Mid-infrared Spectrum Research Articles

Ge-on-Si waveguides for sensing in the molecular fingerprint regime.

Low loss, single mode, Ge-on-Si rib waveguides are used to demonstrated optical sensing in the molecular fingerprint region of the mid-infrared spectrum. Sensing is carried out using two spin-coated films, with strong absorption in the mid-infrared. These films are used to calibrate the modal overlap with an analyte, and therefore experimentally demonstrate the potential for Ge-on-Si waveguides for mid-infrared sensing applications. The results are compared to Fourier transform infrared spectroscopy measurements. The advantage of waveguide spectroscopy is demonstrated in terms of the increased optical interaction, and a new multi-path length approach is demonstrated to improve the dynamic range, which is not possible with conventional FTIR or attenuated total reflection (ATR) measurements. These results highlight the potential for Ge-on-Si as an integrated sensing platform for healthcare, pollution monitoring and defence applications.

Self-Organized Nanorod Arrays for Large-Area Surface-Enhanced Infrared Absorption

Capabilities of highly sensitive surface-enhanced infrared absorption (SEIRA) spectroscopy are demonstrated by exploiting large-area templates (cm2) based on self-organized (SO) nanorod antennas. We engineered highly dense arrays of gold nanorod antennas featuring polarization-sensitive localized plasmon resonances, tunable over a broadband near- and mid-infrared (IR) spectrum, in overlap with the so-called "functional group" window. We demonstrate polarization-sensitive SEIRA activity, homogeneous over macroscopic areas and stable in time, by exploiting prototype self-assembled monolayers of IR-active octadecanthiol (ODT) molecules. The strong coupling between the plasmonic excitation and molecular stretching modes gives rise to characteristic Fano resonances in SEIRA. The SO engineering of the active hotspots in the arrays allows us to achieve signal amplitude improved up to 5.7%. This figure is competitive to the response of lithographic nanoantennas and is stable when the optical excitation spot varies from the micro- to macroscale, thus enabling highly sensitive SEIRA spectroscopy with cost-effective nanosensor devices.

Coherent Mid-IR Supercontinuum Generation using Tapered Chalcogenide Step-Index Optical Fiber: Experiment and modelling

Mid-infrared region of electromagnetic spectrum has increased a lot of scientific and technical interest because of its utility to figure out the molecular fingerprints. Current mid-infrared light sources including quantum cascade lasers, thermal-emitters, and synchrotron radiation are not suitable for various potential applications where we require coherent, portable and broadband light sources. During the current decade, several efforts have been put forwarded to extend the spectral range of the supercontinuum. However, the coherent mid-infrared supercontinuum spectrum in the mid-infrared region has been demonstrated rarely. Here, we demonstrate a coherent mid-infrared supercontinuum using a tapered chalcogenide fiber pumped at various wavelength ranging from 2 µm to 2.6 µm. Experimental observations show that the supercontinuum spectrum extending from ~1.6 µm to 3.7 µm can be achieved using a 3 cm long tapered chalcogenide step-index optical fiber pumped with femtosecond laser pulses at 2.6 µm. To the best of our knowledge, using short pump wavelengths at 2 µm to 2.6 µm in an all-normal dispersion engineered chalcogenide glass fiber, the coherent supercontinuum spectrum has been reported first time. Such coherent broadband light source has its key prominence for the various prospective applications in the fields of bio-medical, sensing, and multiplex coherent anti-Stokes Raman scattering microspectroscopy.

Chinese Spirits Identification Model Based on Mid-infrared Spectrum

Chinese Spirits Identification Model Based on Mid-infrared Spectrum

A direct oriented-attachment growth of lead-chalcogenide mid-infrared nanocrystals film on amorphous substrates

A direct oriented-attachment (OA) growth of lead-chalcogenide nanocrystals (NCs) on amorphous substrates leads to the synthesis of (111) dominated PbSe NCs for the first time. These NCs uniformly assembled on glass slides forming mirror-like thin films of tunable quantum confining effect in the mid-infrared spectrum.

