A compact 20-pass thin-disk multipass amplifier stable against thermal lensing effects and delivering 330 mJ pulses with $\bf{M^2 < 1.17}$

TL;DR

This paper presents a compact, stable 20-pass Yb:YAG thin-disk multipass amplifier that delivers high-energy, high-quality pulses with minimal thermal lensing effects, suitable for demanding laser applications.

Contribution

The design introduces a novel concatenation of stable resonator segments with Fourier transform and 4f-imaging stages to mitigate thermal lensing and improve beam quality.

Findings

Delivers 330 mJ pulses at 1030 nm with M^2 < 1.17.

Achieves small signal gain of 20 and gain of 6.9 at maximum energy.

Stable against thermal lensing effects due to innovative optical design.

Abstract

We report on an Yb:YAG thin-disk multipass amplifier delivering 50 ns long pulses at a central wavelength of 1030 nm with an energy of 330 mJ at a repetition rate of 100 Hz. The beam quality factor at the maximum energy was measured to be $\text{M}^2 = 1.17$. The small signal gain is 20, and the gain at 330 mJ was measured to be 6.9. The 20-pass amplifier is designed as a concatenation of stable resonator segments in which the beam is alternately Fourier transformed and relay-imaged back to the disk by a 4f-imaging optical scheme stage. The Fourier transform propagation makes the output beam robust against spherical phase front distortions, while the 4f-stage is used to compensate the thermal lens of the thin-disk and to reduce the footprint of the amplifier.