mid-IR Range Research Articles

Vibrational spectroscopy: A novel technique changing the face of clinical diagnosis

The application of spectroscopy to provide insight to biological questions bothering on pathology in plant and animal tissues is a rapidly growing field known as biospectroscopy. Biospectroscopy has significantly changed the face of biological and toxicological research, from clinical diagnosis to environmental toxicology. Techniques involved have become potential tools for non-invasive optical tissue diagnosis and have been applied to study a wide variety of pathologic states. Cellular biomolecules absorb the mid-IR (λ = 2 -20 µm) via vibrational transitions that are derived from individual chemical bonds. Within the mid-IR range, 1800 – 900 cm-1 is regarded as the biochemical-cell fingerprint region, because it contains the fundamental vibrational modes of the structures present in biological specimens. The vibrational modes of key chemical bonds may thus be exploited to understand intracellular mechanisms as the biochemical-cell fingerprint of the material under study, is produced with direct association between peaks and chemical bonds. What makes it important for toxicological research in developing countries? 1) The relative simplicity of the technique with regards to the equipment 2) Ease of sample preparation/handling 3) Low cost and potentially reagent free. This technique will prove particularly useful in situations where a broad spectrum, exploratory Tox-Screen is required to observe the effect of a compound on a variety of biomolecules.

Photonic meta-switch based on phase change and catenary-enabled continuous phase regulation

Aiming at the characteristics of passive and discrete phase regulations inherent in current metasurfaces, we combine optimized isowidth catenary with non-volatile phase change dielectrics and explore a type of bistable phase-change-based wavefront meta-switch of continuous phase tuning and active switching. First, the switchable wavefront deflector is demonstrated in the mid-IR range between 9 µm and 10 µm. Upon phase transition between crystalline state and amorphous state, the incident wave can be switched into anomalous reflection and regular reflection, i.e. the “on” state and “off ” state of wave deflection. Further, a type of dynamically tunable Bessel beam switch is demonstrated. In the amorphous state, the polarization conversion efficiency approaches to 100% with an incident wave of 9.6 µm in wavelength. Therefore, the normal geometrical phase and the second-order Bessel focus are switched “on”. However, the cross-polarization and geometrical phase are switched “off ” upon phase changing into crystallized state. Intrinsically, non-dispersive spin-orbit interaction ensures that this kind of device possesses the broadband characteristics. Such a devise has great potential applications in active optoelectronic integration, optical communications, etc.

Взаимодействие фемтосекундного лазерного излучения с халькогенидными стеклами различного состава

The interaction of femtosecond laser radiation with a wavelength of 1030 nm with chalcogenide glasses of various compositions has been studied. The dependence of the optical transmission of chalcogenide glasses on the pulse energy and frequency has been experimentally established. The compositions of glasses for their use as an optical medium for laser micromachining in the infrared range have been established. It is shown that Ge7Se93 glass is the most suitable optical medium for spectral studies of diamond in the near and mid-IR range.

High Energy Pulse Amplification in Mid-IR Range Using Er:ZBLAN Fibers

High Energy Pulse Amplification in Mid-IR Range Using Er:ZBLAN Fibers

A solar flare driven by thermal conduction observed in mid-infrared

Context. The mid-infrared (mid-IR) range has been mostly unexplored for the investigation of solar flares. It is only recently that new mid-IR flare observations have begun opening a new window into the response and evolution of the solar chromosphere. These new observations have been mostly performed by the AR30T and BR30T telescopes that are operating in Argentina and Brazil, respectively. Aims. We present the analysis of SOL2019-05-15T19:24, a GOES class C2.0 solar flare observed at 30 THz (10 μm) by the ground-based telescope AR30T. Our aim is to characterize the evolution of the flaring atmosphere and the energy transport mechanism in the context of mid-IR emission. Methods. We performed a multi-wavelength analysis of the event by complementing the mid-IR data with diverse ground- and space-based data from the Solar Dynamics Observatory (SDO), the H-α Solar Telescope for Argentina, and the Expanded Owens Valley Solar Array (EOVSA). Our study includes the analysis of the magnetic field evolution of the flaring region and of the development of the flare. Results. The mid-IR images from AR30T show two bright and compact flare sources that are spatially associated with the flare kernels observed in ultraviolet (UV) by SDO. We confirm that the temporal association between mid-IR and UV fluxes previously reported for strong flares is also observed for this small flare. The EOVSA microwave data revealed flare spectra consistent with thermal free-free emission, which lead us to dismiss the existence of a significant number of non-thermal electrons. We thus consider thermal conduction as the primary mechanism responsible for energy transport. Our estimates for the thermal conduction energy and total radiated energy fall within the same order of magnitude, reinforcing our conclusions.

