Photonic pressure measurements using absorption spectroscopy and Fabry-Pérot refractometry

Abstract

During this thesis three individual experimental setups were built and characterized with the goal to perform highly accurate pressure measurements in the vacuum region between (10e-3 and 10e5) Pa. Absorption spectroscopy was used to measure the line strengths of three electromagnetic transitions of the rotational-vibrational spectrum of carbon monoxide in the fundamental band around 4.6 µm, with the lowest measurement uncertainties to date. The results agree with the latest theoretically calculated line strengths within their measurement uncertainty. Based on these (and other) accurate strength measurements, the realized absorption spectroscopy can effectively be used as an optical pressure standard for partial pressure measurements in the range of (10e-3 to 10e2) Pa. In addition, an optical refractometer for pressure measurement was successfully set up at PTB for the first time. The unique feature of this system is the dichroic coating of the mirrors of the Fabry-Pérot resonator on which it is based. Since the measured refractivity of a gas is not only pressure-dependent, but also depends on the wavelength of the laser used, this unique system was also able to investigate the dispersion relation of the refractive index of the three gases: Helium, nitrogen and argon with low uncertainties. The optical refractometer allows for pressure measurements in the range from (1 to 10e5) Pa. The resonator materials used for optical refractometers are often times made of specialized glasses, of which their helium permeation property was investigated with the third experiment, an ultra-high vacuum compatible helium outgassing rate measurement setup.