Holographic measurement of high viscosities

We describe a holographic method for measuring very high viscosities, up to 10¹⁵ poise, or higher. The method consists of detecting small displacements, due to the sample deformation, by the holographic double exposure technique. Measurements performed on amorphous selenium are reported and compared with those obtained with the usual technique, showing that our method gives the correct results. The advantages of the proposed technique are briefly discussed.