Silicon photonics for telecom and data-com applications

In recent decades, silicon photonics has attracted much attention in telecom and data-com areas. Constituted of high refractive-index contrast waveguides on silicon-on-insulator (SOI), a variety of integrated photonic passive and active devices have been implemented supported by excellent optical properties of silicon in the mid-infrared spectrum. The main advantage of the silicon photonics is the ability to use complementary metal oxide semiconductor (CMOS) process-compatible fabrication technologies, resulting in high-volume production at low cost. On the other hand, explosively growing traffic in the telecom, data center and high-performance computer demands the data flow to have high speed, wide bandwidth, low cost, and high energy-efficiency, as well as the photonics and electronics to be integrated for ultra-fast data transfer in networks. In practical applications, silicon photonics started with optical interconnect transceivers in the data-com first, and has been now extended to innovative applications such as multi-port optical switches in the telecom network node and integrated optical phased arrays (OPAs) in light detection and ranging (LiDAR). This paper overviews the progresses of silicon photonics from four points reflecting the recent advances mentioned above. CMOS-based silicon photonic platform technologies, applications to optical transceiver in the data-com network, applications to multi-port optical switches in the telecom network and applications to OPA in LiDAR system.

基于双芯光子晶体光纤的中红外表面等离子体共振低折射率传感器

基于双芯光子晶体光纤的中红外表面等离子体共振低折射率传感器

Novel Single Hole Exposed-Suspended Core Localized Surface Plasmon Resonance Sensor

Flexibility in design and controlling the wave- guide properties in photonic crystal fiber (PCF) has enabled diverse plasmonic sensing devices with attractive features. Here, we propose a novel single air hole exposed core PCF sensor based on localized surface plasmon resonance (LSPR) for bio-analyte sensing. To supports the LSPR, a gold (Au) nano strip is considered instead of continuous metal film making the proposed sensor cost-effective while experiencing low loss. A thin layer of titanium oxide (TiO2) is also used between the Au and silica glass to assist adhesion, which also contributes to enhancing the sensing performance. Considering the refractive index (RI) variation in the dielectric layer, the sensor performance analysis is carried out via finite element method (FEM) based commercially available software COMSOL Multiphysics in the visible to mid-infrared spectrum. According to numerical results, the proposed sensor shows maximum amplitude sensitivity (AS) of 1449 RIU−1 and a maximum wavelength sensitivity (WS) of 50,000 nm/RIU with a corresponding resolution of $2\times 10^{-6}$ in a wide RI range. Besides, being highly linear in sensing performance, the sensor attains low loss, with an improved figure of merit (FOM). Considering the simple architecture and competitive sensing performance, the proposed sensor could be used effectively in RI sensing applications, especially in bio-sensing.

High-Q surface electromagnetic wave resonance excitation in magnetophotonic crystals for supersensitive detection of weak light absorption in the near-infrared

The mid-infrared spectrum can be recorded from almost any material, making mid-infrared spectroscopy an extremely important and widely used sample characterization and analysis technique. However, sensitive photoconductive detectors operate primarily in the near-infrared (NIR), but not in the mid-infrared, making the NIR more favorable for accurate spectral analysis. Although the absorption cross section of vibrational modes in the NIR is orders of magnitude smaller compared to the fundamental vibrations in the mid-infrared, different concepts have been proposed to increase the detectability of weak molecular transitions overtones. Yet, the contribution of magnetophotonic structures in the NIR absorption effect has never been explored so far. Here we propose high-Q magnetophotonic structures for a supersensitive detection of weak absorption resonances in the NIR. We analyze the contributions of both magnetic and nonmagnetic photonic crystal configurations to the detection of weak molecular transitions overtones. Our results constitute an important step towards the development of highly sensitive spectroscopic tools based on high-Q magnetophotonic sensors.

