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Description
Coherently combined fiber lasers offer a promising route to scalable drivers for LPAs and high-intensity laser–matter interactions. Coherent pulse stacking amplification (CPSA), based on time-domain coherent combining of pulse bursts using Gires–Tournois interferometers (GTIs), provides a scalable approach for energy scaling. In this technique, a burst of temporally stretched pulses is coherently combined into a single high-energy pulse, followed by compression in a diffraction-grating-based compressor.[1] As an extension of chirped pulse amplification (CPA), CPSA offers a viable pathway toward multi-joule femtosecond laser drivers with excellent control over pulse shaping and scalability. However, in CPA-based CPSA fiber systems, reaching sub-50-fs compressed pulse durations typically requires an additional spectral-broadening stage, because the amplified bandwidth is constrained by the gain bandwidth and gain narrowing of the amplifier chain.
In this work, we propose and investigate a complementary coherent stacking approach based on gain-managed nonlinear (GMN) fiber amplification. Unlike conventional CPA-based energy scaling, GMN amplification simultaneously provides energy extraction and nonlinear spectral broadening, enabling the generation of high-energy, broadband ultrashort pulses directly from the fiber amplifier. The amplified pulse bursts are subsequently coherently stacked using GTI cavities and compressed with a compact compressor to generate high-energy pulses with sub-50-fs femtoseconds durations. This approach enables more compact system architectures while preserving scalability in both pulse energy and average power.
We found that efficient coherent stacking of GMN-amplified bursts requires careful control of pulse-to-pulse variations in their temporal, spectral, and phase profiles. These variations, driven by gain saturation and nonlinear propagation across the burst, can significantly reduce stacking efficiency if left uncompensated. Tailored input burst shaping compensates for gain-dynamics-induced distortions and preserves the pulse-to-pulse similarity required for efficient stacking of broadband, high-pulse-energy GMN bursts. This enables CPSA-comparable pulse energies and sub-50-fs compressed pulse durations without a separate spectral-broadening stage, or a large diffraction-grating compressor stage need for CPA.
As an experimental basis for this architecture, we first achieved record-high single-pulse energies in GMN amplification from a large-mode-area fiber, generating 5 µJ, 46 fs and 8 µJ, 60 fs compressed pulses at a 1 MHz repetition rate , and further extended the system to burst operation with 125 µJ, 50 fs compressed burst pulses at a 100 kHz burst repetition rate. These results establish GMN amplification as a broadband, high-pulse-energy front end for temporal coherent stacking. Simulations show that tailored input burst shaping can mitigate gain-saturation-induced pulse-to-pulse distortions and enable 1–5 mJ stackable burst pulses. Further energy and average-power scaling can be achieved through spatial coherent combination of multiple GMN amplification channels. This architecture therefore offers a promising route toward compact, high repetition rate femtosecond LPA drivers.
[1] Rainville, Alexander, et al. "Near-complete extraction of maximum stored energy from large-core fibers using coherent pulse stacking amplification of femtosecond pulses." Optica 11.11 (2024): 1540-1548.
| Working group | WG1 |
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