Calibration of terahertz sampling detectors for intense unipolar picosecond current pulses in waveguides

Terahertz pulses are nowadays commonly used in many areas of condensed matter physics to access material properties and explore transport phenomena at fast timescales. However, little work has been devoted to the full characterization of such pulses when confined in waveguides. In this work, we fabricate terahertz photoconductive switch detectors, located at various points along a coplanar waveguide, and sample the electrical pulses that pass by the detectors. Two different but consistent methods were developed to calibrate the pulse amplitude. Notably, we synchronize a commercial pulse generator with the laser in order to sample nanosecond-wide pulses with the photoswitch detectors, effectively turning the setup into an on-chip high-frequency sampling oscilloscope. Both methods give identical results on pulse current, voltage, and field amplitudes and enable an absolute characterization of the electrical pulse propagation along the waveguide. These techniques constitute a reliable tool to explore (non-linear) phenomena such as current or field induced magnetization switching or phase transitions, which take place at high THz intensities.

Automated summary

This work focuses on the full characterization of terahertz pulses confined in waveguides. Terahertz photoconductive switch detectors were fabricated and used to sample the electrical pulses. Two calibration methods were developed to accurately characterize the pulse amplitude. These techniques provide a reliable tool to explore nonlinear phenomena at high THz intensities.