Pulse compression in a gradient-density plasma for a compact exawatt laser

Ultraintense laser pulses are essential tools for experimental study of modern theoretical physics in quantum electrodynamics and lab-astrophysics. It is believed that with exawatt to zettawatt laser pulses, it would be possible to observe the pair-production process in vacuum, Hawking radiation, radiation reaction, and early universe states. However, the conventional chirped pulse amplification (CPA) technique is already close to its technological limitations, mainly due to the vulnerability of compression gratings. Several alternative ideas have been investigated for the past tens of years and particularly, plasma-based schemes for pulse amplification or compression are also emerging as promising methods for the next generation of lasers. Recently we devised a novel idea of compressing a chirped pulse from a critical density plasma with a density gradient exploiting the optical dispersive property of the plasma; in this new scheme, differential reflective paths for different frequency components of the chirped pulse are generated from the density gradient, resulting in the spatial concentration of the photons. From particle-in-cell simulations, compression of a pico-second chirped pulse by more than two hundred times into tens of femtoseconds was observed. Various realistic effects such as collisional heating and density fluctuation were theoretically estimated to reach the conclusion that the compression process will be quite robust in expreiments (under progress). The research has been accepted to a prestigous journal recently [1]. In this presentation, I will talk about the fundamental concept, simulation results, and theoretical estimates relevant to the new idea.