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

Abstract

High power ultrafast lasers are nowadays able to provide high ablation rates and meet the technical requirements and performances needed for many industrial applications. However depositing more energy into the target may induce heat accumulation, and consequently enhances the ablation efficiency as well as introduces some detrimental effect on the processing quality. So, the key issue is to improve throughput while maintaining the processing quality and preventing from any deformation of the work piece. In this paper we present some comparative results on surface ablation of Aluminum, Copper, Molybdenum and stainless steel in both picosecond and femtosecond regimes. Trials have been performed using two high power Yb-doped fibre ultrafast lasers which are tunable in pulse duration (350 fs to 10 ps, up to 20 W). Samples have been characterized with confocal microscopy and scanning electron microscopy. We discuss the effect of pulse duration, repetition rate, fluence and energy dose per mm on ablation efficiency, processing quality and ripples formation.

[INVITED] Ultrafast laser micro-processing of transparent material

“…Fig. 8 shows their result of the measured temperature distribution [72]. Within the range of 73 mm from the focus of the processing pulse, they described that it was difficult to measure temperature due to the onset of large background signals, as shown in the inset of Fig.…”

“…On the other hand, high-repetition ultrafast laser pulses can induce smooth modifications at a high speed [8][9][10]. Hashimoto et al measured the temperature dynamics inside glass by time-resolved micro-Raman spectroscopy during high-repetition-rate ultrafast laser microprocessing [72]. It has been shown that temperature dynamics is quite important because the processed area is strongly influenced by the heat accumulation effect.…”

“…7 [72]. They used an amplified Ytterbium fiber laser system producing 600-fs pulses at a wavelength of 1044 nm and a repetition rate of 1 MHz.…”

Ultrashort pulse laser processing of silica at high repetition rates—from network change to residual strain

“…The resulting modifications range from isotropic refractive index changes, 3 artificial birefringence due to so-called nanogratings 4,5 to microscopic voids due to a confined microexplosion. 7,8 After rapid cooling (typical cooling rates >10 6 K/s), the molten glass resolidifies, allowing for the local bonding of glass interfaces with high stability. 7,8 After rapid cooling (typical cooling rates >10 6 K/s), the molten glass resolidifies, allowing for the local bonding of glass interfaces with high stability.…”

“…6 Moreover, when using high repetition rates, the laser pulses act as a local heat source, leading to temperatures well above the melting temperature of the glass. 7,8 After rapid cooling (typical cooling rates >10 6 K/s), the molten glass resolidifies, allowing for the local bonding of glass interfaces with high stability. 9 Based on the confined transfer of heat, even different glass combinations can be successfully bonded together.…”