The mid-infrared spectral range plays an increasingly important role in harnessing applications ranging from biodiagnostics to in-vivo sensing and food safety. This has led to the evolution of mid-infrared photonics from an emerging technology to an enabling tool in routine use catering to a wide range of real-world scenarios. Applications ranging from non-invasive exhaled breath analysis to the in-vivo assessment of cartilage damage or the detection of mycotoxins in food and feed confirm mid-infrared (MIR; 3-20 μm) photonics among the most flexible molecular sensing platforms nowadays available. This development has been catalyzed by the emergence of quantum and interband cascade laser (QCL, ICL) and LED technology providing miniaturized laser light sources based on quantum heterostructures that may be combined with frequency-matched waveguides/transducers for on-chip hybridization and/or integration toward IR-lab-on-chip systems.

For decades, TeraFETs have been used as THz and sub-THz detectors competing with commercial Schottky diode-based technology. More recently, short channel TeraFETs have been explored for THz vector detection measuring both the intensity and phase of the impinging THz or sub-THz radiation. We report on using TeraFETs as spectrometers, lineof- sight detectors, and frequency-to-digital converters. These applications use a single TeraFET excited at the gate-to-source and drain-to-source inputs, current-driven TeraFETs, or traveling wave multistage TeraFET amplifiers. Feeding the phase-shifted THz signals into the gate and source terminals of multistage TeraFET amplifiers greatly improves the response of the TeraFET spectrometer and enables the implementation of the frequency-to-digital converter using TeraFETs.

We present a multi-octave, mid-infrared supercontinuum source spanning from 3.6μm and extending into long-wave infrared region out to 11μm with an exceptionally high conversion efficiency of 8.2% and output power of 39 mW. These results were enabled by intra-pulse difference frequency generation involving a femtosecond Thulium doped fiber laser, an indium fluoride fiber and a zinc germanium phosphide crystal.

An on-chip spectropolarimeter is proposed based on gallium nitride polarization and spectral encoders. Polarization encoding is achieved via local strain engineering and valence-band mixing induced by asymmetric strain relaxation. Broadband polarization-sensitive photodetectors can replace linear polarizers to enable chip-scale implementation of a spectropolarimeter with the help of computational reconstructive algorithms.

Continuous progress in science, technology, and clean environmental regulations for energy requires low-power chip scale devices in sensing applications. Conventional trace gas sensing in the midinfrared region is highly sensitive. However, it requires a complex optomechanical setup that may not be suitable for wide-area deployments. This paper shows the development of new waveguide materials for near and mid-infrared silicon photonics ranging from 0.7 to 10 mm. These include amorphous semiconductors like Chalcogenide Glasses (ChGs) of Germanium-Selenium-Silicon (Ge-Se-S) elements with different compositions. UV-Vis measurements show the optical energy gap between 1.6 eV with high Se concentration to 3.8 eV, where Se is replaced by S in the compositions. ATRFTIR measurements show a high transmission spectrum ranging from 4000 to 400 cm^-1. We show the optical properties of such thin film materials in the broadband range of mid-infrared, suitable for fabricating waveguides and micro-resonator cavities for on-chip sensing applications.

Spectral sensing technology has rapidly evolved in recent years, with compact spectral sensors emerging as powerful tools for quality control and material analysis across diverse industrial and scientific domains. Compact spectral sensors offer significant advantages in terms of size, affordability, and versatility, making them an attractive choice for quality control and material analysis tasks. The state-of-the-art spectral sensors evaluated in this paper are sensors from Senorics (1200-1700nm, 16 channel) and from AMS (750-1050nm, 61 channel). The strengths and limitations of each sensor are evaluated, providing valuable insights for end-users, researchers, and engineers seeking to select the most suitable sensor for their specific application. Quality control and material analysis applications are the focus of this evaluation. This research underscores the key strengths and limitations of compact spectral sensors, and the potential for data fusion techniques to further enhance their capabilities. It highlights the role of these sensors in transforming quality control processes, enabling rapid and non-destructive material analysis, and ensuring compliance with stringent industry standards. The findings presented in this paper offer researchers, engineers, and practitioners a deeper understanding of the potential of the selected sensors across a range of applications. As we continue to harness these sensors for quality control and material analysis, we are on the path to achieving more efficient, reliable, and sustainable processes in a variety of industries.

Fourier Transform Near-Infrared (FT-NIR) spectroscopy, a powerful and versatile analytical technique, has found significant applications in Process Analysis technology. This non-invasive and rapid method harnesses the principles of near-infrared light absorption to deliver real-time insights into chemical composition, molecular structure, and physical properties of substances in a wide range of industrial processes. By virtue of its precision and adaptability, new Ethernet interface, the FT-NIR enables enhanced process control, quality assurance, and optimization across various industries, including pharmaceuticals, petrochemicals, food and beverage, and environmental monitoring. “

Quantum Dots (QDs) have been receiving significant attention due to their scientific interest (e.g., they were awarded the Nobel Prize in Chemistry last year) or their technological applications (e.g., television displays). Furthermore, many researchers find it intellectually appealing to work with Nobel Prize winning ideas. In this paper, the application of Quantum Dots (primarily) for detection of metal ions in water samples or in biological samples (e.g., blood syrum) will be described in detail and future directions will be discussed.

