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High-average power second harmonic generation of femtosecond fiber lasers

: Hädrich, S.; Rothhardt, J.; Eidam, T.; Gottschall, T.; Limpert, J.; Tünnermann, A.


Dawson, J.W. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Fiber Lasers VIII: Technology, Systems, and Applications : 22.-26.1.2011, San Francisco, California, USA, SPIE Photonics West
Bellingham, WA: SPIE, 2011 (Proceedings of SPIE 7914)
ISBN: 978-0-8194-8451-2
Paper 79140S
Conference "Fiber Lasers - Technology, Systems, and Applications" <8, 2011, San Francisco/Calif.>
Fraunhofer IOF ()
fiber laser; ultrafast optics; nonlinear optics; frequency conversion; frequency doubling; high power

We present second harmonic generation of a high average power, high energy femtosecond Yb doped fiber chirped pulse amplifier. This system is operated at various repetition rates at a central wavelength of 1040 nm. After two pre-amplification stages a main amplifier is used to achieve the required pulse energy for efficient second harmonic generation. It is comprised of a 1.2 m long photonic crystal fiber with a mode field diameter of 45 ?m. A dielectric grating based compressor is used for compression to a pulse duration of about 406 fs. Second harmonic generation is then achieved in a 500 ?m thick BBO crystal. The conversion efficiency of the second harmonic generation remained almost constant at >60 % for all repetition rates and average power levels. At 5.25 MHz the highest average power of 135 W at 520 nm was achieved. In addition this comes with an excellent beam quality which is validated by a measured M2 < 1.2.