Focus and Alignment Tolerance in a Photoconductive Terahertz Source

Abstract

Robust coupling between a pulsed laser beam and a photoelectric circuit is an important issue in the development of miniaturized, integrated, and embedded terahertz instrumentation. Here, we present a study of the effect of varying the focus and alignment parameters of an excitation laser pulse on the emission characteristics of a standard Hertziandipole type terahertz photoelectric source. The objective is to quantify the tolerance of a terahertz time-domain spectroscopy system, and we study the variation of peak amplitude, waveform, phase, and energy distribution as a function of excitation position and defocus. We find that a terahertz source can be made relatively tolerant to variations in focus, alignment, and details of the geometry of the photoelectric system, providing a window for a more robust field operation.

Fabrication and Characterization of an 8 × 8 Terahertz Photoconductive Antenna Array for Spatially Resolved Time Domain Spectroscopy and Imaging Applications

“…Due to the difference in the lifetimes and mobilities of electrons and holes, the detection at the electrode that is connected to the positive terminal of the transimpedance amplifier will be predominant. This phenomenon is known for PCA emitters where the THz power is maximal when the laser beam is focused close to the anode [51]- [55].…”