Diffractive multi-beam surface micro-processing using 10 ps laser pulses

A high repetition rate picosecond laser system is combined with a spatial light modulator (SLM) for diffractive multiple beam processing. The effect of the zero order beam is eliminated by adding a Fresnel zone lens (FZL) to defocus the un-diffracted beam at the processing plane. Chromatic dispersion, which is evident with a large bandwidth femtosecond pulses leading to the problem of distorted hole shape is eliminated due to the much narrower spectral bandwidth, 0.1 nm at 10 ps pulselength, resulting in highly uniform intensity spots, independent of diffraction angle. In addition, high-throughput processing is demonstrated by combining the high power laser output, 2.5 W at λ ≈ 1064 nm and fast repetition rate, f ≈ 20 kHz with P > 1.2 W diffracted into 25 parallel beams. This has the effect of creating an “effective” repetition rate of 500 kHz without restrictive scan speeds.