Complete temporal characterisation of asymmetric pulse compression in a laser wakefield

TL;DR

This paper provides a comprehensive experimental analysis of the temporal shape and asymmetric compression of ultrashort laser pulses in a laser wakefield, revealing how plasma conditions influence pulse duration and chirp.

Contribution

It uniquely measures the pulse phase using FROG and correlates pulse compression with plasma parameters, advancing understanding of laser-plasma interactions.

Findings

Pulse duration decreases linearly with plasma length and density.

Asymmetric pulse compression exhibits positive chirp due to photon acceleration.

Measured pulse characteristics align with theoretical predictions of group velocity variation.

Abstract

We present complete experimental characterisation of the temporal shape of an intense ultrashort 200-TW laser pulse driving a laser wakefield. The phase of the pulse was uniquely measured using (second order) frequency resolved optical gating (FROG). The pulses are asymmetrically compressed, and exhibit a positive chirp consistent with the expected asymmetric self-phase modulation due to photon acceleration/deceleration in a relativistic plasma wave. The measured pulse duration decreases linearly with increasing length and density of the plasma, in quantitative agreement with the intensity dependent group velocity variation in the plasma wave.