Im{χ(3)} spectra of 110-cut GaAs, GaP, and Si near the two-photon absorption band edge

Abstract

Spectra of the degenerate two-photon absorption coefficient com.elsevier.xml.ani.Math@658abd4, anisotropy parameter com.elsevier.xml.ani.Math@be9aea3, and dichroism parameter com.elsevier.xml.ani.Math@56c0b60f of crystalline 110-cut GaAs, GaP, and Si, at 300 K were measured using femtosecond pump-probe modulation spectroscopy over an excitation range in the vicinity of each material’s half-bandgap com.elsevier.xml.ani.Math@5dfbbb38 (overall com.elsevier.xml.ani.Math@1ebebd58 eV or com.elsevier.xml.ani.Math@58e4949a nm). Together, these three parameters completely characterize the three independent components of the imaginary part of the degenerate third-order nonlinear optical susceptibility tensor com.elsevier.xml.ani.Math@b473147. In direct-gap GaAs, these components peak at com.elsevier.xml.ani.Math@be5696c, which is close to the peak at com.elsevier.xml.ani.Math@605a5135 predicted by the Jones-Reiss phenomenological model. The dispersion is comparable with ab initio calculations. In indirect-gap GaP and Si, these components tend to increase with com.elsevier.xml.ani.Math@1ce659e0 over our tuning range. In Si, the dispersion differs significantly from predictions of semi-empirical models, and ab initio calculations do not account for transitions below the two-photon direct bandgap, motivating further investigation. Kleinman symmetry was observed to be broken in all three materials. We also note anomalies observed and their possible origins, emphasizing the advantages of a 2-beam experiment in identifying the contribution of various nonlinear effects.