Page 286 - High Power Laser Handbook

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

HR Laser disc
HR
AOM
T = 10%
Figure 10.23 Resonator design of the q-switched laser. AOM: acousto-optic
modulator. (Courtesy of Dausinger und Giesen Gmb)

10.7.1 Q-Switched Operation of the Thin-Disc Laser
An easy way to reach high pulse energies with the thin-disc concept
is active q-switched operation. 55,56 Figure 10.23 shows a possible
design for a q-switched thin-disc laser. The resonator is folded so that
a short resonator length could be realized with a large mode area in
the disc for fundamental mode operation. Q-switching is performed
by a quartz acousto-optic modulator (AOM). Figure 10.24 shows the
pulse energy as function of the repetition rate for the active laser
material Yb:YAG. Stable operation can be achieved with repetition
rates up to 13 kHz; for higher repetition rates bifurcations of the pulse
energy may be observed. The maximum pulse energy is 18 mJ at
1-kHz repetition rate and the maximum average power is 64 W at
13 kHz, which corresponds to an optical efficiency of 34 percent. The
beam propagation factor M² was better than 2 in all cases. 56

18
16 190 W pump power
160 W pump power
14 140 W pump power
110 W pump power
12
Pulse energy (mJ) 10 8 60 W pump power
80 W pump power

4 6

2

0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Repetition rate (kHz)
Figure 10.24 Pulse energy of the q-switched thin-disc laser as function of
the repetition rate for different pump power levels.