THz spectroscopy

Terahertz time-domain spectroscopy

The terahertz pulses can be generated and detected in nonlinear crystals or photoconductive antennas using femtosecond laser pulses. By scanning the time delay between generation and detection laser pulses, both the amplitude and phase of the THz electric field are recorded in the time domain. Then, the THz spectrum is obtained by Fourier transform. In either reflection and transmission measurement, the complex dielectric constant in terahertz ranges can be calculated based on a Fabry-Perot model.

Laser machined THz metasurface

We can fabricate micron-size features using laser machining.

Terahertz imaging

By mechanical scanning the sample, a spectral image can be obtained.

Pump-probe spectroscopy

A strong (optical or terahertz) pump pulse is used to excite the sample into a non-equilibrium state. Then, a weak (optical or teraherz) probe pulse is used to monitor the pump-induced change in material parameters. By scanning the delay of the pump and probe pulses, the relaxation dynamics of the sample can be studied.

Single-shot spectroscopy

Conventionally, recording a terahertz waveform or a pump-probe trace requires repetitively moving a translation stage to tune the delay. The data acquisition time is long and we cannot study irreversible processes like phase transitions or photochemistry. To address these issues, we have developed the single-shot detection technique. We can obtain a pump-probe trace or a terahertz spectrum with one laser shot.