Terahertz fingerprinting in presence of quasi-ballistic scattering

Kaushik, Mayank; Ng, Brian W.-H.; Fischer, Bernd; Abbott, Derek

doi:10.1063/1.4745182

Cited by 13 publications

(7 citation statements)

References 22 publications

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“…Therefore, estimating the scattering contribution in the extinction coefficient of materials with characteristic absorption signatures requires more advanced computational approaches. Moreover, previous studies have mainly focused on estimating the scattering loss in the ballistic regime 29,30,[32][33][34][35][36] , and the effects of volume scattering on diffuse THz fields have not been investigated. Here, we present a robust computational approach based on the wavelet multiresolution analysis (MRA) of the THz extinction spectra along with the kurtosis and skewness of the spectral images, presented as a new spectroscopy concept dubbed the bimodality spectrum, to reliably identify the characteristic resonant frequencies using the scattered THz waves in both ballistic and diffusive regimes.…”

Section: Scattering Mitigation Through Wavelets and Bimodality Spectral Analysismentioning

confidence: 99%

“…THz-TDS techniques mostly use the ballistic and quasi-ballistic portion of the transmitted THz light 15 . They either ignore the diffused THz waves 29,30 or employ them only by averaging with the ballistic forward-scattered fields 31 . For example, the effect of volume scattering in pressed pellets of materials were studied using forward-scattered THz electric-field transmission measurements 29,30,[32][33][34][35][36] .…”

Section: Introductionmentioning

confidence: 99%

“…They either ignore the diffused THz waves 29,30 or employ them only by averaging with the ballistic forward-scattered fields 31 . For example, the effect of volume scattering in pressed pellets of materials were studied using forward-scattered THz electric-field transmission measurements 29,30,[32][33][34][35][36] . However, utilization of only diffusely-scattered waves critical in studying hostile and uncooperative samples, or in detection geometries without access to the narrow cone of the forward-scattered beams, has not been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Diffuse Terahertz Spectroscopy in Turbid Media Using a Wavelet-Based Bimodality Spectral Analysis

Khani

Osman

Arbab

2021

Preprint

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Current terahertz (THz) spectroscopy techniques only use the coherent light beam for spectral imaging. In the presence of electromagnetic scattering, however, the scattering-mitigated incoherent beams allow for flexible emitter-detector geometries, which enable applications such as seeing through turbid media. Despite this potential, THz spectroscopy using diffuse waves has not been demonstrated. The main obstacles are the very poor signal to noise ratios of the diffused fields and the resonance-like spectral artifacts due to multiple Mie scattering events that obscure the material absorption signatures. In this work, we demonstrate diffuse THz spectroscopy of a heterogeneous sample through turbid media using a novel technique based on the wavelet multiresolution analysis and the bimodality coefficient spectrum, which we define here for the first time using the skewness and kurtosis of the spectral images. The proposed method yields broadband and simultaneous material characterization at detection angles as high as 90o with respect to the incident beam. We determined the accuracy of the wavelet-based diffuse spectroscopy at oblique detection angles, by evaluating the area under the Receiver Operating Characteristic (ROC) curves, to be higher than 95%. This technique is agnostic to any a priori information on the spectral signatures of the sample materials or the characteristics of the scattering medium, and can be expanded for other broadband spectroscopic modalities.

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Section: Scattering Mitigation Through Wavelets and Bimodality Spectral Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diffuse Terahertz Spectroscopy in Turbid Media Using a Wavelet-Based Bimodality Spectral Analysis

Khani

Osman

Arbab

2021

Preprint

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“…But the fast rise of the total losses with frequency can decrease the spectral range of measurements. Theoretical modeling of the scattering effects in the pellets was done in a number of works [5]- [10] and the mitigation procedures were proposed, enabling one to discern the pure absorption "fingerprint" without the continuous background. But the appearance of a uniform background is not the only manifestation of the scattering effects.…”

mentioning

confidence: 99%

Scattering Effects in Terahertz Wave Spectroscopy of Granulated Solids

Kornienko

Ахмеджанов

Ilyakov

et al. 2015

IEEE Trans. THz Sci. Technol.

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Applications of terahertz spectroscopy methods to granulated solids are substantially constrained by the effects of scattering of the incident terahertz waves by spatial heterogeneities of a sample. The experimental results obtained by means of terahertz time-domain spectroscopy are reported for the samples of granulated 2, 4-dinitrotoluene and alpha-lactose without any special filling. We show that in samples of the same substance, but prepared in a different manner, the overall increase of the background extinction with frequency and appearance of additional extinction maxima can obscure the true absorption features of the material. In samples with large grain size, of order of 400 m, a complicated irregular spectral structure is observed instead of a fingerprint maxima at 1.37 THz for alpha-lactose and at 1.08 THz for 2,4-dinitrotoluene. At higher frequencies no true spectral fingerprints are clearly seen in the raw experimental spectra of all the samples with the grain sizes of 130 m and more. The influence of grain size, air-filling factor and the dispersion properties of the materials is studied. Theoretical analysis is made with the use of Mie theory in simplifying approximations and taking into account interference between the waves transmitted through a porous sample. It has been shown that the scattering-induced masking effects can be properly simulated even for the air-filled objects with initially unknown spatial and dispersion parameters. The procedure of eliminating the influence of scattering effects from the raw spectral data is proposed. Detection of true high-frequency spectral fingerprints is demonstrated using this procedure for various grain sizes up to 400 m.Index Terms-Electromagnetic interference, electromagnetic propagation in absorbing media, submillimeter-wave measurements, submillimeter-wave propagation.

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“…[1][2][3][4][5][6][7] However, the construction of a frequency-agile THz systems is hindered by the lack of high-performance THz devices. To control the THz frequency signal, metamaterial-based devices have been investigated.…”

mentioning

confidence: 99%

Terahertz filter integrated with a subwavelength structured antireflection coating

Woo

Kim

et al. 2015

AIP Advances

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Micro-pyramid shaped subwavelength structures (SWSs) were integrated on both sides of a terahertz (THz) filter by means of stamping methods. Two silicon-based stamping molds fabricated via crystallographic wet etching were utilized to replicate SWSs onto cyclo-olefin copolymer (COC) films coated onto both sides of a THz filter at the same time. The SWSs act as an broadband antireflection coating to reduce the surface reflection loss in a frequency range of 0.2 THz to 1.4 THz. Compared to a THz filter without SWSs, the filter integrated with double-sided SWSs exhibits a low standing wave ratio inside the substrate and THz signal transmission enhancement of up to 10.8%.

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Terahertz fingerprinting in presence of quasi-ballistic scattering

Cited by 13 publications

References 22 publications

Diffuse Terahertz Spectroscopy in Turbid Media Using a Wavelet-Based Bimodality Spectral Analysis

Diffuse Terahertz Spectroscopy in Turbid Media Using a Wavelet-Based Bimodality Spectral Analysis

Scattering Effects in Terahertz Wave Spectroscopy of Granulated Solids

Terahertz filter integrated with a subwavelength structured antireflection coating

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