Terahertz confocal microscopy with a quantum cascade laser source

Cumis, Ugo Siciliani de; Xu, J.; Masini, Luca; Degl’Innocenti, Riccardo; Pingue, Pasqualantonio; Beltram, Fabio; Tredicucci, Alessandro; Vitiello, Miriam S.; Benedetti, Pier Alberto; Beere, Harvey E.; Ritchie, D. A.

doi:10.1364/oe.20.021924

Cited by 44 publications

(17 citation statements)

References 20 publications

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“…Since these waveguides also support higher order modes with losses negligible over these lengths ( transmission loss for TE 11 <0.05 dB over these distances in Cu wgs with similar diameters [11]), consequently, the alignment between the QCLs and the copper pipes represents the most critical step that has to be undertaken carefully. In fact, a small relative misalignment can lead to the excitation of higher order or mixed modes, yielding an output that would not be usable in many QCL applications [17][18][19], or could not be efficiently matched to a similar external waveguide. The critical alignment between the QCLs and the hollow waveguides has been carried out by using micrometer translators for both the wgs and the QCLs and an optical microscope for monitoring the relative distance.…”

Section: Fabricationmentioning

confidence: 99%

Hollow metallic waveguides integrated with terahertz quantum cascade lasers

Degl’Innocenti¹,

Shah²,

Jessop³

et al. 2014

Opt. Express

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Abstract:We present the realization of a compact, monolithically integrated arrangement of terahertz quantum cascade lasers with hollow metallic cylindrical waveguides. By directly mounting a copper pipe to the end facet of a double metal waveguide, it was possible to significantly improve the far field emission from such a sub-wavelength plasmonic mode, while preserving the characteristic performance of the laser. Careful alignment of the quantum cascade laser and the hollow waveguide is required in order to prevent the excitation of higher order/mixed modes as predicted with a high degree of accuracy by a theoretical model. Finally, this approach proved to be a superior method of beam shaping when compared to other in situ arrangements, such as a silicon hyper-hemispherical lens glued to the facet, which are presented. Ritchie, "Guiding a terahertz quantum cascade laser into a flexible silver-coated waveguide," J. Appl. Phys. 110(6), 063112 (2011). 16. S. Barbieri, J Alton, H. E. Beere, J. Fowler, E. H. Linfield, and D. A. Ritchie, "2.9 THz quantum cascade lasers operating up to 70 K in continuous wave," Appl.

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Section: Fabricationmentioning

confidence: 99%

Hollow metallic waveguides integrated with terahertz quantum cascade lasers

Degl’Innocenti¹,

Shah²,

Jessop³

et al. 2014

Opt. Express

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“…A growing attention in the scientific community has been directed to terahertz spectroscopic techniques, mostly time domain spectroscopy or confocal microscopy [12], as a non-invasive tool for measuring leaf water content [13, 14] and related quantities such as drought stress [15, 16] and dehydration kinetics [17]. The potential of THz absorption measurements was also demonstrated in the study of the hydration of biomolecules [18–20] and ions [21–24].…”

Section: Introductionmentioning

confidence: 99%

Non-invasive absolute measurement of leaf water content using terahertz quantum cascade lasers

et al. 2017

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BackgroundPlant water resource management is one of the main future challenges to fight recent climatic changes. The knowledge of the plant water content could be indispensable for water saving strategies. Terahertz spectroscopic techniques are particularly promising as a non-invasive tool for measuring leaf water content, thanks to the high predominance of the water contribution to the total leaf absorption. Terahertz quantum cascade lasers (THz QCL) are one of the most successful sources of THz radiation.ResultsHere we present a new method which improves the precision of THz techniques by combining a transmission measurement performed using a THz QCL source, with simple pictures of leaves taken by an optical camera. As a proof of principle, we performed transmission measurements on six plants of Vitis vinifera L. (cv “Colorino”). We found a linear law which relates the leaf water mass to the product between the leaf optical depth in the THz and the projected area. Results are in optimal agreement with the proposed law, which reproduces the experimental data with 95% accuracy.ConclusionsThis method may overcome the issues related to intra-variety heterogeneities and retrieve the leaf water mass in a fast, simple, and non-invasive way. In the future this technique could highlight different behaviours in preserving the water status during drought stress.

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“…Lately, there has been a growing trend in the field of plant physiology and characterisation of liquid to use THz time-domain spectroscopy (TDS) [11,22], which is considered a non-invasive technique, and has been deployed in the field of plant physiology to detect anomalies proactively. Moreover, it has an enormous potential to measure the leaf water status under certain conditions, such as drought stress [11,13,15,23,24] and dehydration kinetics [19]. In addition, THz-TDS technique can also investigate the structural behaviour and complex traits of leaves under any environment [14,19].…”

Section: Introductionmentioning

confidence: 99%

Characterization and Water Content Estimation Method of Living Plant Leaves Using Terahertz Waves

et al. 2019

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An increasing global aridification due to climate change has made the health monitoring of vegetation indispensable to maintaining the food supply chain. Cost-effective and smart irrigation systems are required not only to ensure the efficient distribution of water, but also to track the moisture of plant leaves, which is an important marker of the overall health of the plant. This paper presents a novel electromagnetic method to monitor the water content (WC) and characterisation in plant leaves using the absorption spectra of water molecules in the terahertz (THz) frequency for four consecutive days. We extracted the material properties of leaves of eight types of pot herbs from the scattering parameters, measured using a material characterisation kit in the frequency range of 0.75 to 1.1 THz. From the computed permittivity, it is deduced that the leaf specimens increasingly become transparent to the THz waves as they dry out with the passage of days. Moreover, the loss in weight and thickness of leaves were observed due to the natural evaporation of leaf moisture cells and change occurred in the morphology of fresh and water-stressed leaves. It is also illustrated that loss observed in WC on day 1 was in the range of 5% to 22%, and increased from 83.12% to 99.33% on day 4. Furthermore, we observed an exponential decaying trend in the peaks of the real part of the permittivity from day 1 to 4, which was reminiscent of the trend observed in the weight of all leaves. Thus, results in paper demonstrated that timely detection of water stress in leaves can help to take proactive action in relation to plants health monitoring, and for precision agriculture applications, which is of high importance to improve the overall productivity.

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Terahertz confocal microscopy with a quantum cascade laser source

Cited by 44 publications

References 20 publications

Hollow metallic waveguides integrated with terahertz quantum cascade lasers

Hollow metallic waveguides integrated with terahertz quantum cascade lasers

Non-invasive absolute measurement of leaf water content using terahertz quantum cascade lasers

Characterization and Water Content Estimation Method of Living Plant Leaves Using Terahertz Waves

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