Page 364 - High Power Laser Handbook

332 So l i d - S t at e La s e r s Ultrafast Lasers in Thin-Disk Geometry 333

VECSEL * Solid-State TDL
In Ga As/GaAs 10% Yb:YAG
0.13 0.87
Output Parameters
Average output power 2.1 W 80 W
Repetition rate 4 GHz 57 MHz
Pulse duration 4.7 ps 703 fs
Pulse energy 0.53 pJ 1.4 µJ
Pump power 18.9 W 360 W
Opt.-to-opt. efficiency 11% 22%
Setup Parameters
Total disk thickness ~6 µm ~105 nm
Active region thickness ~1 µm 100 µm
Pump spot diameter 350 µm 2.8 mm
Pump density 19.6 kW/cm 2 5.8 kW/cm 2
Outcoupling rate 2.5% 8.5%
Pump wavelength 808 nm 941 nm
Laser wavelength 957 nm 1030 nm
Quantum defect 15.6% 8.6%
Material Parameters
Upper state lifetime ~1 ns ~1 ms
Absorption coefficient 10 cm –1 10 cm –1
4
Absolute thermal 8 K/W 3.3 K/W
resistance *
2
2
Normalized thermal 0.77 Kmm /W 20.6 Kmm /W
resistance **
Gain cross sections ~10 –16 cm 2 ~10 –21 cm 2
* The data for the VECSEL were taken from Refs. 21, 38–41; those for the solid-
state TDL are from Refs. 42–44.
** The normalized thermal resistance is independent of the pumped area, while the
absolute thermal resistance value is obtained by dividing the normalized thermal
resistance by the pumped area, which is much smaller in the case of a typical
VECSEL.
Table 13.1 Comparison of Output, Setup, and Material Parameters of the
VECSEL and of the Yb:YAG-Based TDL with the Currently Highest-Average
Output Power in Mode-Locked Operation