Proceedings Article | 23 February 2010
KEYWORDS: Laser ablation, Micromachining, Picosecond phenomena, Pulsed laser operation, Silicon, Amplifiers, Semiconductor lasers, Laser applications, Glasses, Mode locking
High-precision micromachining with picosecond lasers became an established process. Power scaling led to industrial
lasers, generating average power levels well above 50 W for applications like structuring turbine blades, micro moulds,
and solar cells. In this paper we report, how a smart distribution of energy into groups of pulses can significantly improve
ablation rates for some materials, also providing a better surface quality. Machining micro moulds in stainless steel, a net
ablation rate of ~1 mm3/min is routinely achieved, e.g. using pulse energy of 200 μJ at a repetition rate of 200 kHz. This
is industrial standard, and demonstrates an improvement by two orders of magnitude over the recent years.
When the energy was distributed to a burst of 10 pulses (25 μJ), repeated with 200 kHz, the ablation rate of stainless steel
was 5 times higher with the same 50 W average power. Bursts of 10 pulses repeated with 1 MHz (5 μJ) even resulted in
an ablation rate as high as 12 mm3/min. In addition, optimized pulse delays achieved a reduction of the surface roughness
by one order of magnitude, providing Ra values as low as 200 nm. Similar results were performed machining silicon,
scaling the ablation rate from 1.2 mm3/min (1 pulse, 250 μJ, 200 kHz) to 15 mm3/min (6 pulses, 8 μJ, 1 MHz). Burst
machining of ceramics, copper and glass did not change ablation rates, only improved surface quality. For glass
machining, we achieved record-high ablation rates of >50 mm3/min, using a new state-of-the-art laser which could
generate >70 W of average power and repetition rates as high as 2 MHz.
