Photo-induced change of refractive index and transparency in Bi2Te3 films

TL;DR

This study demonstrates that femtosecond laser irradiation can significantly modulate the refractive index and transparency of Bi2Te3 thin films, enabling potential applications in optical device fabrication.

Contribution

It reveals a novel laser-induced photooxidation process that alters the optical properties of Bi2Te3 films, which was not previously documented.

Findings

Refractive index increased to 5.9 in near-infrared.

Refractive index decreased by a factor of ~3 after laser exposure.

Transmittance increased to ~96% in near-infrared.

Abstract

We report on an 800 nm femtosecond laser beam induced giant refractive index modulation and enhancement of near-infrared transparency in topological insulator material Bi2Te3 thin films. An ultrahigh refractive index of up to 5.9 was observed in the Bi2Te3 thin film in near-infrared frequency. The refractive index dramatically decreases by a factor of ~ 3 by an exposure to the 800 nm femtosecond laser beam. Simultaneously, the transmittance of the Bi2Te3 thin films markedly increases to ~ 96% in the near-infrared frequency. The Raman spectra provides strong evidences that the observed both refractive index modulation and transparency enhancement result from laser beam induced photooxidation effects in the Bi2Te3 thin films. The Bi2Te3 compound transfers into Bi2O3 and TeO2 under the laser beam illumination. These experimental results pave the way towards the design of various optical devices, such as near-infrared flat lenses, waveguide and holograms, based on topological insulator materials.