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

• Published in: Journal of applied physics 2021-05, Vol.129 (18)
• Main Authors: Furey, Brandon J., Barba-Barba, Rodrigo M., Carriles, Ramon, Bernal, Alan, Mendoza, Bernardo S., Downer, Michael C.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Absorptivity; Anisotropy; Anomalies; Applied physics; Dichroism; Dispersion; Energy gap; Excitation spectra; Gallium phosphides; Mathematical models; Parameters; Photon absorption; Photons; Spectrum analysis; Tensors
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0047478

Spectra of the degenerate two-photon absorption coefficient β ( ω ), anisotropy parameter σ ( ω ), and dichroism parameter δ ( ω ) = [ σ ( ω ) + 2 η ( ω ) ] / 2 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 E g / 2 (overall 0.62 < ℏ ω < 1.91 eV or 2000 > λ > 650 nm). Together, these three parameters completely characterize the three independent components of the imaginary part of the degenerate third-order nonlinear optical susceptibility tensor Im { χ a b c d ( 3 ) ( ω ) }. In direct-gap GaAs, these components peak at ℏ ω ≈ 0.78 E g, which is close to the peak at ℏ ω = 0.71 E g 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 ℏ ω 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.