Enhancement of brightness of high-order harmonics with elliptical polarization from near-critical density plasmas irradiated by an ultraintense laser pulse

Bright extreme ultraviolet (XUV) sources with elliptical polarization are powerful tools for investigating the electronic and magnetic properties of materials. Here we show that in the regime of relativistic electrons spring, it is possible to generate a source of elliptically polarized attosecond XUV pulses by a circularly polarized laser pulse interacting with near-critical density plasmas. Particle-in-cell simulations indicate that compared with a conventional overdense plasma regime, the attosecond pulse intensity may be increased by up to one order of magnitude in a near-critical density plasma system.