Spectral broadening of 2 mJ femtosecond pulses in a compact air-filled convex-concave multi-pass cell

TL;DR

This paper demonstrates a simple, compact, air-filled convex-concave multi-pass cell that achieves spectral broadening of high-energy femtosecond pulses, enabling efficient pulse compression with minimal damage and low cost.

Contribution

It introduces the first convex-concave MPC design operated in air for high-energy pulses, simplifying spectral broadening and compression setups.

Findings

Spectral broadening from 2.1 nm to 24.5 nm at 100 kHz

Pulse compression down to 134 fs

High transmission efficiency of 96%

Abstract

Multi-pass cell (MPC) based temporal pulse compressors have emerged in the last years as a powerful and versatile solution to the intrinsic issue of long pulses from Yb-based high-power ultrafast lasers. However, the spectral broadening of high-energy (typically more than 100 uJ) pulses has only been realized in complex setups, i.e., in large and costly, pressure-controlled vacuum chambers to avoid strong focusing, ionization, and damage on the mirrors. Here, we present spectral broadening of 2 mJ pulses in a simple and compact (60 cm long) multi-pass cell operated in ambient air. Instead of the traditional Herriott cell with concave-concave (CC/CC) mirrors, we use a convex-concave (CX/CC) design, where the beam stays large at all times allowing both to minimize damage and operate in ambient air. We demonstrate spectral broadening of 2.1 mJ pulses at 100 kHz repetition rate (200 W of average power) from 2.1 nm (pulse duration of 670 fs) to a spectral bandwidth of 24.5 nm, supporting 133 fs pulses with 96% transmission efficiency. We show the compressibility of these pulses down to 134 fs, and verify that the spectral homogeneity of the beam is similar to previously reported CC/CC designs. To the best of our knowledge, this is the first report of a CX/CC MPC compressor, operated at high pulse energies in air. Because of its simplicity, small footprint and low cost, we believe this demonstration will have significant impact in the ultrafast laser community.