Modelling of power characteristics of CW OPO for mid-IR range

Modelling of power characteristics of CW OPO for mid-IR range

Octave-spanning low-loss mid-IR waveguides based on semiconductor-loaded plasmonics

Plasmonic waveguides are crucial building blocks for integrated on-chip mid-infrared (mid-IR) sensors, which have recently attracted great interest as a sensing platform to target enhanced molecular sensing. However, while hosting a wide range of applications from spectroscopy to telecommunication, the mid-IR lacks suitable broadband solutions that provide monolithic integration with III-V materials. This work reports a novel concept based on hybrid semiconductor-metal surface plasmon polariton waveguides, which result in experimentally demonstrated low loss and broadband devices. Composed of a thin germanium slab on top of a gold layer, the waveguiding properties can be directly controlled by changing the geometrical parameters. The measured losses of our devices are as low as 6.73 dB/mm at 9.12 µm and remain <15 dB/mm in the mid-IR range of 5.6–11.2 µm. The octave-spanning capability of the waveguides makes them ideal candidates for combination with broadband mid-IR quantum cascade laser frequency combs and integrated spectroscopic sensors.

Label-free spectroscopic characterization of exosomes reveals cancer cell differentiation

Exosomes (EXOs) are considered an exceptionally promising source of cancer biomarkers for personalized medicine and liquid biopsy. Despite this potential, the EXOs translation process in diagnostics is still at its birth, and the development of reliable and reproducible methods for their characterization is highly demanded. Fourier Transform Infrared (FTIR) Spectroscopy is perfectly suited for this purpose, as it can provide a label-free biochemical profile of EXOs in terms of lipid, protein, and nucleic acid content. Here we evaluated the applicability of FTIR spectroscopy to the study of cancer-derived EXOs as a function of cell differentiation. For this purpose, we used N-acetyl-l-Cysteine (NAC) to induce a controlled differentiation in human colon carcinoma cells from a proliferative mesenchymal morphology to a less invasive epithelial phenotype, as measured with fluorescence and electron microscopy. EXOs derived from cells with different phenotypes showed significant variation in the relative intensity of the amide I-II and CH-stretching bands in the mid-IR range, indicating the spectroscopic lipid/protein ratio as an effective classification parameter. Additionally, we showed that different cell phenotypes are associated with a shape modification in these spectral bands that can be automatically detected by combining Principal Component Analysis (PCA) with Linear Discriminant Analysis (LDA).On the one hand, our study confirms that an FTIR analysis of EXOs allows scientists to precisely detect modifications occurring at the parental cell level; on the other hand, it unveils a set of effective spectral biomarkers able to monitoring cell changes from a mesenchymal to an epithelial phenotype, a clinically valuable piece of information considering that the epithelial-to-mesenchymal transition is a key step in the metastatic process.

Application of Optical Quality Control Technologies in the Dairy Industry: An Overview

Sustainable development of the agricultural industry, in particular, the production of milk and feed for farm animals, requires accurate, fast, and non-invasive diagnostic tools. Currently, there is a rapid development of a number of analytical methods and approaches that meet these requirements. Infrared spectrometry in the near and mid-IR range is especially widespread. Progress has been made not only in the physical methods of carrying out measurements, but significant advances have also been achieved in the development of mathematical processing of the received signals. This review is devoted to the comparison of modern methods and devices used to control the quality of milk and feed for farm animals.

