We report on results obtained with an aspherical mirror to compensate for the phase front aberrations of a cw thin-disk laser with a single disk in the resonator. A record output power of 5 kW with a beam quality suitable for laser cutting (beam propagation factor M2=9.2) has been achieved.

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We present the efficient propagation of a nearly diffraction-limited laser beam with a continuous wave power of 800 W through a multi-mode step-index delivery fiber with a core diameter of 30 µm and a numerical aperture of 0.056. The M2-value was measured to be 1.35 after 100 m of this passive fiber. This is an important advance as the delivery fiber length for high-brightness beams in the kilowatt range is usually limited to a few meters by the onset of nonlinear effects. For this demonstration a single-mode MOPA system was set-up consisting of a fiber oscillator and two amplifier stages. This source was coupled into the delivery fiber through a 500 mm long mode field adapter.

We present the nearly diffraction-limited propagation of 800 W of cw laser power through 100 m of delivery fiber having a core diameter of 30 µm. The laser source was a single-mode MOPA consisting of a fiber oscillator and two amplifier stages and was matched to the delivery fiber through a 500 mm long taper. At a maximum power of 800 W, a M 2 value of 1.35 was measured after 100 m of passive fiber. A minor Stokes-shifted spectral content was observed above 780 W.

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