Principal Investigator Nuh Gedik
Terahertz Time-Domain Spectroscopy (THz-TDS) is an optical technique used to measure equilibrium and non-equilibrium far infrared material properties such as index of refraction and conductivity. A THz pulse is generated via optical rectification in a ZnTe crystal using a 100 fs near-infrared pulse. The THz pulse is then focused through a sample and subsequently detected in another ZnTe crystal via free space electro-optic detection. The measured signal is proportional to the electric field of the pulse, so the magnitude and phase are preserved, and the complex transmission coefficient can be extracted. From this, the full complex value of the material parameters can be extracted without the use of Kramers-Kronig relations.
This can also be done after excitation by another 100 fs near-infrared pulse. By varying the time delay between the THz pulse and the excitation pulse, the non-equilibrium complex material parameters can be measured as a function of time, with resolution < 500 fs.
THz-TDS is best used to study systems in which the excitations of interest lie in the meV energy range, e.g., a superconductor with a small energy gap. The technique has been used to study a wide variety of systems, including Cooper pair and vortex dynamics in superconductors, carrier dynamics in semiconductors, metal-insulator phase transitions, and even metamaterials.