# Probing the Local Response of Glass-forming Liquids by Laser Excitations

## TL;DR

This study uses laser excitations to investigate the microscopic response and heterogeneity of glass-forming liquids, revealing structure-encoded dynamics and universal scaling behaviors.

## Contribution

It introduces a novel experimental approach to probe the local response of glasses, uncovering non-monotonic length scales and universal excitation scaling relations.

## Key findings

- Heterogeneous response patterns are reproducible in linear excitation regions.
- Non-monotonic dynamical length scales depend on area fraction.
- Universal scaling relation for excitation size and radius of gyration.

## Abstract

The glass is a disordered solid that processes distinct dynamical and elastic properties compared with crystal. How heterogeneous glassy materials can be and to what extent dynamics is encoded with structure and elasticity are long-standing puzzles in glass science. In this experiment, we probed the responses of binary colloidal glasses towards the excitations induced by highly focused laser pulses. We observed very similar excitation patterns when the laser was repeated in the linear region; directly proving that the dynamical heterogeneity is strongly encoded with structure. In the non-linear region, we identified a non-monotonic dynamical length scale as a function of area fraction, resulting from the non-monotonic coupling of momentum transfer in radial and orthogonal directions. Surprisingly, the excitation size and radius of gyration conformed to a universal scaling relation that covered both linear and non-linear regions. Our experiments offered a new strategy of actively probing the response of glassy materials on the microscopic level.