nanoparticles of 30-40 nm mean diameter were distributed in a thin surface layer of several micrometers thickness with the high filling factor close to the surface. The sample was thermally poled in air inside the oven using pressed-contact electrodes, with the anode facing the Ag-doped area. The laser modification of Ag nanoparticles was performed using a regeneratively amplified, mode-locked Yb:KGW based ultrafast laser system (Pharos, Light Conversion Ltd.). The laser system was operating at 515 nm (frequency doubled) and 200 kHz repetition rate. The laser beam was focused on the top of sample via a ×5 (NA=0.13) objective lens. The modification of poled area was carried out using 1 ps pulse duration, linear polarization, 0.5 mm/s writing speed with 5 µm interline distance, 10000 pulses/mm density and the varying laser pulse intensity from 2.2×10 10 W/cm 2 to 4.4×10 11 W/cm 2 , i.e. below the damage threshold of soda-lime glass. For the modification of pristine area we used 700 fs pulses, linear polarization, 5 mm/s speed with 5 µm interline distance, 40000 pulses/mm density and the intensities from 5.0×10 10 W/cm 2 to 2.3×10 11 W/cm 2 . For the optical characterization, the absorption spectra of pristine and poled areas were taken with UV-VIS-NIR spectrophotometer (Varian, CARY 500) and optical characterization of modified micro-areas was made with UV-VIS-NIR imaging spectrometer (Andor, Shamrock SR-303i) and VIS microspectrometer system (Olympus BX51, CRAIC). The spectral dependence of modified Ag-doped glass for s-and p-polarizations was measured by inserting linear polarizer before the sample. Image...