Speaker
Description
Terahertz time-domain spectroscopy (THz-TDS) has been established as a powerful tool for both industrial material inspection and fundamental material science. The latter strongly benefits from measuring conductivities, dielectric functions, and related phase transitions in e.g. semiconductors, topological insulators, high-temperature super-conductors, and 2D materials. Moreover, THz-TDS is well suited to investigate ultrafast, and thus non-equilibrium, quasi-particle dynamics in such solid-state systems. Its field-resolved detection allows for the measurement of both amplitude and phase of the light’s electric field and thus directly provides complex-valued static and transient material properties.
Here, we extend this technique to measure additionally the temporal evolution of the field’s polarization state for direct determination of complex tensorial materials responses. We advance this time-domain ellipsometry, previously mainly demonstrated in the low-THz spectral region (0.1 – 10 THz), towards the mid-Infrared (MIR, 15 – 40 THz) via OPA-based difference frequency generation and by implementing rapid two-dimensional electro-optic sampling (2D-EOS). With this method, we enable anisotropic transmittivity or reflectivity studies in a spectral region where fundamental resonances such as phonons, molecular vibrations, excitonic transitions, or cooper pairs can be found. As a benchmark system, we study the MIR birefringence of y-cut α-quartz. We directly extract the complex-valued dielectric tensor components in the vicinity of the anisotropic 21 THz (90 meV) and 24 THz (100 meV) phonon resonances. To verify our method, we fit a Lorentz oscillator model to our data and compare our results to free-electron-laser-based studies by Winta et al. from the Paarmann group [1]. The good agreement of these results shows that we developed a versatile table-top time-domain ellipsometer that will be used to also measure non-equilibrium tensorial properties in the near future. Currently, we are working towards circularly polarized pulses to trace transient circular dichroism and achieve chiral selectivity in the MIR.
References
[1] C.J. Winta et al., Phys. Rev. B 99, 144308 (2019).
| Abstract Number (department-wise) | PC 09 |
|---|---|
| Department | PC (Wolf) |
