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

Lorenzo Valzania, Peter Zolliker, and Erwin Hack

Fig. 1. Setup and summary of the implemented reconstruction technique. A collimated laser beam coming from the left impinges on a hidden object (here a Siemens star) and a cover object (here a schematic textile) at the distance 𝑢$u$ and with transmission functions 𝑜(𝐱)$o(\mathbf{x})$ and 𝑡(𝐱)$t(\mathbf{x})$, respectively. The intensity of the complex wavefield Ψ𝑗𝑘(𝐱)${\mathrm{\Psi }}_{jk}(\mathbf{x})$ is recorded with a camera at multiple distances 𝑣𝑘$v_k$ from the cover object. This stack of diffraction patterns allows reconstructing the complex wavefields exiting the cover object 𝜓𝑗(𝐱)${\psi }_j(\mathbf{x})$. By shifting the cover object by the amounts 𝐱𝑗${\mathbf{x}}_j$, the two transmission functions are retrieved.

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-6-4-518

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$\lambda =96.5\mathrm{\mu m}$ 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$\approx 1.5\lambda$ and a depth resolution of ≈𝜆/10$\approx \lambda /10$. Besides envisioning its use in non-invasive imaging, we anticipate that, in selected applications, the suggested approach can replace a similar phase retrieval technique, namely ptychography.

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