Intense terahertz generation from photoconductive antennas

In this paper,we review the past and recent works on generating intense terahertz(THz)pulses from photoconductive antennas(PCAs).We will focus on two types of large-aperture photoconductive antenna(LAPCA)that can generate high-intensity THz pulses(a)those with large-aperture dipoles and(b)those with interdigitated electrodes.We will first describe the principles of THz generation from PCAs.The critical parameters for improving the peak intensity of THz radiation from LAPCAs are summarized.We will then describe the saturation and limitation process of LAPCAs along with the advantages and disadvantages of working with widebandgap semiconductor substrates.Then,we will explain the evolution of LAPCA with interdigitated electrodes,which allows one to reduce the photoconductive gap size,and thus obtain higher bias fields while applying lower voltages.We will also describe recent achievements in intense THz pulses generated by interdigitated LAPCAs based on wide-bandgap semiconductors driven by ampli-fied lasers.Finally,we will discuss the future perspectives of THz pulse generation using LAPCAs.

Printing accuracy tracking with 2D optical microscopy and super-resolution metamaterial-assisted 1D terahertz spectroscopy

Printable electronics is a promising manufacturing technology for the potential production of low-cost flexible electronic devices,ranging from displays to active wear.It is known that rapid printing of conductive ink on a flexible substrate is vulnerable to several sources of variation during the manufacturing process.However,this process is still not being subjected to a quality control method that is both non-invasive and in situ.To address this issue,we propose controlling the printing accuracy by monitoring the spatial distribution of the deposited ink using terahertz(THz)waves.The parameters studied are the printing speed of an industrial roll-to-roll press with flexography printing units and the pre-calibration compression,or expansion factor,for a pattern printed on a flexible plastic substrate.The pattern,which is carefully selected,has Babinet’s electromagnetic transmission properties in the THz frequency range.To validate our choice,we quantified the geometric variations of the printed pattern by visible microscopy and compared its accuracy using one-dimensional THz spectroscopy.Our study shows a remarkable agreement between visible microscopic observation of the printing performance and the signature of the THz transmission.Notably,under specific conditions,one-dimensional(1D)THz information from a resonant pattern can be more accurate than two-dimensional(2D)microscopy information.This result paves the way for a simple strategy for non-invasive and contactless in situ monitoring of printable electronics production.