Circumstellar CO J = 3→2 detected around the evolving metal-poor ([Fe/H] ≈ −1.15 dex) AGB star RU Vulpeculae

ABSTRACT We report the first detection of CO J = 3→2 around a truly metal-poor evolved star. RU Vulpeculae is modelled to have Teff ≈ 3620 K, L ≈ 3128 ± 516 L⊙, log(g) = 0.0 ± 0.2 dex and [Fe/H] = −1.3 to −1.0 dex, and is modelled to have recently undergone a thermal pulse. Its infrared flux has approximately doubled over 35 yr. ALMA observations show the 3→2 line is narrow (half-width ∼1.8–3.5 km s−1). The 2→1 line is much weaker: it is not confidently detected. Spectral-energy-distribution fitting indicates very little circumstellar absorption, despite its substantial mid-infrared emission. A VISIR mid-infrared spectrum shows features typical of previously observed metal-poor stars, dominated by a substantial infrared excess but with weak silicate and (possibly) Al2O3 emission. A lack of resolved emission, combined with weak 2→1 emission, indicates the dense circumstellar material is truncated at large radii. We suggest that rapid dust condensation is occurring, but with an aspherical geometry (e.g. a disc or clumps) that does not obscure the star. We compare with T UMi, a similar star which is currently losing its dust.

Unidentified infrared emission features in mid-infrared spectrum of comet 21P/Giacobini-Zinner

Comet 21P/Giacobini-Zinner (hereafter, comet 21P/G-Z) is a Jupiter-family comet and a parent comet of the October Draconids meteor shower. If meteoroids originating from a Jupiter-family comet contain complex organic molecules, such as amino acids, they are essential pieces of the puzzle regarding the origin of life on Earth. We observed comet 21P/G-Z in the mid-infrared wavelength region using the Cooled Mid-infrared Camera and Spectrometer (COMICS) on the 8.2 m Subaru Telescope on UT 2005 July 5. Here, we report the unidentified infrared (UIR) emission features of comet 21P/G-Z, which are likely due to complex organic molecules (both aliphatic and aromatic hydrocarbons), and the thermal emission from amorphous/crystalline silicates and amorphous carbon grains in its mid-infrared low-resolution spectrum. The UIR features at ~8.2 μm, ~8.5 μm, and ~11.2 μm found in the spectrum of comet 21P/G-Z could be attributed to polycyclic aromatic hydrocarbons (or hydrogenated amorphous carbons) contaminated by N- or O-atoms, although part of the feature at ~11.2 μm comes from crystalline olivine. The other feature at ~9.2 μm might originate from aliphatic hydrocarbons. Comet 21P/G-Z is enriched in complex organic molecules. Considering that the derived mass fraction of crystalline silicates in comet 21P/G-Z is typical of comets, we propose that the comet originated from a circumplanetary disk of giant planets (similar to Jupiter and Saturn) where was warmer than the typical comet-forming region (5–30 au from the Sun) and was suitable for the formation of complex organic molecules. Comets from circumplanetary disks might be enriched in complex organic molecules, such as comet 21P/G-Z, and may have provided pre-biotic molecules to ancient Earth by direct impact or meteor showers.

Fabrication of Soft-Glass-Based Wire Array Metamaterial Fibers for Applications at Infrared Frequencies

Metamaterials for the mid-infrared spectrum require subwavelength meta-structures with dimensions of a few hundreds of nanometers. Fabrication via fiber drawing is challenging as the Plateau–Rayleigh instability caused by interfacial surface tension between the liquid metal and the dielectric during the drawing leads to fluctuation of the structure, preventing drawing of uniform wire array structures with such dimensions. Here, conventional fiber drawing technique is employed in the fabrication of wire array metamaterial fibers containing tin wires embedded in soda–lime glass. Plateau–Rayleigh instabilities ensuing detrimental deformations on submicron metallic structures are minimized through the selection of materials with favorable rheological properties and the optimization of the drawing parameters. Uniform wire array structures with wire diameter and spacing as small as 143 and 286 nm, respectively, are demonstrated. The application of this established fabrication process represents a large-volume and low-cost alternative for the production of hyperbolic metamaterials. The new metamaterial fibers achieved open up a range of exciting applications at mid-infrared frequencies, such as lifetime engineering and super-resolution imaging.

