Realising a pressure standard by measuring the refractive index of a gas
The pressure standard is based on measuring the refractive index of a gas using a Michelson homodyne interferometer, in which the measuring branch consists of two quasi-parallel mirrors through which the optical path of the laser beam is multiplied.
The research aims to obtain a primary pressure standard in the range of 100 Pa to 150 kPa with a relative standard uncertainty of less than 10 ppm at atmospheric pressure.
The study is currently focused on the accurate measurement, in a vacuum, of the optical path difference between the two branches of the interferometer and the realisation of an active thermal control system.
Realising a density/pressure sample by measuring Rayleigh scattering
The experiment is based on a typical manifestation of radiation-matter interaction, Rayleigh scattering in the presence of gas molecules, in particular by exploiting the pressure dependence of the gas.
Recently, the system has been characterised in the pressure range between 15 kPa and 900 kPa. The relationship between the scattered light and gas pressure was found to be strongly linear (R2 > 0.9999), promising the possible future development of sensors based on this technique. Furthermore, an accurate determination of the efficiency of the photon collection system could allow an absolute measurement of the density/pressure of a gas.