Micromachining of Invar Foils with GHz, MHz and kHz Femtosecond Burst Modes.

Simas Butkus,Vytautas Jukna,Domas Paipulas,Valdas Sirutkaitis,Martynas Barkauskas

doi:10.3390/mi11080733

Abstract

In this work, a burst mode laser is used for micromachining of 20 µm–250 µm thick Invar (Fe64/Ni36) foils. Holes were drilled by firing multiple pulses transversely onto the sample without moving the beam (percussion drilling). The utilized laser system generates a burst of a controllable number of pulses (at 1030 nm) with tunable pulse-to-pulse time spacing ranging from 200 ps to 16 ns. The sub-pulses within the burst have equal amplitudes and a constant duration of 300 fs that do not change regardless of the spacing in time between them. In such a way, the laser generates GHz to MHz repetition rate pulse bursts with a burst repetition rate ranging from 100 kHz to a single shot. Drilling of the material is compared with the non-burst mode of kHz repetition rate. In addition, we analyze the drilling speed and the resulting dependence of the quality of the holes on the number of pulses per burst as well as the average laser power to find the optimal micromachining parameters for percussion drilling. We demonstrate that the micromachining throughput can be of an order of magnitude higher when using the burst mode as compared to the best results of the conventional kHz case; however, excess thermal damage was also evident in some cases.

Highlights

Due to the high precision and low thermal damage offered by ultrashort pulse micromachining, femtosecond laser systems are widely applied in both industrial and scientific fields [1]
We have presented results of metal (20–250 μm thick Invar (Fe64/Ni36) foils) percussion drilling experiments carried out with a multi-burst generating femtosecond laser system
Different burst modes were investigated that equate to GHz, MHz and kHz repetition rates

Summary

Introduction

Due to the high precision and low thermal damage offered by ultrashort pulse micromachining, femtosecond laser systems are widely applied in both industrial and scientific fields [1]. A different approach could be used if the high average power laser system operates at high repetitions rates (>10 MHz) In this situation, the fluence may be set near the optimal ablation setting as described in [13]; the pulse-to-pulse time separation becomes small enough for heat accumulation to significantly decrease the end-quality of the micromachined samples [14,15]. The fluence may be set near the optimal ablation setting as described in [13]; the pulse-to-pulse time separation becomes small enough for heat accumulation to significantly decrease the end-quality of the micromachined samples [14,15] It is especially visible at the Gaussian beam periphery and is a typical problem for high average power systems. For the case of the polygon scanners, vector scanning is near impossible, leaving these systems applicable only for specific pattern machining

Methods

Results

Conclusion