Terahertz plasmonic surface waves have attracted enormous attention even since the observation of extraordinary transmission of the terahertz waves in a periodic metallic array of subwavelength apertures. Quantitative analysis of the near-field behavior and contribution of surface plasmons to the transmission enhancement still remains challenging. By use of near-field scanning terahertz microscopy and numerical simulation, we study launching, propagation, and focusing of plasmonic surface waves with an ultimate goal of in-depth understanding the near-field characteristics of plasmonic terahertz surfaces waves.

Design considerations and technical challenges of a Sagnac-Fourier-Spectrometer (SAFOS) are reported, which is a Sagnac interferometer with an additional transmission grating. This causes two diffracted wave fronts to propagate in opposite directions along the common path. If the tilt of the wave fronts is chosen appropriately, they will form a Fizeau fringe pattern in the output arm. Via the spatial frequencies, this interferogram contains spectral information heterodyned around a central wavelength. By changing the grating constant and the dependent design parameters, high resolving power or broad spectral range can be accomplished. Also, the device can be calibrated with the radiation under test, that is, without an additional external light source.

We present further development of an eye-safe, invisible, stand-off technique designed for the detection of target chemicals in a single “Snapshot” frame, capable of chemically identifying moving targets. Broadband Fabry-Perot quantum cascade lasers (FP-QCLs) are employed in the LWIR (long-wave infrared) in the range of 8 to 12μm, to interrogate the spectral features from analytes of interest. We have developed a custom-built broadband laser source in the LWIR range. This “white” broadband laser source enables stand-off detection in a single snapshot frame. The transmission signals from target chemicals are spectrally extracted by an LWIR spectrometer based on the spatial heterodyne spectroscopy (SHS) technique. This manuscript will cover the implementation and optimization of an FP-QCL for this broadband spectroscopic application. We discuss the collection and processing of SHS images to extract spectral information. Finally, we present results of measurements to demonstrate the application of the method to spectroscopic identification of chemicals, including on moving targets.

Quantum Cascade Lasers (QCLs) provide a high-power, tunable source of coherent light at wavelengths from 3-12 microns. Light in this band excites vibrational modes of many molecules of interest across widely diverse fields of interest. Spectroscopic instruments using QCLs have the capability to make breakthrough observations across multiple disciplines. We discuss the technical capability of these laser sources as well as their instrumentalized imaging and liquid-phase detection systems. We review the recent applications of QCL-based spectroscopy using standalone compact laser sources, packaged liquid-phase spectrometers, and mid-IR microscopes. In particular, we focus on a recent application of QCL-based IR microscopes to quantify microplastics in water and identify the plastic type of each particle using hyperspectral imaging. We show that QCL-based IR hyperspectral imaging can detect particles <20 um in diameter and can differentiate between different plastic materials with high accuracy.

Since the discovery of graphene (a two dimensional material) by Andre Geim and Konstantin Novoselov (both of the University of Manchester, UK) for which they were awarded the 2010 Nobel Prize in Physics, graphene has been receiving significant attention primarily as an electronic material. More recently, we have been using modified graphene to collect Cr-species (e.g., Cr³⁺ or Cr⁶⁺) from lake water samples and to support the collected species on laboratory modified graphene. The concentration of the species extracted from the water samples and collected on the modified graphene oxide can be measured in the field using a portable, in-house developed, battery-operated microplasma and a portable fiber-optic spectrometer. Details will be discussed in this presentation.

This paper introduces a novel laser-based system designed for real-time Raman spectroscopy applied to in-line combustion diagnostics. While Raman spectroscopy is a well-established technique for solid and liquid analysis, its application to gas samples is challenging due to their low density, which limits the intensity of Raman scattering. To address this issue, our system utilizes a multipass cell, strategically designed to enhance signal generation and its collection. The instrument performs calibrated analysis, providing qualitative and quantitative information about gas composition. Depending by the application, the system can work with spectra integration time ranging from 0.15 s up to 10 s. This study has demonstrated that Raman spectroscopy can be a useful tool for combustion diagnostics, as it can operate fast enough to follow the time scale of combustion phenomena.

The Natural Gas (NG) sector is looking at the Hydrogen-enriched Natural Gas mixtures (H-NG) with growing interest. Hydrogen injections in the NG networks are expected to increase in the next years. Simultaneously, there is the requirement to constantly sample the composition and the thermodynamics properties of combustible blends. Raman spectroscopy is an intrinsic non-invasive approach for gas analysis. In addition, this technique is able to provide multiple-species analysis in a simultaneous way. An industrial-grade instrument, designed to operate directly on-site, has been developed. Its aim is to determine the NG and H-NG blends composition in an accurate and repeatable way, by referring to the OIML R 140 standard. The system is going forward in its industrialization by applying all the engineering steps useful to make it robust and easily replicable. The system laser source is a broadband multi-mode diode centered at 447nm with an optical power of 2W. The scattered radiation is collected by an appositely designed diffraction grating spectrometer and acquired by a 2D uncooled camera. The spectrometer guarantees Raman Stokes acquisition of the entire spectral region of interest without any mechanical movement. Three typical NG and one H-NG certified mixtures has been measured by placing the system in a climatic chamber. The results obtained during this validation show a high accuracy and repeatability in the overall temperature range by requiring only one calibration set carried out at room temperature. The calorific value, calculated by the measured gas mixture concentration, results within ±0.5% error in the full temperature range.

