Thomson scattering measurements of the plasma density and temperatures in the region of shock collision. Spectra of Thomson scattering off electron plasma waves (a, c) and ion acoustic waves (b, d). Then, (a) and (b) show the spectra profiles, corresponding to 15 ns, while (c) and (d) show the temporal evolution of the scattering spectra over a time period from 13 ns to 16 ns for the electron plasma and ion acoustic waves, correspondingly. Black solid lines (in a and b) are for experimental data profiles, while red solid lines are for theoretical spectra, composed of a superposition of narrow (black dotted lines) component relative to the ambient medium, having density 1.5 × 10¹⁸ cm³, electron temperature 100 eV, ion temperature 200 eV, and broad (black dashed lines) component relative to the piston plasma, having density 6 × 10¹⁸ cm³, electron temperature 300 eV, ion temperature 100 eV. The ratio between the magnitudes of the narrow and broad components is 3.5. We note that the deep central dip in the experimental spectra (a, b) and the white vertical region in the streak-camera images (c, d) is related to a filter (a black aluminum stripe) which is positioned right before the entrance of the two streak cameras (recording respectively the light scattered off the electron and ion waves). This filter is used to block the very intense and unshifted laser wavelength (the Rayleigh-scattered light), which otherwise would saturate the cameras. Thus, no signal is recorded in this zone, which is materialized by the gray dashed box.