Prediction of Milk Coagulation Properties and Individual Cheese Yield in Sheep Using Partial Least Squares Regression

Simple SummaryConsidered that all sheep milk in Italy is destined for cheese processing, traits describing rennet coagulation aptitude should be among the most important selection goals for dairy breeds. To reduce the costs and logistics related to the large-scale recording of these traits, mid-infrared (MIR) spectroscopy could be conveniently used to generate reliable predictions without any additional cost. The aims of this research were to predict the milk coagulation properties (MCP) and individual cheese yield (ILCY) in sheep by MIR spectrometry using partial least squares regression (PLS), and to compare different data pre-treatment procedures. The prediction results observed in the present study, although moderate, suggest the possibility of adding novel phenotypes (e.g., MCP and ILCY) in breeding schemes for dairy sheep breeds. Mid-infrared spectroscopy coupled with PLS regression could allow the prediction of phenotypes at the population level without additional costs.The objectives of this study were (i) the prediction of sheep milk coagulation properties (MCP) and individual laboratory cheese yield (ILCY) from mid-infrared (MIR) spectra by using partial least squares (PLS) regression, and (ii) the comparison of different data pre-treatments on prediction accuracy. Individual milk samples of 970 Sarda breed ewes were analyzed for rennet coagulation time (RCT), curd-firming time (k20), and curd firmness (a30) using the Formagraph instrument; ILCY was measured by micro-manufacturing assays. An Furier-transform Infrared (FTIR) milk-analyzer was used for the estimation of the milk gross composition and the recording of MIR spectrum. The dataset (n = 859, after the exclusion of 111 noncoagulating samples) was divided into two sub-datasets: the data of 700 ewes were used to estimate prediction model parameters, and the data of 159 ewes were used to validate the model. Four prediction scenarios were compared in the validation, differing for the use of whole or reduced MIR spectrum and the use of raw or corrected data (locally weighted scatterplot smoothing). PLS prediction statistics were moderate. The use of the reduced MIR spectrum yielded the best results for the considered traits, whereas the data correction improved the prediction ability only when the whole MIR spectrum was used. In conclusion, PLS achieves good accuracy of prediction, in particular for ILCY and RCT, and it may enable increasing the number of traits to be included in breeding programs for dairy sheep without additional costs and logistics.

Mid-infrared laser absorption spectroscopy of the Ne-NO(X2Π) complex.

The rovibrational spectrum of the Ne-NO(X2Π) open-shell complex has been measured in the 5.3 µm region using distributed feed-back quantum cascade lasers to probe the direct absorption in a slit-jet supersonic expansion. Three P-subbands (P' ← P″: 1/2 ← 1/2, 3/2 ← 1/2, and 5/2 ← 3/2) were observed, where P is the projection of the angular momentum J along the inertial a-axis of the complex. The hyperfine structure due to the nuclei spin of 14N (I = 1) was partially resolved in the P' ← P″: 1/2 ← 1/2 and 3/2 ← 1/2 subbands. The observed mid-infrared spectrum of Ne-NO (X2Π) together with the previously reported microwave spectrum was analyzed using a modified semirigid asymmetric rotor Hamiltonian for a planar open-shell complex. The band origin is located at 1876.0606(97) cm-1, which is blue-shifted from that of the NO monomer by only 0.0888 cm-1. The complex shows strong structural relaxation upon excitation of the overall rotation and the internal rotation of the NO subunit.

Photoinduced Dynamics of a Diazidocobalt(III) Complex Studied by Femtosecond UV-Pump/IR-to-Vis-Probe Spectroscopy.

