Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of refractive index and equation of state in dense He, H2,
  H2O, Ne under high pressure in a diamond-anvil cell   We present an accurate determination of the refractive index of hydrogen,
helium, H2O and neon up to 35 GPa at ambient temperature. The experimental
method is based on the combination of two interferometric signals of the
Fabry-Perot cavity containing the sample in the diamond anvil cell. The data
are put in perspective through the variation of the molecular polarisability
with density. Significant electronic changes are observed. Interesting
possibilities of the method are also illustrated: the high precision to finely
probe phase transition; the simultaneous measurement of the volume to obtain
the equation of state of transparent media with around 1 % accuracy.

27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys