Directly determining orbital angular momentum of ultrashort Laguerre-Gauss pulses via autocorrelation measurement

TL;DR

This paper introduces a novel method using autocorrelation measurement based on second-harmonic generation to determine the orbital angular momentum of ultrashort Laguerre-Gauss pulses, enabling full spatial characterization.

Contribution

It extends the autocorrelation technique to measure both azimuthal and radial indices of ultrashort LG pulses, enhancing laser pulse characterization capabilities.

Findings

Successfully measured orbital angular momentum of ultrashort LG pulses

Unambiguously determined full spatial structure including azimuthal and radial indices

Demonstrated experimental feasibility of the method

Abstract

Autocorrelation measurement based on second-harmonic generation (SHG), the best-known technique for measuring the temporal duration of ultrashort pulses, could date back to the birth of ultrafast lasers. Here, we propose and experimentally demonstrate that such well-established technique can also be used to measure the orbital angular momentum of ultrashort Laguerre-Gauss (LG) pulses. By analysing the far-field pattern of the SHG signal, the full spatial structure of ultrashort LG pulses, including both azimuthal and radial indices, are unambiguously determined. Our results provide an important advancement for the well-established autocorrelation technique by extending it to reach its full potential in laser characterization, especially for structured ultrashort pulses.