Intense harmonics with time-varying orbital angular momentum from relativistic plasma mirrors

TL;DR

This paper demonstrates the generation of intense high-order plasma surface harmonics with a time-varying orbital angular momentum (self-torque) using two laser beams with different OAMs and a plasma mirror, opening new avenues in ultrafast spectroscopy.

Contribution

The study introduces a novel method to produce harmonics with a time-varying OAM by combining two laser beams with different OAMs and analyzing their interaction with plasma mirrors.

Findings

Harmonics with OAM spanning nl1 to nl2 can be generated.

The process produces intense self-torqued harmonics.

Potential applications in ultrafast spectroscopy.

Abstract

In this work using three-dimensional particle-in-cell simulations and analytical considerations we demonstrate intense high-order plasma surface harmonics carrying a time-varying orbital angular momentum (OAM) -- the self-torque. We show that by using two laser beams with different OAMs $l_1$ and $l_2$ and a certain delay between each other and shooting them obliquely on an overdense plasma target, one can generate harmonics with OAM spanning $nl_1$ to $nl_2$, where $n$ is the order of the harmonic. Such intense self-torqued harmonics can offer new possibilities in ultrafast spectroscopy.