Using orbital angular momentum beams in a Michelson interferometer opens the possibility for non-invasive measurements of refractive index changes down to 10 refractive index units. We demonstrate the application of a twisted light interferometer to directly measure the concentration of NaCl and glucose solutions label-free and in situ and to monitor temperature differences in the mK-µK range. From these measurements we can extract a correlation of the refractive index to concentration and to temperature from a liquid sample which is in good agreement with literature.
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