Measurement of the group velocity of light in sea water at the ANTARES site

The group velocity of light has been measured at eight different wavelengths between 385 nm and 532 nm in the Mediterranean Sea at a depth of about 2.2 km with the ANTARES optical beacon systems. A parametrisation of the dependence of the refractive index on wavelength based on the salinity, pressure and temperature of the sea water at the ANTARES site is in good agreement with these measurements.

► Group velocity of light measured by the ANTARES neutrino telescope in sea water.
► LEDs emit short duration flashes of different wavelengths detected by PMTs.
► Measurements show decrease of the refraction index with increasing wavelength.
► Measurements are in agreement with theoretical predictions.