Time-resolved THz spectroscopy experiments allow one to measure low energy excitations in materials on sub-picosecond time scales following optical perturbation. Depending on the material, one can probe the conductivity of mobile carriers, orbital transitions of excitons, infrared active phonons, and energy gaps that arise from many-body correlations (e.g. superconductivity). Our lab has several time-resolved systems: an all air-plasma THz spectrometer with sub-50 fs, sub-meV resolution, a high-field THz spectrometer for strongly perturbing charge and spin degrees of freedom coherently, and a novel THz pump - fs polarimetry setup designed to sense ultrafast asymmetry arising from charge/spin - lattice couping.
Advanced control over the flow of light is typically achieved by spatial patterning of a dielectric medium on sub-wavelength length scales. Such patterning controls the photonic band structure for light. We have devised a method to “write” virtually any two-dimensional photonic struture for THz frequency light using femtosecond optical pulses. This allows us to control the dielectric environment in both space and time and offers many interesting possiblities from capturing photons to optical black hole analogues.
In typical high vacuum systems, it takes roughly one second for a material to be completely covered in a monolayer of water. This is a major problem to experiments searching for exotic states of matter in 2D systems, since they are all surface! In collaboration with the Grutter group, we are investiging ultrafast carrier dynamics in 2D materials in an ultra-clean environment. For this we use a custom designed, ultra-high vacuum suitcase equipped with diamond windows for complete spectral coverage from visible to THz frequencies and a mass spectrometer for rest gas analysis.
The intense THz pulses we create in the lab have peak fields that approaching MV/cm. Shining them on a metal nanotip enhances this field via a lightning rod effect by a roughly a factor of 1000! At these fields, electrons are pulled directly from the metal and are accelerated to keV energies in < 10 fs. We are exploring the potential uses of such femtosecond electron bursts in our lab.