17 February 2010 Frequency doubling of fiber laser radiation of large spectral bandwidths
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In this work the reduction of conversion efficiency due to spectral bandwidth of fiber laser radiation is investigated. Subsequently, compensation optics to correct the spectral phase mismatching inside the nonlinear crystal is dimensioned and tested. For the experimental study a laboratory fiber laser setup is used consisting of a seed diode and a three stage fiber amplifier. The laser delivers an average output power of up to 100 W at 1 MHz. Even below the Raman threshold the output is far away from Fourier limit, providing a nearly Lorentzian spectral shape and a temporal pulse width of 800 ps. As the bandwidth increases nearly linearly with the pump power of the third amplifier stage, this parameter could be controlled for the experiments. All conversion experiments are conducted with a moderate load of the nonlinear crystals, i.e. intensity less than 150 MW/cm2. Without compensation of the spectral phase mismatch, a maximum conversion efficiency of 15 % is attained for a Type I configuration with a 20mm long LBO crystal. Using the compensation setup 27 W of green light are obtained from 60 W infrared light at a bandwidth of 4.7 nm. Therefore the efficiency rises to 44% at the same load.
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Sebastian Nyga, Sebastian Nyga, Jens Geiger, Jens Geiger, Bernd Jungbluth, Bernd Jungbluth, } "Frequency doubling of fiber laser radiation of large spectral bandwidths", Proc. SPIE 7578, Solid State Lasers XIX: Technology and Devices, 75780P (17 February 2010); doi: 10.1117/12.842075; https://doi.org/10.1117/12.842075

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