Phase-sensitive pump-probe measurement of the complex nonlinear susceptibility of silicon across the direct band edge

Published

September 16, 2024

Author(s)

Chad Cruz, John C. Stephenson, Jared Wahlstrand

Abstract

The nonlinear response of materials, an increasingly important aspect of light-matter interaction, can be challenging to measure in highly absorbing materials. Here, we introduce an interferometric technique that enables a direct measurement of the nonlinear complex permittivity in a bulk medium from reflectivity alone. We demonstrate the utility of pump-probe supercontinuum (SC) spectral interferometry in reflection by measuring time-dependent variations in the complex dielectric function (, ) over the visible wavelength range in bulk silicon. Transient phase shifts in the reflected SC due to a near infrared pump pulse allow us to track modifications to , whereas changes in are derived from transient fluctuations in the reflected SC probe amplitude. The ultrafast response is attributed to effective two-photon absorption () and Kerr (2) coefficients. We observe the onset of strong two-photon absorption as the two-photon energy is tuned through the direct band edge of silicon (1 = 3.4 eV). This technique allows straightforward spectroscopic measurements of the (3) nonlinear response at the surface of absorbing materials.

Citation

Optica

Volume

11

Issue

9

Pub Type

Journals

Download Paper

https://doi.org/10.1364/OPTICA.530147

Local Download

Keywords

nonlinear optics, femtosecond, pump-probe, semiconductors

Citation

Cruz, C. , Stephenson, J. and Wahlstrand, J. (2024), Phase-sensitive pump-probe measurement of the complex nonlinear susceptibility of silicon across the direct band edge, Optica, [online], https://doi.org/10.1364/OPTICA.530147, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=957787 (Accessed October 9, 2025)