\emph{In situ} measurement of three-dimensional ion densities in focused femtosecond pulses

TL;DR

This paper presents a method for three-dimensional in situ imaging of ion densities in the focus of ultrashort laser pulses, enabling detailed analysis of ionization processes and beam profiles with micron-scale resolution.

Contribution

It introduces a novel in situ ion imaging technique that captures 3D ion distributions in the focus of femtosecond pulses, surpassing traditional spatial averaging methods.

Findings

Achieved ~3 μm and ~12 μm spatial resolution in transverse directions.

Successfully imaged and analyzed the intensity profile of a Hermite-Gaussian beam.

Demonstrated the technique's utility for studying ionization and beam quality.

Abstract

We image spatial distributions of Xe$^{q+}$ ions in the focus of a laser beam of ultrashort, intense pulses in all three dimensions, with a resolution of $\sim$3 $\mu$m and $\sim$12 $\mu$m in the two transverse directions. This allows for studying ionization processes without spatially averaging ion yields. Our \emph{in situ} ion imaging is also useful to analyze focal intensity profiles and to investigate the transverse modal purity of tightly focused beams of complex light. As an example, the intensity profile of a Hermite-Gaussian beam mode HG$_{1,0}$ recorded with ions is found to be in good agreement with optical images.