Characteristics of the polarisation of a signal of four-photon scattering of light in an optical-breakdown plasma

An experimental study was made of the polarisation properties of a signal resulting from four-photon scattering of light in an optical-breakdown plasma. The excitation of the atomic system altered the polarisation of the four-photon scattering signal. An experimental system for coherent ellipsometry of quasiresonant excited atomic systems, sensitive to the contribution of the states in the continuous spectrum, is proposed.