Time-resolved Micro-Raman Measurement of Temperature Dynamics during High-Repetition-Rate Ultrafast Laser Microprocessing

We employed time-resolved micro-Raman spectroscopy to investigate the temperature dynamics inside glass during high-repetition-rate femtosecond laser microprocessing. We measured the temperature evolutions as functions of the distance from the focus of femtosecond laser pulses, although it was difficult to acquire Raman spectra at locations near the focus due to the onset of strong background emissions. The measured temperature data were fitted by, taking the heat accumulation of successive laser pulses into account. We further investigated the dependence of temperature increase on the processing parameters. Our results suggest that the monitoring of thermal process is useful not only for process optimization but also for detailed in situ analysis of thermal process in highrepetition-rate femtosecond laser microprocessing.