Exploring extreme thermodynamics in nanoliter volumes through stimulated Brillouin-Mandelstam scattering

TL;DR

This study demonstrates the use of stimulated Brillouin-Mandelstam scattering in nanoliter liquid volumes within sealed optical fibers to explore extreme thermodynamic states, enabling precise control and measurement of material properties under high pressure and temperature variations.

Contribution

The paper introduces a novel experimental approach for probing liquids under extreme thermodynamic conditions using a sealed fiber system with high optoacoustic confinement and Brillouin gain.

Findings

Achieved spatially resolved Brillouin measurements in nanoliter liquid volumes.

Controlled temperature and pressure independently over wide ranges.

Observed significant tunability of Brillouin frequency shift (>40%) in tiny liquid samples.

Abstract

Examining the physical properties of materials - particularly of toxic liquids - under a wide range of thermodynamic states is a challenging problem due to the extreme conditions the material has to be exposed to. Such temperature and pressure regimes, which result in a change of refractive index and sound velocity can be accessed by optoacoustic interactions such as Brillouin-Mandelstam scattering. Here we experimentally demonstrate Brillouin-Mandelstam measurements of nanoliter volumes of liquids in extreme thermodynamic regimes. We use a fully-sealed liquid-core optical fiber containing carbon disulfide; within this waveguide, which exhibits tight optoacoustic confinement and a high Brillouin gain of (32.2 $\pm$ 0.8) 1/(Wm), we are able to conduct spatially resolved measurements of the Brillouin frequency shift. Knowledge of the local Brillouin response enables us to control the temperature and pressure independently over a wide range. We observe and measure the material properties of the liquid core at very large positive pressures (above 1000 bar), substantial negative pressures (below -300 bar) and we explore the isobaric and isochoric regimes. The extensive thermodynamic control allows the tunability of the Brillouin frequency shift of more than 40% using only minute volumes of liquid. This work opens the way for future studies of liquids under a variety of conventionally hard-to-reach conditions.