Terahertz homodyne spectroscopic imaging of concealed low-absorbing objects

Jokubauskis, Domas; Minkevičius, Linas; Seliuta, D.; Kašalynas, Irmantas; Valušis, Gintaras

doi:10.1117/1.oe.58.2.023104

Cited by 17 publications

(9 citation statements)

References 10 publications

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“…The so-called bow-tie diodes operating on non-uniform carrier heating effects demonstrate broader operational bandwidth reaching 2.5 THz for all investigated materials GaAs [175], GaAs/AlGaAs [176], and InGaAs [177], with the highest and nearly independent of frequency sensitivity of about 10 V/W below 1 THz for InGaAs sensors. They were found to be well-suited for multispectral THz imaging aims [178,179], and, together with their reliability and fast response times below 7 ns [180], can be implemented in real imaging systems to discriminate even weakly absorbing objects when tuned to heterodyne [181] or homodyne [182] operational modes. Recent technological innovation making use of new growth conditions [183] enabled increase of the sensitivity of 13 V/W and reduction of the NEP below 1 nW/ √ Hz at 0.6 THz due to strong built-in electric field effects.…”

Section: Thz Diodes-based Sensing and Microbolometers In Thz Imagingmentioning

confidence: 99%

Roadmap of Terahertz Imaging 2021

Valušis

Lisauskas

Yuan

et al. 2021

Sensors

175

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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 Diodes-based Sensing and Microbolometers In Thz Imagingmentioning

confidence: 99%

Roadmap of Terahertz Imaging 2021

Valušis

Lisauskas

Yuan

et al. 2021

Sensors

175

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show abstract

“…Therefore, a novel optical solutions [15] are needed allowing to design and manufacture compact optical elements with large aperture sizes and reasonable focal lengths. A special role can be attributed to the case of low absorbing or transparent samples, when the object observation and registration of its internal structure grow into a tremendous challenge [29]. It is related to the fact that power detectors record intensity of the radiation which suffers almost no observable change in the given circumstances, and the shift of the phase of incident radiation becomes a single quantity to be recorded.…”

Section: Imaging With Spatial Filtering Methodsmentioning

confidence: 99%

Titanium-Based Microbolometers: Control of Spatial Profile of Terahertz Emission in Weak Power Sources

Minkevičius

Siemion

et al. 2020

Applied Sciences

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Terahertz (THz) imaging and spectroscopy set-ups require fine optical alignment or precise control of spatial mode profile. We demonstrate universal, convenient and easy-to-use imaging—resonant and broadband antenna coupled ultrasensitive titanium-based—dedicated to accurately adjust and control spatial mode profiles without additional focusing optical components of weak power THz sources. Versatile operation of the devices is shown using different kinds of THz—electronic multiplier sources, optical THz mixer-based frequency domain and femtosecond optoelectronic THz time-domain spectrometers as well as optically pumped molecular THz laser. Features of the microbolometers within 0.15–0.6 THz range are exposed and discussed, their ability to detect spatial mode profiles beyond the antennas resonances, up to 2.52 THz, are explored. Polarization-sensitive mode control possibilities are examined in details. The suitability of the resonant antenna-coupled microbolometers to resolve low-absorbing objects at 0.3 THz is revealed via direct, dark field and phase contrast imaging techniques as well.

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“…In this case, only the power of THz radiation is detected, which restricts possible applications of the system and decreases the informational value of the obtained THz images, since lots of tiny details, particularly in the case of low-absorbing objects, are not recorded. More promising approaches to THz imaging are interferometric homodyne [8] or heterodyne [9] techniques, which allow one to increase the sensitivity of the system by orders of magnitude and to extract phase information as well. However, these approaches require more elaborate experimental equipment resulting in a higher sensitivity to optical alignment, which is not always possible to achieve, as well as significantly increased economic costs.…”

Section: Introductionmentioning

confidence: 99%

“…However, these approaches require more elaborate experimental equipment resulting in a higher sensitivity to optical alignment, which is not always possible to achieve, as well as significantly increased economic costs. Thus, there is a need to find rational trade-off between the cost and overall complexity of the THz imaging setup, on the one hand, and the quality of resulting images, on the other one [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Improvement of terahertz images by adaptive discrete cosine transform (DCT)-based denoising

Abramova¹,

Abramov²,

Grigelionis³

et al. 2022

physics

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Due to certain hardware limitations the quality of terahertz images is often lower than desired, which makes it difficult to extract valuable information from them. The goal of this paper is to investigate possibilities to overcome some of these limitations by means of digital image processing. The research is held on a set of images obtained at different distances from the source of terahertz radiation at 0.1 THz frequency. It is shown that the noise in these images is mixed and has a significant level of spatial correlation. For image quality enhancement a fully automatic denoising method based on the use of a discrete cosine transform with a spatially adapted spectrum is proposed. It is shown that despite an initially low spatial resolution of terahertz images and intensive noise, it provides a good noise reduction with a good preservation of edges, which allows one to noticeably improve the quality of these images and make them more convenient for visual analysis carried out by a human operator.

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Terahertz homodyne spectroscopic imaging of concealed low-absorbing objects

Cited by 17 publications

References 10 publications

Roadmap of Terahertz Imaging 2021

Roadmap of Terahertz Imaging 2021

Titanium-Based Microbolometers: Control of Spatial Profile of Terahertz Emission in Weak Power Sources

Improvement of terahertz images by adaptive discrete cosine transform (DCT)-based denoising

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