Page 285 - High Power Laser Handbook

254 So l i d - S t at e La s e r s Thin-Disc Lasers 255

laser power levels with nearly fundamental mode properties will be
possible in future.
With the potential of very high output power levels for the funda-
mental mode, it is possible to operate thin-disc lasers also in single
frequency operation. 43,44 To achieve this, it is necessary to use a birefrin-
gent filter and one or two uncoated etalons inside the fundamental
mode resonator. With such resonators, up to 98-W single frequency
43
power has been demonstrated. In addition, the laser’s wavelength
can be tuned over a wide spectral range (1000–1060 nm for Yb:YAG) by
tuning the birefringent filter. 5,43–46
Another interesting feature is resonator’s internal doubling of the
laser frequency for covering the visible spectral range with high
efficiency. This can be successfully demonstrated with different laser
materials. With Yb:YAG the wavelength tunability between 500 and
530 nm, maximum power around 515 nm could be shown; 50-W
green output power is commercially available. For Nd:YVO 4 18,19 more
than 12 W can be demonstrated at 532-nm wavelength and more than
3 W can be demonstrated at 457 nm (doubling of the quasi-three-level
transition at 914 nm). For Nd:YAG more than 1 W at 660 nm was
achieved when doubling the 1320 nm transition.

10.7 Thin-Disc Laser in Pulsed Operation
In addition to the outstanding properties of the thin-disc laser’s
design for CW operation, it is also well suited for pulsed laser sys-
tems, especially if high average output power is demanded. Until
recently, pulsed thin-disc laser systems had been developed and
demonstrated for the nanosecond-, picosecond-, and femtosecond-
pulse duration regime. All systems showed an excellent beam quality
and a high efficiency.
In Ursula Keller’s group at the ETH Zurich high average power
fs-oscillators have been developed, which are described in more
detail in Chap. 13. 47–51 It has been demonstrated that with the thin-
disc laser design, high output powers are possible down to pulse
52
durations of 220 fs, especially with the use of Yb:Lu O and
2
3
53
Yb:LuScO . An exhaustive overview of possible laser materials and
3
the achieved results with mode-locked thin-disc lasers can be found
in a recent paper. The mode locking of thin-disc lasers with semi-
54
conductor saturable absorbers (SESAM) is a very elegant approach to
exploit the scaling behavior of both concepts, as the SESAM concept
also can be scaled by increasing the active area. This advantage is
already transformed to an industrial product, a mode-locked thin-disc
laser with 800 fs pulse duration and 50 W output power available
from Time–Bandwidth products.
In the following sections the results for q-switched lasers, cavity
dumped lasers and for pulse laser amplifiers are discussed in more
detail.