Improving the brightness of a multi-kilowatt single thin-disk laser by an aspherical phase front correction

Abstract

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.

Power scaling of fundamental-mode thin-disk lasers using intracavity deformable mirrors

“…The applied pressure of three bar at this power level corresponds to a step height on the deformable mirror of about 130 nm. Within the measurement uncertainties, this agrees well with the measured phase distortions of a similar thin-disk setup reported in [4].…”

“…To achieve power scaling to the kW-range, it is therefore necessary to actively compensate for these wavefront deformations. For low-order multimode operation (M 2 < 10), it has been demonstrated that by means of an aspherical intracavity-mirror featuring a static step-like surface shape the aspheric wavefront deformations can be compensated for at a fixed power level [4]. In this way, up to 5 kW of output power from a single disk was demonstrated with a M 2 of 9.2.…”

“…When it comes to fundamental-mode operation, however, even the comparably small residual thermally induced wavefront distortions [4] are limiting power scalability due to their aspheric components induced by the steep temperature gradient at the edge of the pumped region of the laser crystal. Up to now, the highest reported output powers in fundamental-mode operation obtained from a single disk range to about 500 W at beam qualities of M 2 < 1.55 [5], respectively, M 2 < 1.05 [6].…”

250 W single-crystal fiber Yb:YAG laser

“…However, due to the strong signal confinement, their use is limited by the damage threshold of the facets and nonlinear effects such as stimulated Raman scattering, self-phase modulation, and self-focusing in the pulsed regime [1]. The thin-disk technology does not exhibit this limitation in the pulsed regime but suffers from relatively low axial gain limited by amplification of spontaneous emission in the transverse direction gain due to the crystal geometry [2], leading to limited energy per pulse and to complex multipass or regenerative amplifier setups. Finally, the slab technology has recently shown clear competitive advantages with over 1 kW of average output power obtained in the subpicosecond regime and 80 MW peak power [3].…”

Active mirrors for intra-cavity compensation of the aspherical thermal lens in thin-disk lasers

“…Recently, it has been demonstrated, 8 that the aspherical phase distortions introduced by a pumped thin-disk laser crystal can be statically compensated for in a defined power range by the use of an intra-cavity aspheric mirror with a top-hat shaped surface contour matching the mode size on the mirror. Output powers of as high as 5 kW have been achieved from a single disk at M 2 < 10.…”