9 June 2011 High-efficiency cyrogenic-cooled diode-pumped amplifier with relay imaging for nanosecond pulses
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We present temperature dependent gain measurements with different Ytterbium doped laser media, such as Yb:YAG, Yb:FP15-glass and Yb:CaF2 in a multi-pass amplifier setup. The temperature of these materials was adjusted arbitrarily between 100K and 300K, while heat removal was realized by transverse cooling. In order to obtain a good beam profile throughout the amplification process, we used an all-mirror based relay imaging setup consisting of a telescope accomplishing a 4f-imaging with a plane mirror in each image plane. The amplification beam is then coupled into the cavity and doing several round trips wandering over the surface of the spherical mirrors. Hence the laser material is placed in one of the image planes, the beam quality of the amplifier was ruled by the intensity profile of the pumping laser diodes consisting of two stacks with 2.5kW peak output power each. Due to the given damage threshold fluence, the output energy of the amplifier was limited to about 1J at a beam diameter of 4.5 mm (FWHM). The seed pulses with a duration of 6 ns were generated in a Yb:FP15-glass cavity dumped oscillator with further amplification up to the 100mJ level by a room temperature Yb:YAG multi pass amplifier. The 1 Hz repetition rate of the system was limited by the repetition rate of the front-end. With Yb:YAG for instance an output energy of 1.1 J with an record high optical to optical efficiency of more than 35% was achieved, which was further increased to 45% for 500 mJ output energy.
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J. Körner, J. Hein, M. Kahle, H. Liebetrau, M. Kaluza, M. Siebold, M. Loeser, "High-efficiency cyrogenic-cooled diode-pumped amplifier with relay imaging for nanosecond pulses", Proc. SPIE 8080, Diode-Pumped High Energy and High Power Lasers; ELI: Ultrarelativistic Laser-Matter Interactions and Petawatt Photonics; and HiPER: the European Pathway to Laser Energy, 80800D (9 June 2011); doi: 10.1117/12.887408; https://doi.org/10.1117/12.887408


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