Ultrafast terahertz spectroscopy: from spin-dependent electron transport to single-cycle nonlinear optics
Prof. Dr. Dmitry Turchinovich (Max Planck Institute for Polymer Research)

Many elementary physical processes in condensed matter, such as electron momentum scattering, spin precession, molecular or lattice vibration etc belong to the terahertz (THz) frequency range [typically 0.2-20 THz, corresponding to photon energy 1-80 meV, wavelength 1.5 mm-15 μm, or wavenumbers 6-660 cm-1]. Ultrafast THz spectroscopy is based on the generation and field-resolved detection of single-cycle, sub-picosecond pulses of THz radiation, and combines two intertwined dimensions: materials science and photonics. The relevant spectral range and ultrafast time resolution allows for spectroscopy of interesting materials systems directly on the timescales, where many elementary physical phenomena occur. For example, ultrafast electron transport and scattering in graphene, or excitation and control of spin waves in canted antiferromagnets can be studied. The ability to “look inside an optical cycle” of the THz waveform during a light-matter interaction event enables the direct observation of interesting optical effects. For example, the self-phase modulation of a single-cycle pulse of light can be directly observed in the time domain, with sub-cycle time resolution.
After a brief discussion of basic principles of ultrafast THz spectroscopy, we will consider several recent case studies performed in ultrafast dynamics and terahertz spectroscopy group at MPIP. These cases include:
 contact-free ultrafast conductivity measurements in semiconductors and graphene  nonlinear electron transport in strong THz fields, and single-cycle nonlinear optics  excitation and coherent control of THz spin waves, and giant magneto-resistance observed in the THz range  ultrafast switching with THz signals, and possible applications in terabit electronics  ultrabroadband spectroscopy of vibrational modes in polymers