Velocity measurements of a high-intensity laser-driven hot plasma using Doppler shift spectroscopy

Doppler shift-based spectroscopy is a robust and well understood technique used to characterize rapidly evolving processes. The principle has been recently applied to high-intensity laser-plasma interaction experiments to characterize ultra-fast laser-driven hot plasma dynamics (with velocities of the order of 10⁵m/s). Adding a high spatial characterization component to the measurements would improve our understanding of plasma motion in the pico-second time scale.

Preliminary experimental results, showing 2D resolved velocity measurements of an expanding plasma, from an experiment performed at Colorado State University using compressed pulses from the ALEPH laser (~45fs) are presented. Intensities of the order of 10¹⁸W/cm² were used to generate an expanding plasma while a much less intense, frequency doubled (400nm), probe beam (10¹¹W/cm²) was used to measure the Doppler shift of the plasma surface corresponding to ~7×10²¹ particles per cm^-3.

The data presented was obtained using a new customized fiber-based imaging spectrometer design. The latter permitted to collect data from 21 sample points distributed over a 100um×100um plasma area, corresponding to a spatial resolution of ~22μm. This diagnostic and the details of the spatially-resolved measurement will be described as a novel technique to provide validation on plasma evolution as a function of time with a pico-second resolution.