Laser pulse compression by a density gradient plasma for exawatt to zettawatt lasers

We propose a new method of compressing laser pulses to ultra-high powers based on spatially varying dispersion of an inhomogeneous plasma. Here, compression is achieved when a long, negatively frequency-chirped laser pulse reflects off the density ramp of an over-dense plasma slab. As the density increases longitudinally, high frequency photons at the leading part of the laser pulse penetrate more deeply into the plasma region than lower frequency photons, resulting in pulse compression in a similar way to that by a chirped mirror. Proof-of-principle simulations carried out using a one-dimensional (1D) and quasi-3D particle-in-cell (PIC) simulation codes predict compression of a 2.35 ps laser pulse to 10.3 fs, a ratio of 225. As plasma is robust and resistant to damage at high intensities, unlike solid-state gratings commonly used in chirped-pulse amplification (CPA), the method could be used as a compressor to reach exawatt or zettawatt peak powers.