For spectroscopy on muonic helium, we developed a thin-disk laser with an output pulse energy of 147 mJ capable of stochastic triggering (< 500 Hz) with a beam quality of M² = 1.04. We reached these values by implementing Fourier transform propagation from disk to disk. This architecture is passively compensating for phase front distortions caused by thermal lensing in the thin disk. The amplifier was not only very stable against thermal lens effects but was also forgiving misalignment of the disk. Indeed, it was operated for 3 months without realignment.
Our design utilizes the gain profile of the active medium (effective soft aperture) to provide transversal mode filtering. As a result, the beam remains in the TEM00 mode during propagation in the amplifier. This implies that modeling of its propagation does not require techniques for higher-order mode propagation. Soft apertures can simply be modeled as lenses with imaginary focal length. We modeled the misalignment related losses for two different multi-pass amplifier designs reproducing the measured behavior.
We also realized a simple control system to correct for tilt misalignment of the active medium. Only two servo-controlled folding mirrors inside the amplifier were sufficient to stabilize the beam position of all (eight) passes on the active medium. This active stabilization reduced the sensitivity (decrease of output energy) to tilts of the active medium by a factor of 10 compared to the multi-pass amplifier without active stabilization.
We present a multi-pass amplifier which passively compensates for distortions of the spherical phase front occurring in the active medium. The design is based on the Fourier transform propagation which makes the output beam parameters insensitive to variation of thermal lens effects in the active medium. The realized system allows for 20 reflections on the active medium and delivers a small-signal gain of 30 with M<sup>2</sup> = 1.16. Its novel geometry combining Fourier transform propagations with 4f-imaging stages as well as a compact array of adjustable mirrors allows for a layout with a footprint of 400 mm × 1000 mm.
We present a frequency selective optical setup based on a Gires-Tournois interferometer suitable to enforce single-frequency operation of high power lasers. It is based on a birefringent Gires-Tournois interferometer combined with a λ/4 plate and a polarizer. The high-reflective part of the Gires-Tournois interferometer can be contacted to a heat sink to obtain efficient cooling (similar cooling principle as for the active medium in thin-disk lasers) enabling power scaling up to output powers in the kW range.