  We propose a collective Thomson scattering experiment at the VUV free
electron laser facility at DESY (FLASH) which aims to diagnose warm dense
matter at near-solid density. The plasma region of interest marks the
transition from an ideal plasma to a correlated and degenerate many-particle
system and is of current interest, e.g. in ICF experiments or laboratory
astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The
collective electron plasma mode (plasmon) is revealed in a pump-probe
scattering experiment using the high-brilliant radiation to probe the plasma.
The distinctive scattering features allow to infer basic plasma properties. For
plasmas in thermal equilibrium the electron density and temperature is
determined from scattering off the plasmon mode.
