High-power lasers have unlocked new regimes of strong-field physics and continue to push the boundaries of science and technology. Progress further into the petawatt range would benefit not only from more pulse energy but also from shorter pulse durations to increase peak power. However, the optical parametric chirped pulse amplifiers that are typically used to boost the energy must be seeded with pulses of sufficient spectral bandwidth to support the required duration. A common method of obtaining the necessary bandwidth is through self-phase modulation in noble gas; this process is coherent, ensuring that pulses can be compressed after amplification. In this paper, the authors spectrally broaden pulses in argon confined to a single, meter-long hollow silica waveguide—not a fiber in the conventional sense of the word, but a straight capillary that guides by grazing-incidence reflection. By optimizing the diameter of the hollow core, they achieve in a single stage of modulation the broadest-bandwidth high-energy pulses around a wavelength of 1 micron, capable of being compressed to below 10 femtoseconds. For aficionados of the field, this claim can be set apart from work carried out in photonic crystal fiber which has achieved much broader bandwidths at somewhat lower pulse energies. The authors suggest that their source is suitable as the front-end of a 1-petawatt laser system of the future.
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