Precision and resolution in laser direct microstructuring with bursts of picosecond pulses

Abstract

Pulsed laser sources facilitate various applications, including efficient material removal in different scientific and industrial applications. Commercially available laser systems in the field typically use a focused laser beam of 10-20 μm in diameter. In line with the ongoing trends of miniaturization, we have developed a picosecond fiber laser-based system combining fast beam deflection and tight focusing for material processing and optical applications. We have predicted and verified the system's precision, resolution, and minimum achievable feature size for material processing applications. The analysis of the laser's performance requirements for the specific applications of high-precision laser processing is an important aspect for further development of the technique. We have predicted and experimentally verified that maximal edge roughness of single-micrometer-sized features was below 200 nm, including the laser's energy and positioning stability, beam deflection, the effect of spot spacing, and efficient isolation of mechanical vibrations. We have demonstrated that a novel fiber laser operating regime in bursts of pulses increases the laser energy stability. The results of our research improve the potential of fiber laser sources for material processing applications and facilitate their use through enabling the operation at lower pulse energies in bursts as opposed to single pulse regimes.

Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses

“…For longer time spans and a higher number of pulses, heat accumulation highly dominates laser processing, leading to higher energy specific volumes as well as significantly higher roughness, which is also the case for longer pulses in the ns and μs regime due to the emerging occurrence of melting. Beside materials processing with ultra-short burst pulses with intra-burst repetition rates in the MHz and GHz range, processing with THz intra-burst repetition rates (corresponding to delay times between subsequent pulses of several ps) is also a subject of investigation [20,[148][149][150][151][152]. However, in this regime, matter reacts to excitation with subsequent pulses similar like to excitation with longer pulses in the same time domain.…”

Using harmonic beam combining to generate pulse-burst in nonlinear optical laser

“…The great precision reached by ultrashort lasers working in ultrashort pulse-burst [1] provides new machining regimes of structuring rate and surface quality. [2] Research on the removal rate and surface roughness affected by the number of pulses in a burst [3] reveals the optimum point of two [4] or several [5] pulses for different materials. [6] With pulses added into the burst, lasers perform better than a single pulse with the same average power, [4,5] but the performance of pulse-burst mode drops when the burst contains too many pulses.…”

“…[8] The thin layer on the surface absorbs the energy of the laser and ablates into plasma with a shock wave last nanosecond, in the next step, the plasma with particle around the processing area shield the following laser pulses and decrease the ablation rate. [6,7] Since pulse-burst is generated by pulse-picker such as electro-optic devices, the amplitude of pulses in the burst is not constant, especially when the last pulse is more intense, [1,3,5] and the repetition rate of pulses is fixed and determined by the oscillator. To push further the application of burst mode lasers, a new approach is needed for meeting more processing requirements of pulses in amplitude and repetition rate adjustable.…”

Picosecond laser microvia drilling of ABF material using MHz burst mode

“…Consequently, the arising laser pulse energies of up to some 100 μJ lead to a laser fluence that is significantly above the well-known optimum for maximizing the ablation efficiency and rate [24]. For scaling the laser pulse energies closer to the optimum ablation efficiency, so-called laser burst mode can be used to split a laser pulse into at least two and typically up to a few hundred intra-burst pulses with a temporal intra-burst interval in the nanosecond regime [24][25][26][27][28][29][30][31].…”