Terahertz emission from indium oxide films on MgO substrates excited at a photon energy below the bandgap

摘要

Indium oxide (In2O3) films grown on MgO substrates by thermal oxidation were excited by femtosecond laser pulses having photon energy lower than the bandgap. The emission of terahertz (THz) pulse was observed using time domain spectroscopy in the reflection-geometry excitation. Results show that THz generation saturates at an excitation fluence of ~400 nJ/cm2. Although two-photon absorption has been ruled out, the actual THz emission mechanism and still has to be verified and is temporarily attributed to carriers from defect level absorption possibly being driven by a strain field due to the lattice mismatch between the In2O3 and the MgO substrate.