Task 4.1 Realising the pressure scale using optical methods

Construction of the alternative pressure standard.

The alternative pressure standard being developed in this work packages is based on ultra-sensitivity optical measurements of the gas refractivity. From the measurements of the gas refractivity, the gas pressure can, through gas density, be calculated.

The measurements are based on the use of two lasers that is frequency-locked to a dual Fabry-Perot cavity. One cavity acts as the measurement cavity, while the other is the vaccum reference. By monitoring the difference in frequency between the two lasers, the difference in refractivity in the two cavities can be measured.

This work is performed at Umea University.

fig1

Fig 1.  The cavity made of Zerodur and the free-space optics installed on the optical table.

fig2

Fig 2. Part of the vacuum system used for the initial testing.

fig3

Fig 3. Overview of the system at the optical table

fig4

Fig 4. The Zerodur cavity is being lit-up in order to check the mirror alignment.