Raster Thomson scattering in large-scale laser plasmas produced at high repetition rate

TL;DR

This paper demonstrates high-repetition-rate optical Thomson scattering measurements of electron density and temperature in large laser-produced plasmas, enabling spatially resolved diagnostics with automated positioning.

Contribution

It introduces a high-repetition-rate Thomson scattering diagnostic capable of spatially resolved measurements in large-scale plasmas, a significant advancement over previous single-shot methods.

Findings

Measured electron densities around 4×10^{16} cm^{-3}

Observed transition from collective to non-collective scattering

Achieved density measurements within 10% accuracy via Raman calibration

Abstract

We present optical Thomson scattering measurements of electron density and temperature in a large-scale (~2 cm) exploding laser plasma produced by irradiating a solid target with a high energy (5-10 J) laser pulse at high repetition rate (1 Hz). The Thomson scattering diagnostic matches this high repetition rate. Unlike previous work performed in single shots at much higher energies, the instrument allows point measurements anywhere inside the plasma by automatically translating the scattering volume using motorized stages as the experiment is repeated at 1 Hz. Measured densities around 4$\times 10^{16}$ cm$^{-3}$ and temperatures around 7 eV result in a scattering parameter near unity, depending on the distance from the target. The measured spectra show the transition from collective scattering close to the target to non-collective scattering at larger distances. Densities obtained by fitting the weakly collective spectra agree to within 10% with an irradiance calibration performed via Raman scattering in nitrogen.