Is the ultra-fast transformation of bismuth non-thermal?

TL;DR

This paper investigates whether the ultrafast transformations in femtosecond laser-excited bismuth are non-thermal or thermal, concluding that all observed changes are purely thermal based on optical property analysis.

Contribution

It provides a definitive analysis demonstrating the thermal nature of ultrafast bismuth transformations, clarifying previous experimental controversies.

Findings

All femtosecond laser-induced transformations in bismuth are thermal.

Optical properties analysis shows no evidence of non-thermal melting.

The study resolves conflicting interpretations from previous experiments.

Abstract

Transient state of femtosecond laser excited bismuth has been studied by various groups with time-resolved optical, x-ray, and electron probes at the deposited energy density from below through up to several times the equilibrium enthalpy of melting. However, the interpretations of the experimental results are controversial: the optical probes reveal the absence of transition to the melting phase while the authors of x-ray and electron diffraction experiments claim the observation of ultrafast non-thermal melting. The presented analysis, based on temperature dependence of bismuth optical properties, unequivocally shows a purely thermal nature of all the observed fs-laser induced transformations in bismuth.