3D Fourier imaging based on 2D heterodyne detection at THz frequencies

Yuan, Hui; Voß, Daniel; Lisauskas, Alvydas; Mundy, David; Roskos, Hartmut G.

doi:10.1063/1.5116553

Cited by 34 publications

(14 citation statements)

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“…THz Fourier imaging: Very recently, Fourier imaging recording the data in the Fourier domain folding the 3D information into 2D in the focal plane of the imaging system and reconstructing the 3D scenario by expanding the 2D data numerically was developed by Yuan etc. [262]. As delineated in Figure 5, the heterodyne detection at 300 GHz based on the nanometric FET-based sensor is utilized to capture the Fourier spectrum of the imaged target.…”

Section: Thz Computational Imagingmentioning

confidence: 99%

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Roadmap of Terahertz Imaging 2021

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Yuan

et al. 2021

Sensors

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In this roadmap article, we have focused on the most recent advances in terahertz (THz) imaging with particular attention paid to the optimization and miniaturization of the THz imaging systems. Such systems entail enhanced functionality, reduced power consumption, and increased convenience, thus being geared toward the implementation of THz imaging systems in real operational conditions. The article will touch upon the advanced solid-state-based THz imaging systems, including room temperature THz sensors and arrays, as well as their on-chip integration with diffractive THz optical components. We will cover the current-state of compact room temperature THz emission sources, both optolectronic and electrically driven; particular emphasis is attributed to the beam-forming role in THz imaging, THz holography and spatial filtering, THz nano-imaging, and computational imaging. A number of advanced THz techniques, such as light-field THz imaging, homodyne spectroscopy, and phase sensitive spectrometry, THz modulated continuous wave imaging, room temperature THz frequency combs, and passive THz imaging, as well as the use of artificial intelligence in THz data processing and optics development, will be reviewed. This roadmap presents a structured snapshot of current advances in THz imaging as of 2021 and provides an opinion on contemporary scientific and technological challenges in this field, as well as extrapolations of possible further evolution in THz imaging.

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Section: Thz Computational Imagingmentioning

confidence: 99%

“…Middle panels: Intensity (b) and phase images (c) for a reconstruction distance equal to the position of the washer; lower two panels: Reconstructed intensity (d) and phase (e), but for the distance equal to that of the screw. Figure modified from Ref [262]…”

mentioning

confidence: 99%

Roadmap of Terahertz Imaging 2021

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Lisauskas

Yuan

et al. 2021

Sensors

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193

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“…18,24,25 As such, they are being used for imaging applications with depth resolution 26 and for full-scale three-dimensional imaging. 27 The devices employed for this study (see Fig. 2, to be discussed below) were not specically designed for the task.…”

Section: Introductionmentioning

confidence: 99%

“… 18,24,25 As such, they are being used for imaging applications with depth resolution 26 and for full-scale three-dimensional imaging. 27 …”

Section: Introductionmentioning

confidence: 99%

Antenna-coupled field-effect transistors as detectors for terahertz near-field microscopy

et al. 2021

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“…key role in their development. Some impressive benchmarks are the successful implementation of a heterodyne scheme (which is important for s-SNOM as well) [158] and the measurement of human body radiation [159].…”

Section: Field-effect Transistors For Thz S-snommentioning

confidence: 99%

Optimization of the s-SNOM near-field nanoscopy for the investigation of transport phenomena on the nanometer length scale

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Classical light microscopy is one of the main tools for science to study small things. Microscopes and their technology and optics have been developed and improved over centuries, however their resolution is ultimately restricted physically by the diffraction of light based on its wave nature described by Maxwell’s equations. Hence, the nanoworld – often characterized by sub-100-nm structural sizes – is not accessible with classical far-field optics (apart from special x-ray laser concepts) since its lateral resolution scales with the wavelength. It was not until the 20th century that various technologies emerged to circumvent the diffraction limit, including so-called near-field microscopy. Although conceptually based on Maxwell’s long known equations, it took a long time for the scientific community to recognize its powerful opportunities and the first embodiments of near-field microscopes were developed. One representative of them is the scattering-type Scanning Near-field Optical Microscope (s-SNOM). It is a Scanning Probe Microscope (SPM) that enables imaging and spectroscopy at visible light frequencies down to even radio waves with a sub-100-nm resolution regardless of the wavelength used. This work also reflects this wide spectral range as it contains applications from near-infrared light down to deep THz/GHz radiation1. This thesis is subdivided into two parts. First, new experimental capabilities for the s-SNOM are demonstrated and evaluated in a more technical manner. Second, among other things, these capabilities are used to study various transport phenomena in solids, as already indicated in the title. On the technical side, preliminary studies on the suitability of the qPlus sensor – a novel scanning probe technology – for near-field microscopy are presented. The scanning head incorporating the qPlus sensor –named TRIBUS – is originally intended and built for ultra-high vacuum, low temperature, and high resolution applications. These are desirable environments and properties for sensitive nearfield measurements as well. However, since its design was not planned for near-field measurements, several special technical and optical aspects have to be taken into account, among others the scanning tip design and a spring suspended measurement head. In addition, in this thesis field-effect transistors are used as THz detectors in an s-SNOM for the first time. Although THz s-SNOM is already an emerging technology, it still suffers from the requirements of sophisticated and specialized infrastructure on both the detector and laser side. Field-effect transistors offer an alternative that is flexible, cost-efficient, room-temperature operating, and easy to handle. Here, their suitability for s-SNOM measurements, which in general require very sensitive and fast detectors, is evaluated. In the scientific part of this thesis, electromagnetic surface waves on silver nanowires and the conductivity/charge carrier density in silicon are investigated. Both are completely different concepts of transport phenomena, but this already shows the general versatility of the s-SNOM as it can enter both fields. Silver nanowires are analysed by means of near-infrared radiation. Their plasmonic behaviour in this spectral region is studied complementing other simulations and studies in literature performed on them using for example far-field optics. Furthermore, the surface wave imaging ability of the s-SNOM in the near-infrared regime is thoroughly investigated in this thesis. Mapping surface waves in the mid-infrared regime is widespread in the community, however for much smaller wavelengths there are several important aspects to be considered additionally, such as the smaller focal spot size. After that, doped and photo-excited silicon substrates are investigated. As the characteristic frequencies of charge carriers in semiconductors – described by the plasma frequency and the Drude model – are within the THz range, the THz s- SNOM is very well suited to probe their behaviour and to reveal contrasts, which has already been shown qualitatively by numerous literature reports. Here, the photo-excitation enables to set and tune the charge carrier density continuously. Furthermore, the analysis of all silicon samples focuses on a quantitative extraction of the charge carrier densities and doping levels ...

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3D Fourier imaging based on 2D heterodyne detection at THz frequencies

Cited by 34 publications

References 34 publications

Roadmap of Terahertz Imaging 2021

Roadmap of Terahertz Imaging 2021

Antenna-coupled field-effect transistors as detectors for terahertz near-field microscopy

Optimization of the s-SNOM near-field nanoscopy for the investigation of transport phenomena on the nanometer length scale

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