Mid-infrared Region Research Articles

Interaction of light with water under clear and algal bloom conditions

Algal blooms are a major problem in water bodies throughout the world. Algal blooms that produce harmful toxins are termed harmful algal blooms (HABs). It is important to monitor water bodies for algal blooms as they can be harmful to humans and animals. Monitoring can also allow management agencies to mitigate the blooms. There are challenges in monitoring water bodies such as time, cost, and remoteness. This study aimed to detect algal blooms with satellite images to enable earlier detection in the future. This can help with earlier warning and advisories that will mitigate negative health effects to humans and animals. Areas with algal blooms behaved like vegetation in certain regions of the electromagnetic spectrum (EMS), while in others it resembled water. As algal blooms became brighter, near-infrared values increased. We also observed a high ratio vegetation index and low mid-infrared values confirm the presence of algae and distinguish them from vegetation. Satellite images can be used to detect algal blooms in water bodies in Wyoming, based on how algae interact with light in the near and mid-infrared regions.

Mid-infrared spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration.

We present the low temperature gas-phase vibrational spectrum of ionised 1-cyanonaphthalene (1-CNN+) in the mid-infrared region. Experimentally, 1-CNN+ ions are cooled below 10 K in a cryogenic ion trapping apparatus, tagged with He atoms and probed with tuneable radiation. Quantum-chemical calculations are carried out at a density functional theory level. The spectrum is dominated by the CN-stretch at 4.516 μm, with weaker CH modes near 3.2 μm.

A short guide to recent developments in laser-based gas phase spectroscopy, applications, and tools

This article provides an overview of laser-based absorption spectroscopy applications and discusses the parameter space and requirements of laser systems for each of these applications, with a special emphasis on frequency comb systems. We walk the reader through the basics of laser absorption spectroscopy, review common line-broadening mechanisms as fundamental challenges to precision spectroscopy, look into established solutions, introduce frequency-comb-based absorption spectroscopy, and suggest a novel approach to broadband precision spectroscopy in the mid-infrared spectral region based on a combination of broadband high-power ultra-stable optical frequency combs, crystalline supermirror technology, and an instrumental line-shape-free measurement technique. We conclude after an introduction of noise sources and their implications for precision measurements with an in-depth discussion and overview of the current state-of-the-art laser and optical parametric frequency conversion technologies.

High-performance mid-infrared refractive index sensing all-dielectric metasurface with dual resonance excited by bound states in the continuum and toroidal dipole mode

Converting bound states in the continuum (BICs) domain to quasi-BICs regime effectively achieves high Q-factor excitation, enabling refractive index sensing. In this paper, we propose an all-dielectric metasurface consisting of four silicon nanopore cylinders. While maintaining a four-fold symmetry, an asymmetric distribution of nanopores is introduced, creating two resonances in the mid-infrared range. Through near-field analysis and multipole decomposition, it is demonstrated that magnetic dipoles (MD) and toroidal dipoles (TD) dominate the resonance modes, and the sensing performance of the structure is investigated. The quality factor (Q) and sensitivity reach 6688 and 1140nm/RIU, respectively. The sensing characteristics in different refractive index (RI) media are analyzed, and the results show that the refractive index sensing capability of the dielectric metasurface is influenced by its structural parameters and exhibits a significant linear response relationship. Furthermore, by varying the structural parameters of the dielectric metasurface, we also discovered the differences in sensing performance within different wavelength ranges. We study all polarization angle robust quasi-BICs in the mid-infrared spectral region, which can provide new references for polarization-insensitive metasurfaces with dual resonances. Polarization-insensitive technology can avoid the need for compensating the polarization state of the light signal in the sensor and improve the performance and reliability of the sensor.

Photoisomerization-induced LMR shift for UV radiation detection

This work presents an optical sensor for ultraviolet radiation (UV) detection, based on the combined effects of Lossy Mode Resonance (LMR) in the mid infrared (MIR) spectral region and the photoisomerization of a polymeric dye coating. LMR was obtained by means of a sputtered SnO2 thin film on a tetrafluoroethylene-perfluoro (or alkoxy Vinyl Ether, PFA) substrate, along with a photo sensitive coating based on poly R-478. Obtained devices shown response and recovery times of 12 and 43 s, respectively, for an UV excitation of 71 mW at 365 nm. Sensitivity as a function of the excitation wavelength was studied with the highest value of 26 nm/mW obtained at 280 nm. For this excitation wavelength, the limit of detection (LoD) obtained was 0.024 mW. Four different excitation wavelengths were used to cover all UV regions (280, 310, 365 and 395 nm). All measurements were performed at room temperature and humidity (25 °C ± 1 °C and 13% R.H. ± 2% R.H. respectively). As far as we know, it is the first time that the LMR effect has been recognized in combination with a photoisomerization process.

