Speaker
Description
Gérard Mourou Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Blvd., Ann Arbor, MI 48109, USA
Laser-wakefield plasma accelerators (LWFA) promise compact sources of highly energetic electrons and photons, but for their practical use they need efficient and high repetition rate laser drivers. The current standard is the Ti:sapphire CPA system, which can produce multi-J pulses with bandwidths supporting ~30 fs pulses, but it has low wall plug efficiency (WPE) and ~Hz repetition rates. Fiber laser systems can operate with high WPE at 10’s of kHz and are scalable to high energies and powers using spatial and temporal coherent combining but have bandwidth’s sufficient for only 50-100fs pulses. Additional spectral combining can extend this bandwidth, but by increasing overall complexity of the fiber laser driver. We propose a Nonlinear Coherent Beam Stacking (N-CBS) technique, which could enable achieving several cycle pulses comparable to those of Ti:sapphire, while maintaining multi-kW power and the multi-J energy scalability of coherently combined fiber laser arrays with only a minor increase in the overall complexity of the system and in a compact footprint.
Coherent Pulse Stacking Amplification (CPSA) is critical for reducing spatially-combined fiber laser array sizes by approximately two orders of magnitude. In demonstrated CPSA systems [1] a stacking-burst of stretched pulses extracts nearly-all stored energy from the final amplification stage and is temporally combined (using GTI cavities) into a single stretched pulse for compression to the bandwidth-limit at the system output.
In this paper we show that using a newly discovered Coherent Beam Stacking (CBS), which is a spatial-domain analog of the time-domain Coherent Pulse Stacking (CPS), it is possible to achieve orders-of-magnitude increase in pulse energies with multi-pass cell (MPC) based nonlinear post-compression down to 25-30 fs, while maintaining a compact, 1-3 meter footprint.
Using a specially-designed phase mask, an incident Gaussian beam at the input into an MPC can be transformed into a multi-focal pattern in the Fourier plane of the MPC front mirror. The resultant field contains a pattern of N coherent, equal amplitude, high intensity focused regions reducing the intensity per region by a factor of N for the same pulse energy, while achieving large on-mirror spot sizes. Each roundtrip in, e.g. a gas filled Herriott cell [2], reproduces this pattern in the waist-plane of the optical cavity, and can be transformed back into a diffraction-limited Gaussian beam with another phase mask placed at the MPC output, after a desired number of roundtrips. Because this phase-mask transformed field propagates in an MPC as a single field, all independent random perturbation are homogenized across the multitude of all focal spots, and hence eliminates a need to coherently control their recombination into a single Gaussian beam at the MPC output.
Therefore, this scheme can greatly increase energy handling capability of MPC post-compression, with preliminary results indicating homogeneous spectral broadening of joule level energies in meter length cavities, which can subsequently be compressed using chirped mirrors to durations much shorter than fiber gain bandwidth supports. Implementing this scheme needs only a minor increase in the overall CPSA system complexity. Furthermore, it can be used for spectral broadening of any laser-driver platform, and thus fulfills the general need for such energy scaling-up of a nonlinear post-compression scheme, which was identified in [3].
[1] Rainville, A. et al., (2024). Near-complete extraction of maximum stored energy from large-core fibers using coherent pulse stacking amplification of femtosecond pulses. Optica, 11(11), 1540-1548. doi:10.1364/OPTICA.533803
[2] Kaumanns M, Pervak V, Kormin D, Leshchenko V, Kessel A, Ueffing M, Chen Y and Nubbemeyer T 2018, Multipass spectral broadening of 18 mJ pulses compressible from 1.3 ps to 41 fs, Opt. Lett. 43, 5877
[3] M. F. Kling et al., Roadmap on basic research needs for laser technology, J. Opt. 27 013002 DOI 10.1088/2040-8986/ad8458
| Working group | WG1 |
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