Terahertz Spectroscopy for Gastrointestinal Cancer Diagnosis

In this chapter, we present a number of sensitive measurement modalities for the study and analysis of human cancer-affected colon and gastric tissue using terahertz (THz) spectroscopy. Considerable advancements have been reached in characterization of bio-tissue with some accuracy, although too dawn, and still long and exhaustive work have to be done towards well-established and reliable applications. The advent of the THz-time-domain spectroscopy (THz-TDS) test modality at a sub-picosecond time resolution has arguably fostered an intensive work in this field’s research line. The chapter addresses some basic theoretical aspects of this measurement modality with the presentation of general experimental laboratory setup diagrams for THz generation and detection, sample preparation aspects, samples optical parameters calculation procedures and data analysis

Multivariate analysis and artificial neural network approaches of near infrared spectroscopic data for non-destructive quality attributes prediction of Mango (Mangifera indica L.)

There is a need for fast and reliable quality and authenticity control tools of pharmaceutical ingredients. Among others, hormone containing drugs and foods are subject to scrutiny. In this study, terahertz (THz) spectroscopy and THz imaging are applied for the first time to analyze melatonin and its pharmaceutical product Circadin. Melatonin is a hormone found naturally in the human body, which is responsible for the regulation of sleep-wake cycles. In the THz frequency region between 1.5 THz and 4.5 THz, characteristic melatonin spectral features at 3.21 THz, and a weaker one at 4.20 THz, are observed allowing for a quantitative analysis within the final products. Spectroscopic THz imaging of different concentrations of Circadin and melatonin as an active pharmaceutical ingredient in prepared pellets is also performed, which permits spatial recognition of these different substances. These results indicate that THz spectroscopy and imaging can be an indispensable tool, complementing Raman and Fourier transform infrared spectroscopies, in order to provide quality control of dietary supplements and other pharmaceutical products

Short-length carbon nanotubes as building blocks for high dielectric constant materials in the terahertz range

Due to the high polarizability of finite-length carbon nanotubes (CNTs) in the quasi-static regime, they can be considered as building blocks for the fabrication of high dielectric constant material. Our theoretical estimations, based on an effective medium approach and solutions of a boundary value problem for individual CNT, predict that composite materials comprising short-length CNTs can have very high dielectric constants (up to 300) and low dielectric loss tangents (below 0.03) in the terahertz range. In order to prove this, 500–1000 nm thick films comprising single- and multi-walled CNTs of both long (0.5–2 μm) and short (0.1–0.4 μm) lengths have been fabricated. The analysis, based on the time-domain terahertz spectroscopy in the range 0.2–1.0 THz, demonstrated a decrease in the dielectric loss tangents of the CNT-based materials with a reduction in CNT length. In the terahertz range, the films comprising short-length CNTs had a relative effective permittivity with a large real part (25–136) and dielectric loss tangent (0.35–0.60)

Principles for single-pixel terahertz imaging based on the engineering of illuminating and collecting nonparaxial diffractive optics

The art of light engineering unveils a world of possibilities through the meticulous manipulation of photonic properties such as intensity, phase, and polarization. The precise control over these optical properties under various conditions finds application in fields spanning communication, light-matter interactions, laser direct writing, and imaging, enriching our technological landscape. In this study, we embark on a journey to establish a rational framework for the design and assembly of nonparaxial THz imaging systems. Our focus centers on a lensless photonic system composed solely of flat-silicon diffractive optics. These elements include the high-resistivity silicon-based nonparaxial Fresnel zone plate, the Fibonacci lens, the Bessel axicon, and the Airy zone plate, all meticulously crafted using laser ablation technology. A systematic exploration of these flat elements in various combinations sheds light on their strengths and weaknesses. Our endeavor extends to the practical application of these optical components, where they illuminate samples and capture the light scattered from these raster-scanned samples using single-pixel detectors. Through a comprehensive examination, we evaluate imaging systems across diverse metrics that include contrast, resolution, depth of field and focus. This multifaceted approach allows us to distill rational design principles for the optimal assembly of THz imaging setups. The findings of this research chart an exciting course toward the development of compact, user-friendly THz imaging systems where sensors and passive optical elements seamlessly integrate into a single chip. These innovations not only enhance capabilities in THz imaging but also pave the way for novel applications, ushering in a new encouraging era of advanced THz photonic technology.Comment: 26 page

Shielding effects in thin films of carbon nanotubes within microwave range

The electromagnetic shielding properties of thin films comprising different types of carbon nanotubes (CNTs) were analysed in the microwave frequency range (26–36 GHz). A comparative analysis of the shielding properties was achieved for films based on long and short single-, double- and multi-walled CNTs. The experimental results proved that long-length single-walled CNTs demonstrate the highest interaction with the electromagnetic (EM) field, thereby providing the best shielding efficiency. At the same time, double-walled CNTs demonstrate a higher level of absorption ability (50%) along with the overall high EM shielding efficiency (88%), which makes them attractive for using in nanoelectronics screens as they produce the smallest secondary EM pollution

Polarized photoreflectance and photoluminescence spectroscopy of InGaAs/GaAs quantum rods grown with As2 and As4 sources

We report photoreflectance (PR) and photoluminescence (PL) investigations of the electronic and polarization properties of different aspect ratio (height/diameter) InGaAs quantum rods (QRs) embedded in InGaAs quantum wells (QWs). These nanostructures were grown by molecular beam epitaxy using As2 or As4 sources. The impact of the As source on the spectral and polarization features of the QR- and QW-related interband transitions was investigated and explained in terms of the carrier confinement effects caused by variation of composition contrast between the QR material and the surrounding well. Polarized PR and PL measurements reveal that the polarization has a preferential direction along the [ 110] crystal axis with a large optical anisotropy of about 60% in the (001) plane for high aspect ratio (4.1:1) InGaAs QRs. As a result, in PL spectra, the transverse magnetic mode dominated (110)-cleaved surfaces (TM[001] > TE[110]), whereas the transverse electric mode prevailed for (110)-cleaved surfaces (TM[001] < TE[110] ¯ ). This strong optical anisotropy in the (001) plane is interpreted in terms of the hole wavefunction orientation along the [ 110] direction for high aspect ratio QRs