The photochemistry of the cationic diazidocobalt(III) complex, trans-[Co(cyclam)(N3)2]+, following its ligand-to-metal charge transfer (LMCT) excitation is studied in liquid dimethyl sulfoxide (DMSO) solution using femtosecond spectroscopy with detection in a very broad spectral region covering the near-ultraviolet (near-UV) all the way to the mid-infrared (MIR), thereby enabling a combined probing of electronic and vibrational degrees of freedom of the dynamically evolving system. The initially prepared singlet LMCT-state decays, via the metal-centered singlet excited state, 1MC(1Eg), into the triplet ground state, 3MC (3Eg/3A1g), on a time scale shorter than 25 ps. During this time period, the vibrational spectrum demonstrates uniquely that the nature of the complex changes from a monoazidocobalt(II) species bearing a neutral azide radical ligand immediately after photon absorption to a metal-centered open-shell diazidocobalt(III) species. At the same time, the 3MC state is characterized by a very strong absorption band centered at 710 nm, which can be assigned to a transition to the triplet LMCT state. The 1LMCT lifetime is about 2 ps, whereas that of the excited state, 1MC, is defined by the primary intersystem crossing time of 6 ps. The ensuing intersystem recrossing from 3MC to the parent's singlet ground state, 1A1g, occurs with a rate of 1/(110 ps). The mid-infrared pump-probe spectrum after 1 ns, gives evidence for a heterolytic Co-N bond fission with a quantum yield of ∼5%, leading to free azide anions and the monoazido species, trans-[Co(cyclam)(N3)(OSMe2)]+, featuring an oxygen-bound DMSO ligand in its coordination sphere.

A young and obscured AGN embedded in the giant radio galaxy Mrk 1498

Abstract Mrk 1498 is part of a sample of galaxies with extended emission line regions (extended outwards up to a distance of ∼7 kpc) suggested to be photo-ionized by an AGN that has faded away or that is still active but heavily absorbed. Interestingly, the nucleus of Mrk 1498 is at the center of two giant radio lobes with a projected linear size of 1.1 Mpc. Our multi-wavelength analysis reveals a complex nuclear structure, with a young radio source (Giga-hertz Peaked Spectrum) surrounded by a strong X-ray nuclear absorption, a mid-infrared spectrum that is dominated by the torus emission, plus a circum-nuclear extended emission in the [OIII] image (with radius of ∼ 1 kpc), most likely related to the ionization of the AGN, aligned with the small and large scale radio jet and extended also at X-rays. In addition a large-scale extended emission (up to ∼ 10 kpc) is only visible in [OIII]. These data show conclusive evidence of a heavily absorbed nucleus and has recently restarted its nuclear activity. To explain its complexity, we propose that Mrk 1498 is the result of a merging event or secular processes, such as a minor interaction, that has triggered the nuclear activity and produced tidal streams. The large-scale extended emission that gives place to the actual morphology could either be explained by star formation or outflowing material from the AGN.

Mid-Infrared Amplified Spontaneous Emission from the f′ 0g+ (1D2) Ion-Pair State and Spectroscopic Characterization of the Shallow 0g+ (ab) Valence State of I2

In this paper, we describe amplified spontaneous emission (ASE) from the f' 0g+ (1D2) ion-pair state of I2 populated through a two-step laser excitation technique via the B 3Π(0u+) valence state. The intense infrared emission propagating in the direction of the incident laser beam is assigned to the ASE transition from the f' 0g+ (1D2) state to the F' 0u+ (1D2) ion-pair state. The subsequent ultraviolet fluorescence transition from the F' 0u+ (1D2) state to the 0g+ (bb) state as well as the 0g+ (ab) state is also reported. By Franck-Condon simulation of the cascading F' 0u+ (1D2) → 0g+ (bb) band, we determine the population distributions in the F' 0u+ (1D2) state generated by ASE, which are consistent with the intensity profile of the mid-infrared ASE spectrum. Finally, employing these vibrational distributions for the F' 0u+ (1D2) state, spectral parameters for the shallow 0g+ (ab) state are derived.

Octave-spanning single-cycle middle-infrared generation through optical parametric amplification in LiGaS2.

