【International Papers】Anisotropic below bandgap harmonic generation in β-gallium oxide

      Researchers from the Universidade de Lisboa have published a dissertation titled "Anisotropic below bandgap harmonic generation in β-gallium oxide" in Optics Express.

Abstract

      Harmonic generation in wide bandgap semiconductors and dielectrics has attracted a surge of interest as a compact solid-state light source and as a method of mapping the band structure of the material itself. Longer driving wavelengths can support longer electron trajectories and suppress interband transitions, yielding spectra sensitive to crystal orientation and band shapes. Here, we combine a long wavelength laser to drive harmonic generation in a wide band-gap material with applications in photonics and power electronics, beta-gallium oxide (β-Ga₂O₃). We generate harmonics up to the ninth order (H9=3.7 eV) in air, with a ≈ 3.0 μm, 100 kHz, 40 fs mid-infrared (MIR) driving laser in (100) and (010) oriented single crystals of β-Ga₂O₃. We observe odd and even harmonics, spectral interference, and the strong anisotropic response of both odd and even harmonics to the incident laser polarization. Our results are explained in terms of the electronic structure and macroscopic optical properties of β-Ga₂O₃.