Photons and magnons can interact by dipolar interactions and magneto-optic effects. These interactions are used for versatile magnon spectroscopy methods and are the foundation for the fields of cavity spintronics and opto-spintronics. Key challenges in these fields are the strong coupling of cavity photons and magnons and efficient up-conversion from GHz frequency magnetic excitations to the optical regime.
We exploit the interaction of optical photons and magnons for spectroscopy of Dzyaloshinskii-Moriya interaction  and develop novel magneto-optical techniques that combine spatial resolution with phase-sensitivity over a broad frequency range . We showed that the hybrid interaction of a coupled magnon-photon microwave systems can be tuned from weak to strong coupling  and up-converted to optical frequencies .
 H. T. Nembach, J. M. Shaw, M. Weiler, E. Jué, and T. J. Silva, Linear relation between Heisenberg exchange and interfacial Dzyaloshinskii-Moriya interaction in metal films, Nat. Phys. 11, 825 (2015).
 L. Liensberger, L. Flacke, D. Rogerson, M. Althammer, R. Gross, and M. Weiler, Spin-Wave Propagation in Metallic Co25Fe75 Films Determined by Microfocused Frequency-Resolved Magneto-Optic Kerr Effect, IEEE Mag. Lett. 10, 5503905 (2019).
 H. Maier-Flaig, M. Harder, S. Klingler, Z. Qiu, E. Saitoh, M. Weiler, S. Geprägs, R. Gross, S. T. B. Goennenwein, and H. Huebl, Tunable magnon-photon coupling in a compensating ferrimagnet—from weak to strong coupling, Appl. Phys. Lett. 110, 132401 (2017).
 S. Klingler, H. Maier-Flaig, R. Gross, C.-M. Hu, H. Huebl, S. T. B. Goennenwein, and M. Weiler, Combined Brillouin light scattering and microwave absorption study of magnon-photon coupling in a split-ring resonator/YIG film system, Appl. Phys. Lett. 109, 72402 (2016).