Department of Physical Chemistry, Fritz Haber Institute of the MPG 

Lattice Dynamics Group

Alex Paarmann
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Our group is interested in optical phonons in polar dielectric crystals and their heterostructures. We use various linear and nonlinear mid-infrared to THz spectroscopy techniques, employing the Infrared Free Electron Laser (IR-FEL) at the FHI as an intense and tunable light source.

Using this unique laser, we study phase transitions in complex materials, for instance correlated oxides, by means of the nonlinear-optical response enhanced at optical phonon resonances. Additionally, we develop new platforms for infrared-to-THz nanophotonics based on surface phonon polaritons, supported in sub-diffractional nanostructures and excited via prism coupling. We also currently develop an experimental end station for FEL-based surface-specific vibrational sum-frequency generation which will, for instance, allow us to study transient species in surface chemistry.