Terahertz time domain spectroscopy and imaging: Emerging techniques for food process monitoring and quality control

Gowen, Aoife; O'Sullivan, Créidhe M.; O’Donnell, Colm P.

doi:10.1016/j.tifs.2011.12.006

Cited by 198 publications

(108 citation statements)

References 36 publications

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“…Generation and detection of radiation across the far infrared or Terahertz (THz) region of the electromagnetic spectrum is promising for a large variety of strategic applications, 1 ranging from biomedical diagnostics 2 to process and quality control, 3 homeland security 1 and environmental monitoring. 4 Due to its non-ionizing nature, 1 THz radiation can penetrate many commonly used dielectrics, 1 otherwise opaque for visible and mid-infrared light, allowing detection of specific spectroscopic features 5 with a sub-millimeter diffractionlimited resolution.…”

Section: Introductionmentioning

confidence: 99%

High performance bilayer-graphene terahertz detectors

Spirito

Coquillat

Bonis

et al. 2014

Applied Physics Letters

169

132

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We report bilayer-graphene field effect transistors operating as THz broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity~1.2V/W (1.3 mA/W) and a noise equivalent power~2×10 -9 W/√Hz in the 0.29-0.38THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.Generation and detection of radiation across the far infrared or Terahertz (THz) region of the electromagnetic spectrum is promising for a large variety of strategic applications, 1 ranging from biomedical diagnostics 2 to process and quality control, 3 homeland security 1 and environmental monitoring. 4 Due to its non-ionizing nature, 1 THz radiation can penetrate many commonly used dielectrics, 1 otherwise opaque for visible and mid-infrared light, allowing detection of specific spectroscopic features 5 with a sub-millimeter diffractionlimited resolution. µV/W and operating in photovoltage mode at much higher frequencies (2.5 THz).Here we report THz detectors operating at RT in either photovoltage or photocurrent mode with a significant enhancement of sensitivity and lowered NEPs compared to the state of the art. This is achieved by using either large (1 µm) gate lengths, or buried gate geometries on a bilayer graphene (BLG) FET. We use BLG instead of single layer graphene (SLG) since the modulation of carrier density was proved to be more effective in the former case, 19 allowing a higher responsivity at THz frequencies.The devices are prepared as follows. Flakes are mechanically exfoliated from graphite 24 on an intrinsic Si substrate covered with 300nm SiO 2 . BLGs are selected and identified by a combination of optical microscopy 25 and Raman spectroscopy. 26,27 These are then used to fabricate two sets of FETs (samples A, B). In A, source (S) and drain (D) contacts are patterned by electron beam lithography (EBL) and metal evaporation (5nm Cr /80 nm Au). The S contact is connected to one lobe of a 50° bow-tie antenna, and D to a 3 metal pad. After placement of 35nm HfO 2 by atomic layer deposition (ALD), the other lobe of the antenna is fabricated, and constitutes the FET gate (g). The channel length is L SD = 2.5 m, while the gate length w G =1 m (Fig. 1a). In B, one lobe of a log-periodic circular-toothed antenna is fabricated by EBL and metal evaporation to act as buried gate. After deposition of 35 nm HfO 2 by ALD, S and D electrodes are fabricated.Similar to sample A, S is the second lobe of the antenna, while the drain is a metal line connecting to a bonding pad. The channel length is 2.5 m, its width 7.5 m, while w G = 0.3m (Fig. 1b). A BLG flake is then placed onto the pre-fabricated electrodes by wet transfer. 28 Fig. 2 compares the Raman spectra of the flake prior and after placement onto the electrodes. The "2D" peak shows the characteristic multi-band s...

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Section: Introductionmentioning

confidence: 99%

High performance bilayer-graphene terahertz detectors

Spirito

Coquillat

Bonis

et al. 2014

Applied Physics Letters

169

132

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“…Therefore, the pulsed imaging is widely employed in various commercial/research imaging systems for online or offline inspections. 10,11 However, there are some limitations of working with the THz-TDS system. 12 Specifically, the THz imaging based on TDS systems is limited due to the low optical power.…”

confidence: 99%

Terahertz imaging using photomixers based on quantum well photodetectors

Zhou

Wan

et al. 2017

AIP Advances

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Due to the fast intersubband transitions, the terahertz (THz) quantum well photodetector (QWP) is supposed to work fast. Recently it has been demonstrated that the THz QWP can detect the THz light modulated at 6.2 GHz and therefore it can be used as a photomixer [H. Li et al., Sci. Rep. 7, 3452 (2017)]. In this work, the authors report a novel active THz imaging using THz QWP photomixers. The THz radiation source used for this imaging application is a multi-mode THz quantum cascade laser (QCL) operating in continuous wave mode. When the fast THz QWP is illuminated by the multi-mode THz radiation, the intermediate frequency signal that is resulted from the frequency beating between the neighbouring THz modes of the QCL can be extracted from the QWP mesa for imaging applications. Employing the technique, the frequency can be down-converted from the THz range to the microwave regime. And therefore, the signal can then be amplified, filtered, and detected using the mature microwave technology.

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“…Source: [6] THz detectors are desirable since the electromagnetic radiation in this region have the ability to penetrate most non-metallic, non-polar materials, while also having the distinct advantage of being non-ionizing [6]. Due to these distinctive properties, the technology can be utilized for advanced personnel security screening, food inspection, and medical diagnostics, among many other uses [2,8,9]. The ability for nondestructive evaluation and inspection is evident over a wide range of materials that exhibit THz spectral characteristics, including human body tissue [3,10].…”

Section: Figure 1 Terahertz Radiation Within the Electromagnetic Spementioning

confidence: 99%

“…Recent developments in quantum cascade THz lasers and metamaterial-based THz absorbers allow design of compact imaging systems. These metamaterial-based sensor designs, which will be discussed in this thesis, have increased the potential applications in the THz region [8,10].…”

Section: Figure 1 Terahertz Radiation Within the Electromagnetic Spementioning

confidence: 99%

Metamaterial Resonant Absorbers for Terahertz Sensing

Stinson¹

2015

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington, DC 20503. AGENCY USE ONLY (Leave blank) REPORT DATEDecember 2015 REPORT TYPE AND DATES COVERED 12a. DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution is unlimited 12b. DISTRIBUTION CODE ABSTRACT (maximum 200 words)The aim of this work is to develop a metamaterial absorber that can be incorporated into a terahertz (THz) imaging system with a 4.7 THz quantum cascade laser (QCL) illumination source. Finite element (FE) simulations were utilized to design metamaterials, and a Fourier transform infrared spectrometer (FTIR) was employed to characterize the absorption spectrum of each metamaterial configuration. Process parameters for future work with the microfabrication devices have been established for the Naval Postgraduate School clean room. Analysis of experimental data provided insight in determining the refractive index of the metamaterial dielectric, SiO x , from 3-8 THz and confirmed the Lorentzian shape for the absorption spectrum as theoretically proposed by another group. Future work will incorporate the metamaterial absorber design of this research into a more efficient, cost effective, bi-material THz sensor that can be employed in a variety of naval applications. SUBJECT TERMS

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Terahertz time domain spectroscopy and imaging: Emerging techniques for food process monitoring and quality control

Cited by 198 publications

References 36 publications

High performance bilayer-graphene terahertz detectors

High performance bilayer-graphene terahertz detectors

Terahertz imaging using photomixers based on quantum well photodetectors

Metamaterial Resonant Absorbers for Terahertz Sensing

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