Measurement of the Casimir force in a gas and in a liquid
We present here detailed measurements of the Casimir-Lifshitz force between two gold surfaces, performed for the first time in both gas (nitrogen) and liquid (ethanol) enviroments with the same apparatus and on the same spot of the sample. Furthermore, we study the role of double-layer forces in the liquid, and we show that these electrostatic effects are important. The later contributions were precisely subtracted to recover the genuine Casimir force, and the experimental results are compared with calculations using Lifshitz theory. Our measurements demonstrate that a carefull account of the actual optical properties of the surfaces is necessary for an accurate comparison with the Lifshitz theory predictions at short separations of less than ${200}\si{\nano\meter}