# Laser-induced incandescence of iron nanoparticles: effects of laser-induced sintering and coalescence

## TL;DR

This paper investigates how laser heating affects iron nanoparticles, explaining unusual behaviors in their incandescence signals.

## Contribution

The study introduces a revised model explaining how coalescence of iron nanoparticles affects laser-induced incandescence signals.

## Key findings

- Laser heating causes iron nanoparticle aggregates to coalesce into spheres before peak incandescence.
- Coalescence reduces absorption cross-section and increases nanoparticle peak temperature.
- The revised model better aligns with measured cooling behavior of coalesced particles.

## Abstract

While time-resolved laser-induced incandescence is a promising technique for characterizing metal nanoparticles in the gas phase, there remain several commonly observed and unexplained features in the data, including larger-than-predicted absorption cross-sections (excessive absorption) and faster-than-predicted cooling rates immediately following peak emission (apparent anomalous cooling). In the case of low melting point metals such as iron, laser-heated aggregates coalesce into spheres (i.e., fully sinter) before the peak of the LII signal is reached. Coalescence may affect the observed TiRe-LII signals in two ways: (i) the transition from aggregates to spheres reduces the absorption cross-section, which affects both the total absorbed laser energy and the intensity of the emitted incandescence in a wavelength-dependent manner; and (ii) surface energy is converted into sensible energy of the nanoparticles, which increases their peak temperature. While the revised LII model does not completely account for the rapid signal decay immediately following the peak signal, the predicted curves align more closely with the measured intensities from coalesced particles during the later cooling times.

The online version contains supplementary material available at 10.1007/s00340-025-08504-0.