Design Of Optical Cell Of Supercritical Fluid And Measurement Of Refractive Indexes Of Supercritical Fluid

The density of SCFNCP(Super Critical Fluid Near Critical Point) changes sharply when its temperature and pressure changes, so the optical property such as the refractive index may changes sharply too. The main objective of this thesis is searching after the phenomena and the principles of the refractive indexes of SCFNCP primarily. The more important significance is finding a new way to compress the laser pulse duration and to adjust the laser frequency from the principles.The optical cell of supercritical fluid is designed according to the requirement of the experiment. Its compressing resistance is 16MPa. The way of establishing the pressure of the SCF(Super Critical Fluid) is as follows: The pressure testing hand pump compresses hydraulic oil into the accumulator, so the cubage of the capsule in the accumulator is getting small, the pressure of the fluid in the capsule rises. The pressurizing system with two stage is adopted according to the calculating result with the compression limit of the capsule and the pressure demanded in experiment. The way of establishing the condition of temperature of the SCF(Super Critical Fluid) is as follows: the temperature of the circulating water is controlled by aqueous thermostat, the circulating water is infused into water jacket of the optical cell, the heat is transferred to SCF by the wall of the optical cell, then the temperature of the SCF rises to the super critical temperature. The teflon gaskets is selected to seal the windows of the optical cell, and it is deformed a little at high pressure, so it won't block the laser beam.The method of measuring the refractive index by the Michelson interferometer is widely used with high precision, but the optical cell of supercritical fluid is too big to be put in the existing Michelson interferometer. There are many factors of affecting the measuring precision in the large Michelson interferometer equipment. The most difficult problems are adjusting the two reflectors to aplanatic state and make the track of the stepper motor parallel to the optical path.The refractive indexes of the carbon dioxide near critical point are measuring by the method of two projecting points in screen when the temperature are 22.5℃,27℃,30℃,32℃, 35℃,40℃and the pressure are 5MPa,6MPa,7MPa, 8MPa, 9 MPa,10MPa respectively. The states of carbon dioxide(such as the gas, the liquid ,vapor-liquid ,SCF, and so on) at each temperature and pressure and the phenomenon of the critical opalescence are observed, the shapes of the light spot(like dot, cometary, strip, flame and so on) are recorded. The phenomenon of the critical opalescence appears at different temperature and different pressure if the density of the carbon dioxide is different, so it is put forward that the critical point isn't determined only by the temperature and the pressure of the matter, but also the density. A important law developed from the experimental data is that nearer the critical point, larger the refractive index of CO2, naturally when the fluid is far from the critical point, its index is smaller. Another important law is that the refractive index of SCFNCP is not only the function of density, but the function of temperature and pressure, which is background by the fact that the refractive index of SCFNCP changes as the temperature and pressure varies at the same density.The optical cell of supercritical fluid and the methods of controlling the temperature and the pressure can be referenced for the similar experiments. The refractive indexes of carbon dioxide of SCFNCP measuring in the experiment provide the basic data for the investigation of optical properties of SCFNCP. The forms of the carbon dioxide near critical point observed and noted in the experiment are helpful to the researcher interested in the thermodynamic property of the SCF.