Characteristics of Multi-photon Absorption in a β-Ga2O3 Single Crystal

We have investigated the characteristics of multi-photon absorption (MPA) in a β-Ga2O3 single crystal at room temperature using the photoluminescence (PL) of the self-trapped exciton (STE) as a probe. From analysis of the excitation fluence dependence of the integrated STE-PL intensities at various excitation photon energies, we clearly confirmed the occurrence of two-, three-, four-, and five-photon absorption processes. The optical transition energies in the four- and five-photon absorption processes are almost consistent with the transition energies between lower-lying valence bands and the conduction-band bottom at the Γ point and those at critical points away from the Γ point, which are taken from previously reported first-principles calculations, respectively.