Bessel terahertz imaging with enhanced contrast realized by silicon multi-phase diffractive optics

Minkevičius, Linas; Jokubauskis, Domas; Kašalynas, Irmantas; Orlov, Sergej; Urbas, Antanas; Valušis, Gintaras

doi:10.1364/oe.27.036358

Cited by 34 publications

(35 citation statements)

References 30 publications

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“…To reduce the losses, high-density polyethylene (HDPE) materials or polyamide layers can be replace by high-resistivity silicon-based multilevel phase Fresnel lenses [211] or zone plates (Figure 4) fabricated, for instance, by laser ablation technology [212]. It was shown that such components can successfully be used for THz beam focusing, as well as beam-engineering, for instance, in Bessel or Fibonacci-beam generation [213,214]. The approach works well even for large apertures, up to 50 mm [215], and it allows for reaching nearly 90% transmittance of silicon antireflection layers and produce focusing by binary zone plates [216].…”

Section: Diffractive Optical Components and Beamforming (Beam Engineering) In Thz Imagingmentioning

confidence: 99%

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Roadmap of Terahertz Imaging 2021

Valušis

Lisauskas

Yuan

et al. 2021

Sensors

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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: Diffractive Optical Components and Beamforming (Beam Engineering) In Thz Imagingmentioning

confidence: 99%

“…Photo of high-resistivity silicon-based Bessel zone plate placed in the optical mount.The diffractive optical element is prepared by the laser ablation technology. More details on fabrication technology and the zone plate design can be found in Ref [213]…”

mentioning

confidence: 99%

Roadmap of Terahertz Imaging 2021

Valušis

Lisauskas

Yuan

et al. 2021

Sensors

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175

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“…This circumstance becomes of a particular importance in real-time inspection and sensing when a high capture rate of images is required, and detectors arrays need to be implemented in the recording set-up using collimated beams. Moreover, even in the case of bulky objects imaging, when extended focus [ 17 ] or bifocal (Fibonacci) focusing [ 18 ] helps to discriminate the content, control and monitoring of the beam shape along its propagation axis demands of special attention.…”

Section: Introductionmentioning

confidence: 99%

Antenna-Coupled Titanium Microbolometers: Application for Precise Control of Radiation Patterns in Terahertz Time-Domain Systems

Minkevičius

Urbanowicz

et al. 2021

Sensors

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An ability of lensless titanium-based antenna coupled microbolometers (Ti-μbolometers) operating at room temperature to monitor precisely radiation patterns in terahertz time-domain spectroscopy (THz-TDS) systems are demonstrated. To provide comprehensive picture, two different THz-TDS systems and Ti-μbolometers coupled with three different antennas—narrowband dipole antennas for 0.3 THz, 0.7 THz and a log-periodic antenna for wideband detection—were selected for experiments. Radiation patterns, spatial beam profiles and explicit beam evolution along the propagation axis are investigated; polarization-sensitive properties under various THz emitter power ranges are revealed. It was found that the studied Ti-μbolometers are convenient lensless sensors suitable to discriminate and control THz radiation pattern features in various wideband THz-TDS systems.

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“…The THz power was low in this system and the dark-field imaging resulted in the loss of most of the energy, which yielded a low signal to noise ratio (SNR) of the THz images. To improve the image contrast, Linas et al proposed the Bessel zone plate design based on silicon multi-phase diffractive optics, which was demonstrated in continuous wave mode at 0.6 THz [35]. Despite significant experimental and theoretical progress in this area, SSF imaging at the THz band is still not satisfactory.…”

Section: Introductionmentioning

confidence: 99%

Terahertz Spiral Spatial Filtering Imaging

Liu

Zhao

et al. 2021

Applied Sciences

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In this paper, we propose a terahertz (THz) spiral spatial filtering (SSF) imaging method that can enable image contrast enhancement. The related theory includes three main steps: (1) the THz image of the target is Fourier transformed to the spatial spectrum distribution; (2) the spatial spectrum is modulated by a spiral phase at the Fourier plane; (3) the filtered spatial spectrum is inverse Fourier transformed to the desired THz image. Meanwhile, analytic expression of the final THz image is derived. Due to the unique nature of the spiral phase, THz image contrast enhancement can be achieved and verified by various simulated target images with different contrasts. In our designed THz SSF imaging system, Fourier transform is carried out by the lens, and the spiral phase is acquired by the spiral phase plate (SPP). Proof-of-principle experiments with three different types of targets (carved metal letters, a high-density polyethylene (HDPE) piece with a scratch, and a leaf) were carried out, and the effectiveness of contrast enhancement and edge extraction on the THz reconstruction images was validated.

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Bessel terahertz imaging with enhanced contrast realized by silicon multi-phase diffractive optics

Cited by 34 publications

References 30 publications

Roadmap of Terahertz Imaging 2021

Roadmap of Terahertz Imaging 2021

Antenna-Coupled Titanium Microbolometers: Application for Precise Control of Radiation Patterns in Terahertz Time-Domain Systems

Terahertz Spiral Spatial Filtering Imaging

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