# Time-domain Brillouin scattering for the determination of laser-induced temperature gradients in liquids

## TL;DR

This paper introduces a novel ultrafast optical method using time-domain Brillouin scattering to accurately measure local temperature gradients in liquids caused by laser heating, with applications in complex multilayer systems.

## Contribution

The paper presents a new ultrafast pump-probe technique that uses TDBS to determine local temperature distributions in liquids and multilayer systems, enhancing temperature measurement precision.

## Key findings

- Successfully measured temperature gradients in glycerol at different laser powers.
- Demonstrated sensitivity of TDBS to local temperature variations.
- Applied TDBS to complex multilayer systems for thermal diffusion analysis.

## Abstract

We present an optical technique based on ultrafast photoacoustics to precisely determine the local temperature distribution profile in liquid samples in contact with a laser heated optical transducer. This ultrafast pump-probe experiment uses time-domain Brillouin scattering (TDBS) to locally determine the light scattering frequency shift. As the temperature influences the Brillouin scattering frequency, the TDBS signal probes the local laser-induced temperature distribution in the liquid. We demonstrate the relevance and the sensitivity of this technique for the measurement of the absolute laser-induced temperature gradient of a glass forming liquid prototype, glycerol, at different laser pump powers - i.e. different steady state background temperatures. Complementarily, our experiments illustrate how this TDBS technique can be applied to measure thermal diffusion in complex multilayer systems in contact to a surrounding liquid.