Extracting Quantitative Dielectric Properties from Pump-Probe Spectroscopy

TL;DR

This paper introduces a model-independent method to extract quantitative transient dielectric properties from pump-probe spectroscopy data, enabling unambiguous analysis of photoexcited states in various materials.

Contribution

The authors develop and validate a novel approach to convert differential spectra into dielectric functions, improving quantitative interpretation of pump-probe measurements.

Findings

Method accurately retrieves dielectric changes in semiconductors.

Benchmarking shows consistency with frequency domain interferometry.

Applicable to diverse materials and existing datasets.

Abstract

Optical pump-probe spectroscopy is a powerful tool for the study of non-equilibrium electronic dynamics and finds wide applications across a range of fields, from physics and chemistry to material science and biology. However, a shortcoming of conventional pump-probe spectroscopy is that photoinduced changes in transmission, reflection and scattering can simultaneously contribute to the measured differential spectra, leading to ambiguities in assigning the origin of spectral signatures and ruling out quantitative interpretation of the spectra. Ideally, these methods would measure the underlying dielectric function (or the complex refractive index) which would then directly provide quantitative information on the transient excited state dynamics free of these ambiguities. Here we present and test a model independent route to transform differential transmission or reflection spectra, measured via conventional optical pump-probe spectroscopy, to changes in the quantitative transient dielectric function. We benchmark this method against changes in the real refractive index measured using time-resolved Frequency Domain Interferometry in prototypical inorganic and organic semiconductor films. Our methodology can be applied to existing and future pump-probe data sets, allowing for an unambiguous and quantitative characterisation of the transient photoexcited spectra of materials. This in turn will accelerate the adoption of pump-probe spectroscopy as a facile and robust materials characterisation and screening tool.