Tobias Kampfrath

Multi-THz nonlinear optics and sub-cycle control of charge and spin

Strong THz electric and magnetic fields are harnessed to coherently control charge and spin in solids with sub-cycle resolution. Exploiting coherent THz phonons we transiently induce and destroy spin density wave order in pnictides.

Terahertz quantum optics with solid-state systems

Recent studies on ultrafast dynamics of solids and nanostructures using few-cycle electromagnetic transients in the far and mid infrared spectral regions are presented. We are able to excite with phase-locked wave forms reaching peak amplitudes beyond 1 V/Å which are comparable to inner-atomic fields. At the same time, a quantum-limited sensitivity is approached in electro-optic detection. Such capabilities are promising a completely new access to the quantum properties of both condensed matter and light.

Nonlinear terahertz spectroscopy of magnetically ordered solids

We report on two investigations demonstrating that terahertz spectroscopy is a powerful tool to study the orbital and spin dynamics of electrons in magnetically ordered solids. First, we show that the terahertz pulse emitted from a photo-excited ferromagnetic Fe film is highly sensitive to the motion of spin-polarized electrons along the film interfaces. Second, the magnetic field of an intense terahertz pulse is used to induce a transient magnetization in the antiferromagnet NiO via Zeeman coupling to the NiO spins. A long-lived spin precession at the magnon frequency of 1 THz results.