Orbital-angular-momentum-controlled laser pulses with near-relativistic intensity

The spiral phase plate is an essential optical component for the generation of Laguerre-Gaussian laser pulses with doughnut intensity profiles and helical wavefronts. This is due to its extraordinary ability to create and manipulate polarization distributions and orbital angular momentum of laser pulses. Here, we show that Gaussian laser pulses with near-relativistic intensity can acquire orbital angular momentum directly through a fixed-thickness plasma transmission spiral phase plate, whose density increases proportionally to the azimuthal angle around the plasma center. We propose the design for a plasma spiral phase plate and outline how the thickness and density distribution of the plasma determine the orbital angular momentum. We also use three-dimensional particle-in-cell simulations to examine the properties of plasma transmission spiral phase plates, such as orbital angular momentum generation and high-intensity laser pulses manipulation. The simulations suggest that Gaussian laser pulses could be turned into Laguerre-Gaussian laser pulses carrying orbital angular momentum through a $10\text{\ensuremath{-}}\textmu{}\mathrm{m}$ plasma plate, with the conversion efficiency above 90% at high light intensity exceeding ${10}^{17}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. Our scheme offers a method for producing near-relativistic intensity vortex laser pulses with controlled orbital angular momentum, which could significantly advance the development of intense twisted laser pulses in high-field physics. Potential applications include the rotational dynamics of particle clumps, the generation of high-energy particles in plasma accelerators, and the radiation of attosecond pulses radiation with orbital angular momentum.