Because of the speed of light compared to material motion, the dragging of light is difficult to observe under laboratory conditions. Here, we report on the first observation of image rotation, i.e., a dragging by the medium of the wave’s transverse structure, of Alfvén waves in plasmas. Exploiting the naturally slow group velocity of these waves, significant wave rotation is achieved for modest angular frequency. Control over the rotation of the wave’s structure is demonstrated through the plasma rotation imposed by biased electrodes. Remarkably, experimental results are well reproduced by light dragging theory derived for isotropic media, even if magnetized plasmas are anisotropic. In addition to offering new insights into the fundamental issue of angular momentum coupling between waves and media, these findings also open possibilities for new remote rotation sensing tools.

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• Alfvén waves
• Angular momentum of light
• Light propagation, transmission & absorption
• Mechanical effects of light on material media
• Plasma waves