Page 370 - High Power Laser Handbook

338 So l i d - S t at e La s e r s Ultrafast Lasers in Thin-Disk Geometry 339

other mode-locked laser oscillator technology. Because the average
power is the product of the pulse energy and the repetition rate, decreas-
ing the repetition rate at constant pulse duration leads to higher pulse
energy and peak power. Ultrafast TDLs can generate greater than 10-mJ
pulses directly out of the oscillator, which makes them highly attractive
for applications in material structuring and high-field science. On the
other hand, semiconductor lasers are ideally suited for cost-efficient
mass production due to their epitaxial growth on wafers. Therefore,
they are attractive for such applications as telecommunication or optical
clocking and interconnects, in which a high repetition rate is more
important than high pulse energy. Furthermore, mode-locked VECSELs
cover a wide range of the infrared spectral range—between 0.95 mm and
7
2.01 mm, depending on the semiconductor gain material. This range is
in strong contrast to that of mode-locked solid-state TDLs, which up to
3+
now were only demonstrated with Yb -doped gain materials at a laser
wavelength around (1035 ± 10) nm. This section highlights the funda-
mental reasons for the different operation regimes of VECSELs and
TDLs, which are clearly distinguishable in Fig. 13.6.

Average Power
The upper limit for the average power in mode-locked operation is
the maximum fundamental mode output power in CW operation.
The presence of higher-order modes tends to introduce destabilizing

100 µJ
10 µJ
TDL
1 µJ 1 kW
100 W
100 nJ 10 W
Pulse energy 10 nJ 100 mW
1 W
1 nJ
100 pJ 10 mW
VECSEL
10 pJ 1 mW

1 pJ
100 fJ
1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz
Pulse repetition rate

Figure 13.6 Graphical representation of the different output parameter
regimes for SESAM mode-locked VECSELs and TDLs. The diagonal lines
correspond to constant average output power. The data for the TDL results
were taken from Refs. 12, 14, 33, 43, 58–67; the VECSEL results were
published in Refs. 21, 38, 68–83.