Picosecond measurement of absorptive and refractive optical nonlinearities in GaP at 532 nm

Abstract

Picosecond time-resolved pump-probe and Z-scan measurements are used to investigate the nonlinear refraction and absorption associated with intense picosecond excitation above the indirect band edge of GaP. The pump-probe results reveal both an instantaneous absorption feature, which is consistent with two-photon absorption, and a long-lived feature that is associated with the generation of free carriers by linear indirect absorption. Z scans conducted with pulses of 25- and 95-ps duration indicate that, for these pulse widths, the nonlinear refraction in GaP is dominated by the linear generation of free carriers and that the role of the electronic Kerr effect is negligible. The measured free-carrier refraction is compared with the value predicted from a simple model based on band filling. This model predicts that the primary contribution to the index change at the applied optical frequency arises from holes blocking direct transitions near the zone center and that similar blocking of indirect transitions has a negligible effect on the index.

Three-photon absorption and Kerr nonlinearity in undoped bulk GaP excited by a femtosecond laser at 1040 nm

“…For all the applications, it is important to know the optical nonlinearity of GaP under the relevant pump lasers. Some nonlinear characteristics of GaP have previously been studied by using picosecond or nanosecond lasers [8,9]. However, quoted experimental data discrepancies as large as two orders of magnitude can be found [8], because of the lack of stable pulse duration and good laser beam of pump sources used in the experiments as well as because of differing theoretical models used to process the experimental data.…”

Ultrafast Dephasing of Light in Strongly Scattering GaP Nanowires

“…A minimum absorption length α −1 of 49.9 ± 4 µm is found, corresponding to a change of the imaginary refractive index ∆κ = c 0 α/4πν of (1.0 ± 0.2) × 10 −3 . Using a free-carrier absorption cross section of GaP of 1.1 × 10 −18 cm −2 [22], our value for ∆κ amounts to a free-carrier density of 2 × 10 20 cm −3 , which is a realistic density for the strong optical pumping regime under study.…”