Spatial sampling of terahertz fields with sub-wavelength accuracy via probe-beam encoding

Jiapeng Zhao,Yiwen E,Robert W Boyd,Xi-Cheng Zhang,Kaia Williams

doi:10.1038/s41377-019-0166-6

Jiapeng Zhao, Yiwen E + Show 3 more

Open Access

https://doi.org/10.1038/s41377-019-0166-6

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Abstract

Recently, computational sampling methods have been implemented to spatially characterize terahertz (THz) fields. Previous methods usually rely on either specialized THz devices such as THz spatial light modulators or complicated systems requiring assistance from photon-excited free carriers with high-speed synchronization among multiple optical beams. Here, by spatially encoding an 800-nm near-infrared (NIR) probe beam through the use of an optical SLM, we demonstrate a simple sampling approach that can probe THz fields with a single-pixel camera. This design does not require any dedicated THz devices, semiconductors or nanofilms to modulate THz fields. Using computational algorithms, we successfully measure 128 × 128 field distributions with a 62-μm transverse spatial resolution, which is 15 times smaller than the central wavelength of the THz signal (940 μm). Benefitting from the non-invasive nature of THz radiation and sub-wavelength resolution of our system, this simple approach can be used in applications such as biomedical sensing, inspection of flaws in industrial products, and so on.

Highlights

The unique properties of terahertz (THz) radiation, such as its high transmittance through nonpolar materials and nonionizing photon energies, enable numerous novel possibilities in both fundamental research and industrial applications[1,2,3,4,5,6,7]
The object, a positive US Air Force (AF) target made with chromium, is wrapped in a 70-μm-thick piece of paper and placed immediately before the detection crystal
We have demonstrated that our near-field spatial sampling technique can provide sub-wavelength resolution with high-fidelity through the use of a spatially encoded probe, and have shown the possibility of improving this technique to achieve real-time THz imaging with both amplitude and spectral information[30,31]

Summary

Introduction

The unique properties of terahertz (THz) radiation, such as its high transmittance through nonpolar materials and nonionizing photon energies, enable numerous novel possibilities in both fundamental research and industrial applications[1,2,3,4,5,6,7]. The knowledge of the spatial profile of THz fields becomes very important. Due to the lack of efficient and economical THz cameras[8,9], characterizing the transverse structures of THz fields usually relies on raster scanning either the detector or the sample[10], resulting in a low signal-to-noise ratio (SNR) and slow speed when the number of pixels increases. Novel beam profiling approaches that involve computational sampling methods have emerged[11,12,13,14,15,16,17]. Computational sampling methods, which combine computational algorithms with optical imaging techniques, can improve the sampling speed and image quality, under weak illumination[18].

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