46 Photonics Spectra June 2016 www.photonics.com
To ful;ll current and future customer
needs in the ultrashort pulse (USP) laser
micromachining market, faster processing
time is critical. In only the last few years
the average power of these lasers has risen
continuously, reaching an average power
of 1 k W or more. The higher output power
allows for an increased pulse repetition
rate (PRR), while maintaining the necessary pulse energy for efficient material ablation. This means more ablation per second, strongly increasing throughput.
However, with a highly increased PRR
comes a new challenge: It’s increasingly
difficult to avoid the accumulation of too
many pulses on one spot of the work-
piece. The ultrahigh PRR of modern laser
systems simply exceeds the deflection
capability of galvanometer-based scan-
ning systems. Resonant and other scan-
ner technologies, reach extremely high
scan speeds of more than 1000 m/s, but
they suffer from a sinusoidal varying scan
speed, leading to an inconsistent spot dis-
tance on the workpiece.
To overcome this drawback, the non-
linearity of the resonant scanners can be
compensated by a dynamically and syn-
chronously adaptable PRR. In this way
a uniform spot distance across the whole
scanning range becomes possible. Modern
laser systems with dynamically adaptable
pulse repetition rates, combined with ul-
trafast resonant scanners, are great candi-
dates for breaking through the current lim-
itations of high-speed micromachining.
USP laser systems with dynamic PRRs
have shown great potential in other appli-
cations, like speeding up the processing of
narrow curves1, or homogenizing the abla-
tion with a laser turning machine2. In that
case, a variable PRR in the kHz range is
achieved by picking pulses out of a pulse
train with a given base PRR. An impor-
tant consideration for future applications
is whether it is possible to scale this ap-
proach to the MHz range.
The following addresses the require-
With the power of ultrashort pulse laser systems on the rise,
achieving dynamically and synchronously adaptable pulse repetition rates
in the MHz range is the key to higher throughput.
BY FLORIAN HARTH, THOMAS HERRMANN, BERNHARD HENRICH AND JOHANNES A. L‘HUILLIER
PHOTONIK-ZENTRUM KAISERSLAUTERN EV AND RESEARCH CENTER OPTIMAS
Ultrashort Pulse Laser
Images courtesy of Photonik-Zentrum Kaiserslautern eV.
Initial lab setup for ultrafast
micromachining with a
resonant scanner and
the new laser system.