Attospiral generation upon interaction of circularly polarized intense laser pulses with cone-like targets

TL;DR

This study demonstrates the generation of attosecond pulses via laser interaction with cone-like targets, revealing spiral harmonic emission and a new numerical method for analyzing coherent synchrotron radiation.

Contribution

It introduces a novel numerical approach to identify the source and direction of attosecond radiation in laser-plasma interactions with cone targets.

Findings

Attosecond pulses are generated with spiral harmonic structures.

The harmonic spectrum is explained by an extended coherent synchrotron emission model.

Harmonics focus into a small volume behind the target.

Abstract

Generation of high intensity attopulses is investigated in cylindrical geometry by using 3D particle-in-cell plasma simulation code. Due to the rotation symmetric target, a circularly polarized laser pulse is considered propagating on the axis of a hollow cone-like target. The large incidence angle and constant ponderomotive pressure leads to nano-bunching of relativistic electrons responsible for the laser-driven synchrotron emission. A numerical method is developed to find the source and direction of the coherent radiation that is responsible for the existence of attopulses. The intensity modulation in the harmonic spectrum is well described by the model of coherent synchrotron emission extended to the regime of higher order \gamma-spikes. The spatial distribution of the higher harmonics resembles a spiral shape which gets focused into a small volume behind the target.