Mid-infrared second-harmonic generation and its red-shift signal induced by cross-phase modulation in an AsSe2 soft glass microstructured optical fiber

In this study, we investigate an AsSe2 soft glass microstructured optical fiber (MOF) featuring a hexagonal arrangement of six holes. The MOF is subjected to femtosecond laser pumping, employing a pump wavelength range spanning from 3950 nm to 4100 nm. Our experimental results reveal an intriguing outcome: a tunable mid-infrared second-harmonic generation (SHG) effect is observed, yielding a wavelength range of ∼ 1980 nm to ∼ 2203 nm. The maximum conversion efficiency is achieved at 4100 nm with a power of 130 mW, which can be up to 9.2E-5. The observed SHG is primarily due to the surface nonlinearity polarization at the core-cladding interface. Additionally, we increase the additional degrees of freedom of the SH signal by strong third-order nonlinearity, and demonstrate that strong self-phase modulation (SPM) of pump and cross-phase modulation (XPM) of SH signal help broaden the SH signal by means of generating new wavelength lobes. To the best of our knowledge, this is the first time that strong XPM-based SH signal is observed in an optical fiber in the mid-infrared wavelength region. The realized strong second-order and third-order nonlinearity might expand the fundamental physical mechanism of SHG in optical fiber especially in mid-infrared region, which would have important applications in telecommunications, laser technology, and quantum photonics.

On the use of property-oriented basis sets for the simulation of vibrational chiroptical spectroscopies

We computed vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra for a test set of six chiral compounds using two standard density-functionals and an array of basis sets. We analysed the performance of property-oriented basis sets using a quadruple-zeta basis as a reference against four key metrics. We find little qualitative difference between the spectra produced by the larger basis sets (ORP, LPolX, aug-cc-pVTZ, and aug-cc-pVQZ), though their quantitative metrics exhibit wide variations. The smaller basis sets (rDPS, augD-3-21G, augT3-3-21G, Sadlej-pVTZ, and aug-cc-pVDZ) performed better for VCD rotatory strengths than for the corresponding ROA circular intensity differences (CIDs). However, this trend diminishes as the basis-set size is increased, lending validity to the conclusion that more robust property-oriented basis sets are required for ROA spectral generation than that of VCD. We observed improved performance in the mid-infrared region compared to the high-frequency regime, as well as overestimation of VCD rotatory strengths in the latter region as compared to the reference. We conclude that the ORP and LPol-ds basis sets are the most efficient and effective choices of basis set for the prediction of VCD and ROA spectra, as they provide both highly accurate results at reduced computational expense.

Novel Deposition Method of Crosslinked Polyethylene Thin Film for Low-Refractive-Index Mid-Infrared Optical Coatings.

Mid-infrared optics require optical coatings composed of high- and low-refractive-index dielectric layers for the design of optical mirrors, filters, and anti-reflection coatings. However, there are not many technologies for depositing a material with a refractive index of less than 2 and a low loss in the mid-infrared region. Here, we present a unique deposition method of crosslinked polyethylene thin film for mid-IR optical filter design. Polyethylene has a refractive index of 1.52 in the mid-infrared region and a small number of absorption peaks, so it is useful for making optical filters in the mid-infrared region. Only 1 keV of energy is required to crosslink the entire film by irradiating an electron beam while depositing polyethylene. In addition, crosslinked polyethylene thin film has high mechanical strength, so there is no cracking or peeling when used with germanium. This allows for the use of crosslinked polyethylene as a low refractive index for mid-infrared optical coating.

Growth and efficient laser emission of Er3+ doped LGGG single crystal at 2.8 μm

A novel kind of high-quality Er3+:LGGG crystal has been grown using the Czochralski method and exhibited excellent lasing performance for the first time at around 2818 nm in the mid-infrared spectral region. The J-O intensity parameters, spontaneous emission probability, branching ratio, and exited state lifetimes parameters have been calculated for the first time using the J-O theory, providing theoretical references for future analysis of the absorption and emission characteristics of Er3+:LGGG crystals. The fluorescence lifetimes of the upper (4I11/2) and lower (4I13/2) laser levels are 1.42 and 5.18 ms, respectively. Under 976 nm laser pumping, a continuous-wave laser output of 374 mW with excellent beam quality factors Mx2/My2 of 1.374/1.228 has been achieved by using the Er3+:LGGG crystal. These results indicate that Er3+:LGGG crystals are promising materials for generating 2.8 μm mid-infrared lasers.

Mid-IR supercontinuum generation using a slab with D-shaped/semi-ellipse core waveguide at 4μm

In the present article, we designed a D-shaped optical waveguide for supercontinuum generation. The designed waveguide consists of a slab with a D-shape core (or semi-ellipse) made of As2Se3 which is sandwiched between top and bottom claddings made of GeAsS chalcogenide glass. Pulse confinement, transmission loss, and nonlinear parameters are taken to be in consideration while optimizing the waveguide parameters. In this work, we have numerically calculated the effect of waveguide parameters on dispersion. In addition, we have studied the effect of the D-shaped parameter ‘b’ on the supercontinuum spectrum. For b = 1.9 μm, the proposed waveguide achieves a broad-band supercontinuum spanning from 1.9 μm to 24.5 μm by pumping 50 fs pulse duration sech pulses at the central wavelength of 4 μm, with a peak power of 5 kW. Apart from this, we have also evaluated the supercontinuum spectra with 1 kW, and 2 kW peak powers. The designed waveguide in this paper is easy to fabricate because of its semi-ellipse core shape. From the numerical results, it is pointed out that the proposed waveguide should be useful in the generation of supercontinuum sources, telecommunications, and spectroscopy in the mid-infrared region.

