Surface temperature during ultrashort pulsed laser micromachining measured for the first time: a new paper of our researchers

13.01.2021
                                                           

An article of our researchers J. Martan, L. Prokešová, D. Moskal, B. C. Ferreira de Faria, M. Honner and V. Lang “Heat accumulation temperature measurement in ultrashort pulsed laser micromachining” has been published in the journal International Journal of Heat and Mass Transfer.

The article presents first time ever measurement of surface temperature during ultrashort pulsed laser micromachining and describes the developed measurement system and calibration of infrared radiometry.

Abstract

Ultrashort pulse laser micromachining is affected by the heat accumulation resulting from the residual heat from previous laser pulses on the sample surface. Up to now, most of the works analysed the accumulation by numerical modelling. The present work focused on development and application for the first time of a measurement system of heat accumulation temperature directly during the processes in nanosecond and microsecond time ranges. The measurement system was based on the infrared radiometry and contained liquid nitrogen cooled fast HgCdTe photodetector and paraboloid mirrors. Micromachining of grooves was done using a 14 W picosecond laser with different pulse energies, repetition frequencies and scanning speeds. Calibration of the measurement system was done in order to obtain temperatures from the measured signal. The calibration was not straightforward due to very small laser spot (25 μm), small signal and changing of the size of the heated area for low scanning speeds. Obtained heat accumulation temperature ranged from 300°C to 2600°C for scanning speeds from 8 m/s to 0.07 m/s and pulse energies from 0.1 µJ to 100 µJ. According to the scanning electron microscope (SEM) images, the material was already partially melted (small droplets on boarders) for low scanning speeds. Surface roughness and ablation rate were determined by 3D confocal laser microscope. Good correlation was found between the roughness and the heat accumulation temperature, thus confirming the validity of calibration. Measured heat accumulation temperature was surprisingly the highest for the most efficient ablation parameters and at the same time low surface roughness was achieved.

You can download the paper for free (for 50 days) at this link.