Coherent reconstruction of a textile and a hidden object with terahertz radiation

Abstract

Imaging through scattering materials is of utmost importance, especially for security and biomedical imaging. Unlike the rest of the electromagnetic spectrum, terahertz radiation is a non-ionizing probe and allows imaging deep through non-conducting materials with sub-millimeter resolution. Here, we propose a coherent imaging technique reconstructing two objects, hidden one behind the other, from relative shifts between them. Experimental reconstructions at λ 96.5 μm of amplitude and phase objects hidden behind a glass fabric sample are presented. The hidden objects are retrieved with a lateral resolution of ≈1.5λ and a depth resolution of ≈λ∕10. Besides envisioning its use in noninvasive imaging, we anticipate that, in selected applications, the suggested approach can replace a similar phase retrieval technique, namely ptychography.

Roadmap of Terahertz Imaging 2021

“…Moreover, it provides a possibility to reveal pattern of object thicknesses, density distribution and relief features. The employment of highly coherent THz sources allows for achieving high-fidelity amplitude and phase reconstructions, as well as indicates ways of how to reconstruct images of complex dielectric targets [258]. Recent activities are dedicated to increasing quality of THz holography and extending new areas of application in this rapidly evolving field of THz optics.…”

“…Apart from well-established THz tomography technique, intelligent ideas were taken from the optical range to cope with obstacles in different imaging scenarios. Recent achievements for multi-thin layers 3D scheme reconstruction witness this by the works of 'Shape-fromfocus for real-time terahertz 3D imaging' [264], 'Multi-layered full-field phase imaging using continuous-wave terahertz ptychography' [265], and 'Coherent reconstruction of a textile and a hidden object with terahertz radiation' [258]. All of the three methods were developed by using the cameras working at THz range to scan in space.…”

“…Current challenges and possible future trends: As a rule, in real implementation conditions, for instance, in security or medicine, THz imaging needs to be done through scattering materials. It implies a search of new imaging techniques to tackle these problems [258]. An imaging system using broadband illumination typically faces the challenge of slow time-domain pulse sampling.…”

THz coherent lensless imaging

“…Microbolometers have been intensively applied for long-wave infrared coherent imaging [81]. Interestingly, the microbolometers designed for the wavelength range 8-14 µm possess better sensitivities than THz microbolometers around 100 µm [82] and thus have become the cameras of choice for lensless imaging applications [35,36,[83][84][85][86][87]. Notice that, however, care should be taken because their pixels are venerable to dazzling or permanent damage caused by a low-power (several µW) laser focused on several pixels.…”

“…First, its content will complement the two latest reviews of THz imaging [12,13], mostly focusing on THz-TDS imaging, near-field imaging, tomography, and compressive sensing. Second, we have realized that the peculiar interaction of THz radiation with materials triggered the development of new THz coherent lensless imaging techniques, which can in turn be implemented at different wavelengths [35,36]. This review is therefore meant to build a bridge between the THz and imaging communities, both of which are expected to benefit from it.…”