All-fiber ultrafast amplifier at 1.9\xa0\u03bcm based on thulium-doped normal dispersion fiber and LMA fiber compressor

The duration reduction and the peak power increase of ultrashort pulses generated by all-fiber sources at a wavelength of 1.9,upmu hbox {m} are urgent tasks. Finding an effective and easy way to improve these characteristics of ultrafast lasers can allow a broad implementation of wideband coherent supercontinuum sources in the mid-IR range required for various applications. As an alternative approach to sub-100 fs pulse generation, we present an ultrafast all-fiber amplifier based on a normal-dispersion germanosilicate thulium-doped active fiber and a large-mode-area silica-fiber compressor. The output pulses have the following characteristics: the central wavelength of 1.9,upmu hbox {m}, the repetition rate of 23.8 MHz, the energy per pulse period of 25 nJ, the average power of 600 mW, and a random output polarization. The pulse intensity and phase profiles were measured via the second-harmonic-generation frequency-resolved optical gating technique for a linearly polarized pulse. The linearly polarized pulse has a duration of 71 fs and a peak power of 128.7 kW. The maximum estimated peak power for all polarizations is 220 kW. The dynamics of ultrashort-pulse propagation in the amplifier were analyzed using numerical simulations.

Strain-modified effective two-band model for calculating the conduction band structure of strain-compensated quantum cascade lasers: effect of strain and remote band on the electron effective mass and nonparabolicity parameter

We propose a strain-modified effective two-band model to calculate the conduction band (CB) structure of strain-compensated quantum cascade lasers (QCLs). The proposed model can consider the effect of strain and remote band (RB) on the band-edge energy, electron effective mass, and nonparabolicity parameter although the currently used empirical two-band model can be applicable to only the unstrained QCLs. Based on the three-band second-order k·p Hamiltonian along with the Pikus-Bir Hamiltonian, analytical formula for the electron effective mass and nonparabolicity parameter are derived at the zone center, where the effects of strain and RB interaction are included. Then, the three-band first-order k·p Hamiltonian is reduced to the strain-modified effective two-band Hamiltonian, where the effective Kane energy, determined by the electron effective mass and nonparabolicity parameter, is used to include the nonparabolicity of the CB. By numerically solving the proposed strain-modified effective two-band model based on the finite difference method, we calculate the CB structure of several strain-compensated or unstrained QCLs in the mid-IR and terahertz range and predict their lasing wavelengths, which are well matched with the measured values in the literatures.

On the spectroscopic investigation of stamp inks using ATR-FTIR and chemometrics: Application in forensic document examination

The identification and differentiation of stamp inks can be a crucial aspect to establish the authenticity of questioned documents, and thus plays a vital role in judicial expertise. Herein, 16 brands of blue stamp inks and 12 brands of red stamp inks have been investigated using Attenuated Total Reflectance – Fourier Transform Infrared (ATR FT-IR) Spectroscopy in the mid-IR range. Stamp inks of different brands were differentiated using visual inspection of spectra with discrimination power of 96.6% and 93.9% for blue and red stamp inks respectively. To get enhanced and better discrimination power, chemometric tools such as PCA, PCA-LDA, and PLS-DA were applied, which provided satisfactory results with higher accuracy rate. Further, to check the influence of substrates, imprinted stamp inks on different papers were also analyzed and results have been discussed. Henceforth, the obtained results in the current study illustrates that the technique ATR FT-IR spectroscopy is a sensitive and reliable tool with minimal sample preparation requirements to identify and differentiate different manufactures of stamp inks, thus extends a novel approach to judge the document’s authenticity.

Ultra-Low-Loss Mid-Infrared Plasmonic Waveguides Based on Multilayer Graphene Metamaterials.

