New ideas of plasma-based pulse compression

Exawatt and zettawatt laser pulses have the potential to become transformative scientific tools for exploring the deepest mysteries of our universe. These ultra-high-power laser pulses enable experimental investigation of phenomena such as vacuum boiling, pair production, Hawking radiation, and quantum gravity, offering immense promise for advancing our understanding of fundamental physics. Currently, however, chirped pulse amplification (CPA) technology remains limited to the petawatt scale, primarily due to the material breakdown of compression gratings. Conventional optical approaches have yet to offer viable alternatives. Plasma, as a state of matter already broken down, can withstand extremely intense laser fields without incurring damage. Its robustness under strong fields, along with its optically dispersive characteristics, makes plasma a promising medium for manipulating high-power laser pulses. In this presentation, I introduce a recently proposed concept for pulse compression that employs a high-density plasma with a density gradient. The core idea involves using a near-critical density gradient plasma to create a reflection path difference for photons within a chirped pulse. In this setup, higher-frequency photons penetrate deeper into the plasma and travel longer reflection paths. This allows the photons in the tail of a negatively chirped pulse to catch up with those at the front, resulting in the concentration of the pulse energy into a narrower region. Although this concept remains at the theoretical and modeling stage, it was published in Nature Photonics in 2023 [1], and a proof-of-principle experiment is currently underway. From a theoretical standpoint, research is also ongoing to integrate this density gradient approach with other plasma optics techniques. In this presentation, I will share the current status of the research and outline the future vision of this innovative method. A comparison will also be provided with existing plasma-based schemes, including Raman, Brillouin, and plasma grating approaches. These developments represent critical steps toward achieving compact exawatt and zettawatt laser systems.

[1] Hur et al., Laser pulse compression by a density gradient plasma for exawatt to zettawatt lasers, Nature Photonics 17, 1074 (2023).