Thomson scattering measurements of heat flow in a laser-produced plasma

Measurements of the electron distribution and heat flow between the critical and ablation surfaces in a laser-produced plasma have been obtained using Thomson scattering. A frequency-quadrupled probe beam was used to obtain Thomson spectra at above-critical densities in a plasma produced by irradiation of solid targets with the fundamental laser light at irradiances of 3 × 10¹⁴ W cm^-2. Comparison of Thomson spectra at the ion acoustic frequency (sensitive to the cold return current) with simulated spectra shows that the data are consistent with Fokker-Planck simulations of the electron distribution function, providing the first direct information on the electron distribution function.