Thesis or Dissertation Thin-disk lasers based on Yb3+-doped ceramics

中尾, 博明  ,  ナカオ, ヒロアキ  ,  Nakao, Hiroaki

pp.1 - 130 , 2015-03-25 , The University of Electro-Communications
Thin-disk laser is one of the key technologies in modern high power laser fields. It enables to realize high beam quality under high average power operation owing to its almost negligible thermo-optic distortions. Recently, various thin-disk laser sources based on single crystals have been investigated, whereas only a few thin-disk lasers have been demonstrated with ceramics. In this thesis, the performances of the thin-disk lasers are evaluated. These are based on Yb3+-doped ceramics, especially Yb3+-doped Lu3Al5O12 (LuAG) and Yb3+- doped Lu2O3 ceramics which are expected to have advantages in high power and highly efficient operations. The spectroscopic properties and the thermal properties of the ceramics are measured systematically. Using the Yb:LuAG ceramic with a doping concentration of 10 at.% and a thickness of 150μm, a high power and a highly efficient thin-disk laser operation is demonstrated in a continuous wave (CW) regime. The maximum output power reaches 166 W with the maximum slope efficiency and the maximum optical efficiency of 72% and 60%, respectively. The efficiencies are almost comparable to those of the thin-disk lasers based on Yb:LuAG single crystals. These results show that ceramics are one of the best gain media for the thin-disk lasers as is the case in the single crystals. The Yb:Lu2O3 ceramics with a doping concentration of 3 at.% are contacted on copper heat sinks with new contacting schemes. The thin-disk lasers based on Yb:Lu2O3 ceramics were demonstrated in a CW regime. The maximum slope efficiency of 61% and the maximum optical efficiency of 45% are achieved with 300μm-thick ceramic thin-disk. Any damages of the disks and instabilities are not observed in those operation parameters. Additionally, the high damage threshold of the disks (at least 6kW/cm2) is expected from the thermographical measurements of the disks. These results denote that the new schemes can be used for high power lasers.

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