High-Power Lensless THz Imaging of Hidden Objects

Abstract

The potential of pulsed THz radiation for time-of-flight imaging applications is well recognized. However, advances in this field are currently severely limited by the low average power of ultrafast THz sources. Typically, this results in impractically long acquisition times and a loss in resolution and contrast. These limitations make imaging of the objects in real-life scenarios impossible. Here, conclusively, the potential of state-of-the-art high-average power THz time-domain spectrometer (TDS), driven by a 100-W class, one-box ultrafast oscillator for imaging applications is shown by demonstrating lensless THz imaging in reflection mode of a dielectric sample with low reflectivity. Images obtained with our home-built 20-mW average power THz-TDS system show a significant contrast enhancement compared to a state-of-the-art commercial THz-TDS with less than 200 µW of average power. Our unique setup even allows us to obtain images of such an object with high-contrast hidden inside a medium-density fiberboard (MDF) box. This opens the door to THz time-of-flight imaging of concealed objects of unknown shape and orientation in various real-life scenarios which were so far impossible to realize. INDEX TERMS High-power terahertz radiation, lensless terahertz imaging, terahertz time-domain spectroscopy

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

“…In our previous work [11], [12], we have demonstrated the principle of 2D THz-TDS imaging using the radar backprojection technique. Here, a brief overview is given as the basis for the 3D imaging technique.…”

“…The height of the cylindrical synthetic aperture is given as h sa . Using this measurement scenario, the shape and size of the OUT in all three dimensions can be reconstructed, where the resolution along the z-axis corresponds to the resolution of a linear synthetic aperture according to (9) and the resolution along the x-and y-axis is calculated using (11) and (12), respectively. In Fig.…”

“…All of these drawbacks limit the applications of terahertz imaging in real-life scenarios. Thus, in [11] and [12] we proposed a terahertz time-domain spectroscopy (THz-TDS) based imaging approach using a divergent beam and a synthetic aperture for 2D imaging.…”

Fivefold Peak Power Boost in HBT-Driven GaAs Collapsing-Field-Domain-Based Sub-THz Source

“…Within the last few decades, time-domain spectroscopy (TDS) and time-domain imaging (TDI) have become accessible techniques via the implementation of femtosecond laser-driven pulsed sources [1]- [3]. Their recent applications include biophotonics [4], [5], security scanning [6], and other [7]. While the temporal resolution of such systems reaches hundreds of femtoseconds [8], [9], most TDI/TDS THz setups remain bulky, expensive, and energy-consuming, limiting their real-world applications.…”

Concurrent-Mode CMOS Detector IC for Sub-Terahertz Imaging System

“…Terahertz (THz) waves represent frequencies of the 0.1-10 THz bands of the frequency spectrum. Located between radio and light waves, THz waves with high transmittance and directivity are expected to be widely used in the fields of security imaging, radio astronomy, medical imaging, and art [1][2][3][4][5][6][7]. A THz imaging system is capable of nondestructive inspection owing to the low ionization energy with regard to frequency.…”