Rotational Raman scattering as a source of polarized radiation for the calibration of polarization-based Thomson scattering

We discuss the use of rotational Raman scattering as a possible technique for the calibration of polarization based plasma diagnostics such as the polarimetric Thomson scattering (TS) systems proposed for the measurement of electron density ne and temperature Te in very hot fusion plasmas. First by using the Stokes vector formalism, we calculate the Mueller matrix of rotational Raman scattering from a diatomic gas (such as H2, D2 and N2) for a generic scattering angle and then we use it to describe in detail the polarization characteristics of the Raman radiation available in the typical conditions of a TS system in a fusion plasma. Then we consider the various experimental set-ups proposed for polarimetric TS and show that rotational Raman scattering can generate radiation with known intensity and polarization states that, although not equal to those of the TS radiation, are suitable for the calibration of polarimetric TS diagnostics. Finally we point out that in fusion experiments Raman polarimetry may be of interest also for the calibration of other polarization-based measurement systems, such as the motional Stark effect (MSE) diagnostics.