Prof. Manfred Fiebig（Department of Materials, ETH Zurich）
Nonlinear optics on ferroic materials
For a long time, the property of materials to show spontaneous long-rang ("ferroic") order was mostly associated to "magnetism", or rather "ferromagnetism". The contemporary search for novel multifunctional and so-called "smart" materials has been shifting the emphasis towards other forms of ferroic order. There are, however, few established techniques allowing us to study these new classes of materials. Here, nonlinear (i.e. wavelength-converting) optics is an outstanding tool that allows us to study the properties of ferroics. This versatility is based on the symmetry breaking accompanying each form of ferroic order. The symmetry breaking is readily detected by nonlinear optical processes like second harmonic generation (SHG). In particular, techniques like SHG benefit from the unique degrees of freedom of optical experiments, namely spatial resolution (visualization of domains and their manipulation) and time resolution (visualization of dynamical spin-charge-coupled processes down to the femtosecond range). My lecture will begin with an introduction to symmetry and a variety of classical crystal-optical phenomena. This will be the basis for the core part of the lecture in which I will discuss the characterization of ferroelectric, (anti)ferromagnetic and other forms of ferroic order and their interaction by nonlinear optics. I will devote special attention to the characterization of multiferroics by SHG.