Broadband in-line terahertz 2D imaging: comparative study with time-of-flight, cross-correlation, and Fourier transform data processing

摘要

A pulsed broadband (from 0.1 to 1.5 THz), in-line, terahertz (THz) time domain electro-optical sampling is applied for the visualization of phase objects by using a large-aperture electro-optical crystal (ZnTe, 1 cm x 1 cm). The waveforms of the THz pulses are generated in a lithium niobate (LiNbO3) crystal pumped by femtosecond pulses with a tilted amplitude front, and measured by a 2D THz imaging system. This system images the object under study in the THz range via a polytetrafluoroethylene (PTFE) lens in the 2f - 2f geometry onto a ZnTe crystal and then images the crystal surface on a CMOScamera using electro-optical sampling. Reconstruction of the image in such a scheme is implemented by processing the received 3D spatial-temporal distributions of the THz field in three different ways: (i) by detecting the displacement of the maximum peak position of the THz pulse due to a phase delay in the object under study; (ii) by using a cross-correlation function analysis; and (iii) by a Fourier transformation of a THz waveform and subsequent extraction of the phase difference at each THz frequency. Images of transparent PTFE objects were obtained. Main features of the resulting imaging system are discussed. (C) 2018 Optical Society of America.