the amplification of these pulses, with
energies in the range of a few pJ, to the
required µJ pulse energies. In general, a
regenerative amplifier would provide the
necessary amplification, but the high and
dynamical variable PRR would get lost. So
the most feasible way is a combination of a
semiconductor oscillator and a linear amplifier chain, consisting, for example, of a
fiber pre-amplifier and a solid-state power
amplifier. A combination of the best concepts derived from different state-of-the-art technologies will do the job.
USP semiconductor lasers with PRRs between 1 to 10 GHz and ultrafast pulse picking were developed years ago3 and since
then the technology has matured. A mode-locked semiconductor laser oscillator with
a base PRR of 4. 3 GHz, for instance, was
developed by FBH Berlin4. Mode locking
was achieved in a monolithic Fabry-Perot
diode laser resonator. Pulse picking was
done by ultrafast pumping of a subsequent
waveguide preamplifier beyond the transparency level and back. Gate widths of 200
ps were achieved, short enough for picking single pulses out of the 4.3-GHz pulse
Ultrashort Pulse Lasers Tech Feature
Figure 3. Variation of the repetition rate as the resonant scanner scans the workpiece.
As the scan-speed decreases at the turning points, a lower PRR is necessary to maintain the spot distance
∆s. Only discrete values are possible for a low base PRR (a). Discrete repetition rates lead to large deviations
from the desired spot distance ∆s = v/PRR, where v is the continuously varying scan-speed (b).