Thin-disk laser multi-pass amplifier

TL;DR

This paper presents a novel multi-pass thin-disk laser amplifier designed for high efficiency and stability, suitable for precise applications like Lamb shift measurements, with innovative mode matching and alignment techniques.

Contribution

The authors developed a multi-pass amplifier with a stable beam propagation scheme insensitive to thermal lens effects and misalignments, enhancing energy scaling and operational stability.

Findings

Achieved a small signal gain of 5 after 8 passes at 400 W pump power.

Laser operated continuously for over 3 months without realignment.

Pointing stability was successfully demonstrated.

Abstract

In the context of the Lamb shift measurement in muonic helium we developed a thin-disk laser composed of a Q-switched oscillator and a multi-pass amplifier delivering pulses of 150 mJ at a pulse duration of 100 ns. Its peculiar requirements are stochastic trigger and short delay time (< 500 ns) between trigger and optical output. The concept of the thin-disk laser allows for energy and power scaling with high efficiency. However the single pass gain is small (about 1.2). Hence a multi-pass scheme with precise mode matching for large beam waists (w = 2 mm) is required. Instead of using the standard 4f design, we have developed a multi-pass amplifier with a beam propagation insensitive to thermal lens effects and misalignments. The beam propagation is equivalent to multiple roundtrips in an optically stable resonator. To support the propagation we used an array of 2 x 8 individually adjustable plane mirrors. Astigmatism has been minimized by a compact mirror placement. Precise alignment of the kinematic array was realized using our own mirror mount design. A small signal gain of 5 for 8 passes at a pump power of 400 W was reached. The laser was running for more than 3 months without the need of realignment. Pointing stability studies is also reported here.