In-situ measurements of residual heating during pulse-on-demand femtosecond laser surface microprocessing

Abstract

Femtosecond laser processing offers highly precise structuring with minimal residual heating of materials. However, at high average powers and pulse repetition rates, heating can limit process efficiency. The pulse-on-demand laser operation regime has proven to be an optimal solution for achieving high throughput and quality in laser microstructuring, independent of the scanner’s capabilities. Here, we present in situ measurements of residual heating during femtosecond laser microstructuring. By combining experimental observations with simulations, we investigate residual heat retention in various target materials and its associated effects. A high-speed thermal camera was employed for direct process monitoring, providing spatially and temporally resolved measurements of surface temperatures during laser microstructuring. The results were quantified using finite element–based numerical simulations of the material’s transient thermal response, enabling us to assess the conversion of laser power into unwanted residual heating. Surface topography measurements further contextualize the temperature data within the framework of microprocessing performance. We compare the effects of the pulse-on-demand regime with those observed in quasi-stationary cases, addressing both scanner acceleration compensation and advanced surface shaping achieved through laser repetition rate modulation algorithms. The pulse-on-demand regime’s ability to compensate for irregular scanner movements enables faster and more precise femtosecond laser processing of brittle and heat-sensitive materials.