Time-resolved thermal lens spectroscopy of glassy dynamics in supercooled liquids: theory and experiments

TL;DR

This paper introduces a novel ultrafast thermal lens spectroscopy method to investigate glassy dynamics by simultaneously measuring specific heat and thermal expansivity, providing insights into relaxation processes in supercooled liquids.

Contribution

It develops a detailed theoretical model and experimental approach for time-resolved thermal lens spectroscopy to study glass transition dynamics.

Findings

Determined relaxation strength and frequency across a wide temperature range.

Successfully analyzed thermoelastic transients in supercooled liquids.

Extended spectroscopy bandwidth for thermal dynamic measurements.

Abstract

Specific heat and linear thermal expansivity are fundamental thermal dynamics and have been proven as interesting relaxing quantities to investigate in glass transition and glassy state. However, their possibility has much less been exploited compared to mechanical and dielectric susceptibilities due to the limited spectroscopy bandwidth. This work reports on simultaneous spectroscopy of the two by making use of ultrafast time-resolved thermal lens (TL) spectroscopy. Detailed modeling of the thermoelastic transients of a relaxing system subjected to ultrashort laser heating is presented to describe the TL response. The model has been applied to analyze a set of experimentally recorded TL waveforms, allowing the determination of relaxation strength and relaxation frequency from sub-kilohertz to sub-100 MHz and in a wide temperature range from 200-280 K.