We report the generation of extremely broadband and inherently phase-locked mid-infrared pulses covering the 5 to 11 µm region. The concept is based on two stages of optical parametric amplification starting from a 270-fs Yb:KGW laser source. A continuum seeded, second harmonic pumped pre-amplifier in β-BaB2O4 (BBO) produces tailored broadband near-infrared pulses that are subsequently mixed with the fundamental pump pulses in LiGaS2 (LGS) for mid-infrared generation and amplification. The pulse bandwidth and chirp is managed entirely by selected optical filters and bulk material. We find an overall quantum efficiency of 1% and a mid-infrared spectrum smoothly covering 5-11 µm with a pulse energy of 220 nJ at 50 kHz repetition rate. Electro-optic sampling with 12-fs long white-light pulses directly from self-compression in a YAG crystal reveals near-single-cycle mid-infrared pulses (32 fs) with passively stable carrier-envelope phase. Such pulses will be ideal for producing attosecond electron pulses or for advancing molecular fingerprint spectroscopy.

Contribution of milk mid-infrared spectrum to improve the accuracy of test-day body weight predicted from stage, lactation number, month of test and milk yield

A regular and repeated recording of body weight (BW) is useful information for herd management. BW can be predicted regularly from animal characteristics such as age, lactation number, or lactation stage. Those traits are unfortunately animal unspecific. Adding animal specific information, which can be easily obtained on a large scale, to the BW prediction would be of utmost importance. There are good scientific reasons to suspect links between BW and animal specific characteristics, available in a repeated fashion, such as milk yield and milk composition. This study aimed to demonstrate the feasibility of predicting test-day BW from stage, lactation number, month of test, milk yield and mid-infrared spectra, representing milk composition. Five models were tested initially from 721 BW records collected in 6 herds: day in milk + number of lactation (equation 1a); equation1a + milk yield (equation 1b); only spectral data (equation 1c); equation 1c + equation 1a (equation 2); equation 2 + milk yield (equation 3). Then 3 other equations included the same explicative variables, except that the spectral data were regressed using second order Legendre Polynomials (PL) to take into account changes of spectral data within lactation. Equation 1a and 1b were built using linear regressions and equation 1c until 3 were built using partial least square regressions. These 3 last equations had a higher number of factors. Adding of MIR data in the equation increased of 7% the values of cross-validation R² (R²cv). Potential BW outliers were discarded using a residual analysis based on equation 3. From 662 records, the following statistical parameters were obtained: the calibration coefficient of determination (R²c) = 0.65, R²cv = 0.61, calibration root mean squared error of prediction (RMSEP)=38 kg, and RMSEPcv=40 kg. Low variation of R²c and RMSEPc values obtained from the herd validation confirmed the herd independence of predictions. However, large variability was observed for RMSEPv (37 to 64 kg) suggesting the need to increase the dataset in order to improve the robustness of the equation. By applying the equations on a large spectral database, it was confirmed that the addition of MIR data allows to better model the BW evolution within lactation. Based on these preliminary results, and if a larger validation confirms these findings, this approach could be used to develop equations that are better able to assess BW throughout lactation(s), BW being an important element for management and selection tools.

Far infrared spectroscopy and other spectral and thermal properties of [Li@C60]PF6

The endohedral fullerene [Li@C60]+PF6− was characterized by differential scanning calorimetry (DSC), by electronic absorption spectroscopy in the spectral range from 195 to 800 nm and by FT-IR and far-infrared spectroscopy. [Li@C60]+PF6− shows a sharp melting point with the onset at 86 °C and peak at 90 °C and melting enthalpy of 9.5 kJ/mol. The electronic absorption spectrum of [Li@C60]+PF6− in the UV shows both a hypsochromic shift and a hyperchromic effect with respect to the corresponding electronic transitions of C60. In the mid-infrared spectrum [Li@C60]+ cation displays the typical four band pattern of C60, with small shifts. The far-infrared spectroscopy appears to be the most effective diagnostic tool to distinguish between C60 and endohedral fullerenes like [Li@C60]+. In fact, while C60 does not show any far-infrared vibration, [Li@C60]+PF6− shows four far-infrared bands. Also in an astrochemical perspective the search of endohedral fullerenes must rely mainly on the far-infrared spectral region.