Manipulating optical signals in the mid-infrared (mid-IR) range is a highly desired task for applications in chemical sensing, thermal imaging, and subwavelength optical waveguiding. To guide highly confined mid-IR light in photonic chips, graphene-based plasmonics capable of breaking the optical diffraction limit offer a promising solution. However, the propagation lengths of these materials are, to date, limited to approximately 10 µm at the working frequency f = 20 THz. In this study, we proposed a waveguide structure consisting of multilayer graphene metamaterials (MLGMTs). The MLGMTs support the fundamental volume plasmon polariton mode by coupling plasmon polaritons at individual graphene sheets over a silicon nano-rib structure. Benefiting from the high conductivity of the MLGMTs, the guided mode shows ultralow loss compared with that of conventional graphene-based plasmonic waveguides at comparable mode sizes. The proposed design demonstrated propagation lengths of approximately 20 µm (four times the current limitations) at an extremely tight mode area of 10−6 A0, where A0 is the diffraction-limited mode area. The dependence of modal characteristics on geometry and material parameters are investigated in detail to identify optimal device performance. Moreover, fabrication imperfections are also addressed to evaluate the robustness of the proposed structure. Moreover, the crosstalk between two adjacent present waveguides is also investigated to demonstrate the high mode confinement to realize high-density on-chip devices. The present design offers a potential waveguiding approach for building tunable and large-area photonic integrated circuits.

Extraordinary optical transmission in silicon nanoholes

In this work, for the first time, a study was conducted of the existence of Extraordinary Optical Transmission (EOT) in Silicon (Si) thin films with subwavelength holes array and high excess carrier concentration. Typically EOT is studied in opaque perforated metal films. Using Si would bring EOT and its many applications to the silicon photonics realm and the mid-IR range. Since Si thin film is a semi-transparent film in mid-IR, a generalization was proposed of the normalized transmission metric used in literature for EOT studies in opaque films. The plasma dispersion effect was introduced into the studied perforated Si film through either doping or carriers’ generation. Careful consideration for the differences in optical response modeling in both cases was given. Full-wave simulation and analysis showed an enhanced transmission when using Si with excess carriers, mimicking the enhancement reported in perforated metallic films. EOT was found in the mid-IR instead of the visible range which is the case in metallic films. The case of Si with generated excess carriers showed a mid-IR EOT peak reaching 157% around 6.68 µm, while the phosphorus-doped Si case showed a transmission enhancement of 152% around 8.6 µm. The effect of varying the holes’ dimensions and generated carriers’ concentration on the transmission was studied. The analogy of the relation between the fundamental mode cutoff and the EOT peak wavelength in the case of Si to the case of metal such as silver was studied and verified. The perforated Si thin film transmission sensitivity for a change in the refractive index of the holes and surroundings material was investigated. Also, a study of the device potential in sensing the hole and surroundings materials that have almost the same refractive index yet with different absorption fingerprints was performed as well.

Methodology for identifying gaseous constituents of the atmosphere

Methodology for the analysis of concentrations of gaseous composite of atmosphere by the corresponding infrared (IR) spectrum, measured with the help of trajectory spectroradiometers (TSR) is observed. The developed algorithm for mathematical processing of the measurement results is briefly described, including the detection and estimation of the concentrations of the sought gases using the notch filtration of their spectral components, which makes it possible to significantly reduce the concentration identification error. The spectra of various substances in the mid-IR range are considered, and the results of approbation of the technique based on the TSR model with an external high-temperature radiation source on a 1 m path are presented.

Laser-based inactivation of pathogenic microorganisms

In the context of studying the possibility of inactivation of pathogenic microorganisms, the dynamic transmission spectra of femtosecond laser radiation in the mid-IR range by bacteria of the Pseudomonaus aeruginosa culture planted on a silicon substrate were investigated. Irradiation revealed a blue shift in the characteristic absorption bands of bacteria, indicating the breaking of hydrogen bonds responsible for the formation of the secondary and tertiary structure of the proteins.

Ultrawide shifting of the laser pulse wavelength in a multicore tellurite fiber with two zero-dispersion wavelengths

The generation of Raman solitons in the mid-IR range in a multicore fiber with two zero-dispersion wavelengths is studied analytically and numerically. The estimate for the maximum shift of the Raman soliton wavelength depending on the parameters of the media dispersion, the frequency-dependent losses, and the nonlinearity decreasing is obtained, which is in good agreement with the results of numerical simulation. A realistic design of a 10-core fiber made of a pair of compatible glasses is proposed for the Raman shift of the wavelength of soliton pulses propagating in an out-of-phase mode. The nonlinear dynamics of a laser pulse, specified at the wavelength of $2.3\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$, energy of 1.5 nJ, and duration of 100 fs, during propagation in a fiber with this design, is studied numerically. The generation of Raman solitons in the mid-IR range at wavelengths exceeding $4\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$, as well as dispersion waves in the $5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ range, emitted by a soliton when approaching the second zero-dispersion wavelength, is demonstrated.

