Terahertz Two-Dimensional Coherent Spectroscopy

The information provided by nonlinear THz spectroscopy is particularly useful as one can probe properties of materials that may be otherwise invisible to linear response conductivity. To study the nonlinear response in a 2DCS/pump-probe experiment, intense THz pulses were generated in a pair of LiNbO3 crystals using an amplified 800 nm Titanium:sapphire laser with ~3 mJ incident on each crystal in the tilted-pulse-front scheme. Using a two-pulse measurement scheme (EA and EB) with a differential chopping arrangement the response is measured from EA and EB individually and when both are incident on the sample EAB. The resulting nonlinear response due to both pulses is then obtained via ENL = EAB - EA - EB. The transmitted THz pulses were detected with standard electro-optic methods using ZnTe (for the single-pulse transmission experiments) or GaP (for all other two-pulse measurements) detection crystals. More details on the setup can be found in our papers.

We are using this technique to study quantum spin-liquids, electron glasses, magnets of various kinds, and interacting metals.