Optical Effects at projection measurements for Terahertz tomography

Brahm, A.; Wilms, A.; Tymoshchuk, M.; Großmann, Constanze; Notni, Gunther; Tünnermann, Andreas

doi:10.1016/j.optlastec.2014.02.011

Cited by 20 publications

(8 citation statements)

References 22 publications

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“…In the center (position 15) of the projection a reduced absorption peak can be observed. In the terahertz spectral region, this kind of projection shape is typical for a cylindric object, and has been observed several times [16][17][18]. Here, the plateaus do not represent regions of the sample object with a high absorption coefficient, they are rather the result of combined refraction and reflection effects.…”

Section: Resultsmentioning

confidence: 85%

“…Optical effects like refraction, reflection and diffraction influence the measured projections and can lead to distortions in the reconstructed image. For this reason the effects of refraction on the measured projections is discussed using ray tracing simulations in several articles [16,17]. Therefore, special image reconstruction algorithms, which for example compensate the influence of refraction for a cylindrical object, have been developed [18].…”

Section: Introductionmentioning

confidence: 99%

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2D tomographic terahertz imaging using a single pixel detector

2018

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A 2D tomographic terahertz imaging set-up using a single pixel imaging approach is realized, where a liquid helium cooled bolometer is utilized as a bucket detector and a mercury-arc lamp serves as a broadband terahertz source. The different patterns of the terahertz radiation, which are necessary for the single pixel imaging approach, are realized by spatially addressed photodoping of a high resistivity float zone silicon window, employing a near-infrared laser diode, which is spatially modulated by a digital micromirror device. The two investigated sample objects have cylindrical and cuboid shapes and consist of polypropylene. Both sample shapes cause strong influences of refraction, reflection and diffraction, which distort the measured projections and thus have to be considered in the tomographic reconstruction. In order to consider these effects, a model is developed which combines refraction and diffraction effects by a hybrid approach using ray tracing and scalar diffraction theory yielding finally projections of the sample objects. These simulated projections are compared to the measured projections and show a good agreement between the experimental results and the developed model. In accordance with this result, an optimization problem is formulated, which offers an approach for tomographic reconstruction using the developed model.

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Section: Resultsmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

2D tomographic terahertz imaging using a single pixel detector

2018

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“…However, such surface and volume measurements only quantify the object ROIs which have been reconstructed from radiographs. Since THz waves suffer from multiple optical effects, [19][20][21][22] contrast in low-absorption parts of the object becomes negligible. Then, the averaging performed during the tomographic reconstruction leads to almost invisible ROIs (corresponding to the object parts which are very transparent to THz waves on several viewing angles) even if these ROIs seem visible in the projections.…”

Section: Quantitative Analysismentioning

confidence: 99%

Expectation maximisation algorithms for terahertz transmission tomography

2014

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International audienceTerahertz (THz) tomography is a recently developed imaging technique allowing 3D inspection of opaque objects. In this paper, we develop an ordered subsets convex algorithm for THz transmission tomography (THz-OSC). Since the reconstruction quality is highly depending on the THz beam energy, we investigate afterwards a multienergy version of the algorithm in order to provide a more accurate reconstruction of the acquired sample. This multi-energy approach is validated by reconstructing data from tomographic acquisitions measured with a 84/287 GHz transmission scanner. Then we discuss how this dual-energy approach could be able to extract physical properties of acquired samples in addition to improving 3D reconstruction

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“…They compared the experimental results with the numerical results obtained by the geometrical optical ray-tracing method, achieving good agreement. Paramonov et al 8 repeated the experiment of the cylinder made of polyetheretherketon in Brahm et al 7 by using ray optics and obtained good and consistent results. Tepe et al 9 proposed algorithms that take into account the main physical effects (reflection and refraction), leading to an improvement in the imaging distortion problem.…”

Section: Introductionmentioning

confidence: 96%

Equivalent source of reflector in finite‐different time‐domain for rapid analysis of corner scattering in terahertz computed tomography imaging

Feng,

Cha,

Shi

et al. 2024

Micro & Optical Tech Letters

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We propose the equivalent source of reflector in finite‐different time‐domain (ESR‐FDTD) for rapid analysis of corner scattering in terahertz computed tomography (THz‐CT) imaging. The ESR‐FDTD is used instead of the reflector in the THz‐CT imaging system, which can significantly reduce the computational domain of the THz‐CT imaging system and effectively reduce the computational time and memory usage. The electric field distribution of the beam reflected by the reflector and that of the beam radiated from the ESR of the reflector are compared, and the results show that the electric field distributions of the reflector and its ESR are almost the same. The results of the corner scattering show that the phenomenon of corner scattering does not fully satisfy the behaviors of reflection and refraction. Therefore, the corner scattering cannot be accurately analyzed by the ray‐tracing method.

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Optical Effects at projection measurements for Terahertz tomography

Cited by 20 publications

References 22 publications

2D tomographic terahertz imaging using a single pixel detector

2D tomographic terahertz imaging using a single pixel detector

Expectation maximisation algorithms for terahertz transmission tomography

Equivalent source of reflector in finite‐different time‐domain for rapid analysis of corner scattering in terahertz computed tomography imaging

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