Determination of bound-electronic and free-carrier nonlinearities in ZnSe, GaAs, CdTe, and ZnTe

TLDR

The study extends the Z‑scan technique to measure free‑carrier nonlinearities in the presence of bound electronic refraction and two‑photon absorption. Using picosecond Z‑scan measurements at 1.06 µm (and 0.53 µm for ZnSe) on CdTe, GaAs, ZnTe, and ZnSe, the authors extracted σr, β, and n2 from low‑power scans and quantified carrier‑induced fifth‑order refraction from high‑power scans. The measured σr, β, and n2 agree with simple two‑band and band‑filling models, with n2 changing sign near the band edge as predicted by Kramers–Kronig theory. References: Rev.

Abstract

We extend the application of the Z-scan experimental technique to determine free-carrier nonlinearities in the presence of bound electronic refraction and two-photon absorption. We employ this method, using picosecond pulses in CdTe, GaAs, and ZnTe at 1.06 μm and in ZnSe at 1.06 and 0.53 μm, to measure the refractive-index change induced by two-photon-excited free carriers (coefficient σr,), the two-photon absorption coefficient β, and the bound electronic nonlinear refractive index n2. The real and imaginary parts of the third-order susceptibility (i.e., n2 and β, respectively) are determined by Z scans with low inputs, and the refraction from carriers generated by two-photon absorption (an effecitve fifth-order nonlinearity) is determined from Z scans with higher input energies. We compare our experimental results with theoretical models and deduce that the three measured parameters are well predicted by simple two-band models. n2 changes from positive to negative as the photon energy approaches the band edge, in accordance with a recent theory of the dispersion of n2 in solids based on Kramers–Kronig transformations [ Phys. Rev. Lett.65, 96 ( 1990); IEEE J. Quantum Electron.27, 1296 ( 1991)]. We find that the values of σr are in agreement with simple band-filling models.