In this paper, the application of Artificial Intelligence (AI) and related topics (e.g., Machine Learning, Artificial Neural Networks (ANNs), deep learning) as they apply to analytic spectrometry (e.g., either using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), or a portable, battery-operated microplasma-OES) using a fiber-optic spectrometer) will be described, and the application of AI to teaching analytical atomic spectrometry will be outlined.

We have developed a miniaturized tele-operated unmanned ground imagery robot integrated with Raman Spectroscopy to allow forensic officers to gain early access to a hazardous scene to gather forensic evidence during the golden hour. This multi-terrain robot (named Seeker) has a dimension of 36 cm (L) x 36 cm (W) x 12 cm (H) and is designed for use in both open and confined spaces. The Raman spectroscopy module, which measures 17 cm (L) x 17 cm (W) x10 cm (H), consists of an 830 nm excitation laser, a compact non-cooled spectrometer, and an optical fiber probe. Feasibility tests were carried out on Seeker to remotely obtain Raman spectra of sulfur and trinitrotoluene (TNT) on spiked debris.

The detection of trace amounts of hazardous agents has become crucial for protection of human life, infrastructure and the environment. Single-particle mass spectrometry (SPMS) has proven to be a sensitive measurement technique for instantly revealing the chemical composition of individual, potentially harmful aerosol and dust particles. In this study, we focus on profiling non-volatile particles of explosive compounds in powdered form. It is reported, how the unique SPMS technology, based on (1) particle velocimetry and sizing, (2) sophisticated laser ionization and (3) bipolar time-of-flight mass spectrometry (TOF-MS) has been tailored and applied for the detection of individual particles of common explosive substances in the micro- and nanometer range. Out of more than 30 different types of military and home-made explosives, which were investigated in our recent laboratory measurements, the mass spectra of 12 commonly used explosives compounds are examined. Steps are described for automated and reliable identification of characteristic spectral markers of each of the explosives in their respective mass spectra.

The amount of end-of-life photovoltaic modules will increase significantly in the upcoming years. In order to enable a high-quality recycling process, innovative approaches to separate the module laminates layer by layer are required. In this work we use a combination of near-infrared spectroscopy (NIRS) and optical coherence tomography (OCT) to characterize the identity and dimensions of the individual layers within the multi-material composite of a PV module, especially the backsheet. NIRS is used to identify the polymer material types, while OCT measures the respective thickness of the layer. First results show that the combination of both techniques enables a precise qualitative and quantitative description of the layers of a PV module that can be used as an input for subsequent separation and recycling processes.

This study investigates the application of hyper-spectral imaging (HSI) for detecting polymer contaminants on glass substrates following photovoltaic (PV) recycling processes. HSI’s non-destructive and real-time capabilities are essential for ensuring the quality of separated PV components such as the glass pane. Experimental results demonstrate the precision of HSI in identifying polymer residues, leading to clean, uncontaminated glass suitable for complete re-use. Moreover, our work examines the challenges and future potential of HSI in contaminant detection, highlighting its importance as an in-line quality control tool in industrial recycling facilities.

As unexpectedly, the progress achieved in the area of spectroscopy is due to the rapid technological development particularly as a result of conversions supercontinuum (SC) light sources, into an instrument of the key importance. This paper is aimed at providing a detailed bibliometric map, showing the progress and gradual expansion of the application of SCI, in the sub-field of spectroscopy. By combing through information coming from prominent databases built over several decades, we reassure on identifying the main lines, the greatest studies in their aspect and also themes in which the majority of applications are found. Preliminary detection shows that by number there has been a visible spike in imprints pertaining the industry, as a telling sign of the raise SC is acquiring across the board. The geographic factor’s analysis shows a remarkable level of global marge, highlighting North America and Europe as key techno advancement leaders, contributors, and promoters. The SC family experiences applications across different fields as a result of their versatile nature, for which both advantages of wide spectral bandwidth and high brightness serves as an example. Examples of this kind have been benefitted from the improved spectral resolution and fast imaging rate offered by supercontinuum sources which are superior to those of normal continuous illumination sources. However, the integrating issues remain especially in the domain of source stability and systems tuning. Such research serves to emphasize the magnificent supercontinuum containing the elastic structures as the triggering element behind the modernization of the spectroscopic tools. Moreover, superconductivity’s presence implies the recognition of spectroscopy’s emerging areas of expertise, an aspect that could possibly be enhanced further by the incorporation of superconductivity. The paper intends to share information about the historical trends, present state of, and future prospects of supercontinuum assisted spectroscopy to researchers and the industry professionals through insights by following the process of charting the trajectory of SC.