Study On Density And Refractive Index Of Near-critical Fluid

The property of Near-Critical Fluid(NCF) is markedly influenced by temperature and pressure. Tiny change of temperature or pressure may make great change of density and other characteristics. This study is committed on the connection of density and refractive index with temperature and pressure, the optical properties of NCF, so as to find an available way to tuning, compress the pulse duration and to improve the quality of laser beam.The needed high pressure is set up by a hydraulic supercharger, which can adjust the upper limit of pressure, and the pressure could fall down by a valve. The needed temperature is realized by water circulation. Using high pure fluid to make sure the pureness of medium. Adding a filter in the pipeline eliminate the possibility of hydraulic oil and other impurity getting into the optical cell. Using pure fluid to flush cell and replace the air inside, so that we can insure the pureness of the medium.Record the phenomena of Carbon dioxide and Sulfur fluoride and get the connection of refractive with temperature and pressure under condition of Under-Critical, Near-Critical and Super-Critical through the way of dropping down pressure, but at the same time keep temperature constantly. Calculate and describe the track of laser beam through optical cell, and analysis the reason of of difference form of facular and the excursion distance.It is found that the refractive index on the critical point is infinite. More near it get to the critical point ,the larger the refractive index is. When away form the critical point the refractive index fall rapidly.It is shown, when in Under-Critical area the density of fluid is symmetrical, and ray spreads linear. When in Near-Critical area there has density grads, and deflection appears. On the Critical Point the density is fluctuation, and ray dispersed. Ray will spread linear again when the fluids is in Super-Critical area.