Preliminary Exploration Of The Refractive Index And Sbs For Pulse CO₂ Laser Effect On Cross-critical Fluid

The thermal physical property of fluid in Near-Critical and supercritical regions is apparently different with the sub-critical region, followed with different optical properties. It should be to study the density and refractive index of the fluid in the sub-critical, near critical and supercritical regions, and to explore the possibilities of its being SBS(stimulated Brillouin scattering) media.By using a pulse CO₂ laser irradiation CO₂ fluid in the optical cell, the phenomena show that the refractive index are smaller when the fluid states are away from the critical point, the refractive index increasing remarkably when the state are not far from the critical point, and the transmission light is divergence when the fluid is right at the critical point; The near critical experimental phenomena are analyzed with scaling law theory.The single-window SBS cell is designed to fill supercritical CO₂ and supercritical C₂H₆ (ethane), calculations and experiments demonstrated that it is safe and reliable when the pressure is lower than 10MPa. The required high pressure is set up by a hydraulic booster and exhaust valve, The needed temperature is got by water circulation.The SBS experiments are done in the sub-critical, supercritical SF₆ and C₂H₆ fluid by using focus pulse CO₂ laser. factors that influence the experimental results such as absorption coefficient, optical breakdown, phonon life and threshold are analyzed.It is analyzed the possibility and effects of SBS in the sub-critical, supercritical fluid,considered that the key to produce SBS in cross-critical fluid is the short phonon lifetime.