# Is it possible to measure pressure in a vacuum using light?

I was wondering if it possible to measure the pressure in a vacuum using light.

$$n-1 = Ap$$
for some constant $A$. After calibration, measuring the refractive index of the gas using geometric methods should give you the pressure.
• And interferometric experiments can give you very high precision in measuring $n$. But there are some hitches. First, interferometry makes it easy to measure change in $n$, but you need an absolute reference to measure the value of $n$. And second the right reference is a complete vaccuum which is, well, hard to obtain. – dmckee Jul 14 '17 at 16:49