Full spectrum 2D IR spectroscopy reveals below-gap absorption and phonon dynamics in the mid-IR bandgap semiconductor InAs.

While the mid-infrared spectral region spans more than 3000cm-1, ultrafast mid-IR spectroscopies are normally limited to the spectral bandwidth that can be generated in optical parametric amplifiers-typically a few hundred cm-1. As such, the spectral coverage in conventional two dimensional infrared (2D IR) spectroscopy captures only about 1% of the full potential 2D mid-IR spectrum. Here, we present 2D IR spectra using a continuum source as both the excitation and probe pulses, thus capturing close to the full 2D IR spectrum. While the continuum pulses span the entire mid-IR range, they are currently too weak to efficiently excite molecular vibrational modes but strong enough to induce electronic responses and excite phonons in semiconductors. We demonstrate the full spectrum 2D IR spectroscopy of the mid-IR bandgap semiconductor indium arsenide with a bandgap at 2855cm-1. The measured response extends far below the bandgap and is due to field-induced band-shifting, causing probe absorption below the bandgap. While the band-shifting induces an instantaneous response that exists only during pulse overlap, the 2D IR spectra reveal additional off-diagonal features that decay on longer timescales. These longer-lived off-diagonal features result from coherent phonons excited via a Raman-like process at specific excitation frequencies. This study illustrates that the full spectrum 2D IR spectroscopy of electronic states in the mid-IR is possible with current continuum pulse technology and is effective in characterizing semiconductor properties.

Time-encoded mid-infrared Fourier-domain optical coherence tomography.

We report on a technically simple approach to achieve high-resolution and high-sensitivity Fourier-domain optical coherence tomography (OCT) imaging in the mid-infrared (mid-IR) range. The proposed OCT system employs an InF3 supercontinuum source. A specially designed dispersive scanning spectrometer based on a single InAsSb point detector is employed for detection. The spectrometer enables structural OCT imaging in the spectral range from 3140 nm to 4190 nm with a characteristic sensitivity of over 80 dB and an axial resolution below 8µm. The capabilities of the system are demonstrated for imaging of porous ceramic samples and transition-stage green parts fabricated using an emerging method of lithography-based ceramic manufacturing. Additionally, we demonstrate the performance and flexibility of the system by OCT imaging using an inexpensive low-power (average power of 16 mW above 3µm wavelength) mid-IR supercontinuum source.

Mid-IR Optical Property of Dy:CaF2-SrF2 Crystal Fabricated by Multicrucible Temperature Gradient Technology

Dy3+-doped CaF2-SrF2 crystals with various Dy3+ dopant concentrations were synthesized by multicrucible temperature gradient technology (MC-TGT). Dy:CaF2-SrF2 crystals were fluorite structured and crystallized in cubic Fm3¯m space group, as characterized by X-ray diffraction. The crystallographic site concentration was calculated from the measured density by Archimedes’ hydrostatic weighing principle. The optical transmission reached over 90% with a sample thickness of 1.0 mm. The Sellmeier dispersion formula was obtained following the measured refractive index in a mid-IR range of 1.7–11 μm. Absorption coefficients of 6.06 cm−1 and 12.71 cm−1 were obtained at 804 nm and 1094 nm in 15% Dy:CaF2-SrF2 crystal. The fluorescence spectra of 15 at.% Dy:CaF2-SrF2 showed the strongest wavelength peak at 2919 nm with a full width at half maximum (FWHM) of 267 nm under an excitation wavelength of 808 nm. The fluorescence lifetimes were illustrated for different Dy3+ dopant levels of 5%, 10% and 15%. The results indicate that the Dy:CaF2-SrF2 crystal is a promising candidate for compact mid-IR lasers.