Fiber Optics for Terahertz Detection: Toward Single-Pulse Terahertz Detection Using the Dispersive Fourier Transform

Abstract

Terahertz spectroscopy shows promise in applications including quality control, security and medical imaging, but remains limited by slow data acquisition. This also poses an impediment to the study of samples undergoing irreversible transitions, as typical schemes rely on the assumption that results are consistent from pulse to pulse. In this work, we propose a high-speed terahertz detection technique based on chirped-pulse encoding that can enable single-shot measurements up to laser repetition rates in the MHz. An all-normal dispersion optical fiber is used to create a broadband probe spectrum, onto which the terahertz pulse waveform is encoded as a phase modulation. The sampling process makes use of the dispersive Fourier transform, a technique which maps the spectral features of a pulse into the time domain, in this case via the dispersion of a long commercial optical fiber. The elongated pulse can subsequently be detected with a high-speed photodetector and oscilloscope. We show steps toward implementing the technique by characterizing the components required to shape the probe pulse and providing some proof-of-concept measurements. In addition, fiber optic simulation procedures are detailed including complete coupled generalized nonlinear Schrödinger equations to provide insight into polarization effects that occur during highly nonlinear processes such as supercontinuum generation.