VTe2: Broadband Saturable Absorber for Passively Q-Switched Lasers in the Near- and Mid-Infrared Regions.

In this study, we demonstrate the fabrication of a novel 2D transition metal dichalcogenide, VTe2, into a saturable absorber (SA) by using the liquid phase exfoliation method. Furthermore, the first-principles calculations were conducted to elucidate the electronic band structures and absorption spectrum. The nonlinear optical absorption properties of VTe2 at 1.0, 2.0, and 3.0 μm were measured using open-aperture Z-scan and P-scan methods, which showed saturation intensities and modulation depths of 95.57 GW/cm2 and 9.24%, 3.11 GW/cm2 and 7.26%, and 15.8 MW/cm2 and 17.1%, respectively. Furthermore, in the realm of practical implementation, the achievement of stable passively Q-switched (PQS) lasers employing SA composed of few-layered VTe2 nanosheets has manifested itself with broadband operating wavelengths from 1.0 to ∼3.0 μm. Specifically, PQS laser operations from near-infrared to mid-infrared with pulse durations of 195 and 563 ns for 1.0 and 2.0 μm solid-state lasers, respectively, and 749 ns for an Er3+-doped fluoride fiber laser at 3.0 μm were obtained. Our experimental results demonstrate that VTe2 is a potential broadband SA device for achieving PQS lasers. To the best of our knowledge, this is the first demonstration of using VTe2 as an SA in PQS lasers in the near- and mid-infrared regions, which highlights the potential of VTe2 for future research and applications in optoelectronic devices.

Evaluation of Vicia faba plant genotypes using non-destructive vibrational molecular spectroscopic technique (ATR-FT/IR): molecular structure profiles of protein in relation to nutritional characteristics

This study aimed to evaluate the impact of genotypes and tannin levels on the nutritional characteristics of faba bean seeds and their relation to protein molecular structure profiles using Fourier transform infrared spectroscopy (FTIR). Eight genotypes with low tannin (LT, n = 3) and normal tannin (NT, n = 5) levels were studied. Standard methods of analysis and NRC 2001 were used to obtain chemical and energy parameters. The protein molecular spectral study was performed using a spectrometer JASCO FT/IR–4200. Molecular features were analyzed in the mid-infrared region at ~4000–800 cm−1 and protein-related functional groups were obtained using OMNIC software. Results showed higher ( P < 0.01) soluble crude protein (SCP), rapidly degradable protein fraction (PA2), and intestinal digestibility of bypass protein (dIDP) in LT than NT. The slowly degradable protein fraction (PB2) was higher in NT ( P < 0.01) compared to LT. Higher absorbance was observed in spectral peaks related to amide I, amide II, and β-sheet in NT ( P < 0.05) compared to LT. The area ratio of amide I to amide II and the height ratio of α-helix to β-sheet were higher in LT compared to NT ( P < 0.01). This study provides a better understanding of associations between structure and nutritional characteristics in faba bean genotypes with different tannin levels.

Urban open-air chemical sensing using a mobile quantum cascade laser dual-comb spectrometer

Detection of airborne chemical releases in densely populated urban environments requires precise sensors with high temporal and spatial resolution capable of covering large areas. For this purpose, we present a mobile mid-infrared quantum cascade laser dual-comb spectrometer for identification and quantification of chemical plumes. Field tests with the remote sensor were conducted during daytime in the downtown Boston area over a five day period during which chemical releases were simulated by intermittently emitting non-toxic substances. Open-air sensing was performed with retroreflectors positioned at up to 230 m distance and with sensitivities in the ppm m range for one second of averaging time. The field campaign demonstrates a step toward a semiconductor dual-comb spectroscopic sensor in the mid-infrared fingerprint region, suitable for long-term deployments. These types of sensors will be valuable complements to existing optical sensors for urban hazardous gas leak monitoring, air quality assessments, and localization of clandestine chemical production.

Combined Ionic Membrane and Silica Desiccant Configuration for Maintenance-Free Humidity Control in Equipment

Much scientific equipment requires the use of humidity control technologies. This includes instruments with hygroscopic optics, such as infrared spectrometers, OPOs and some lasers. The most common strategies include nitrogen purging or desiccant bag replacement, which involve maintenance and running costs. In this work we present a dual strategy, combining both ionic membranes and silica desiccant, which results in a reusable and maintenance-free scheme for humidity control. The desiccant action of the silica gels, the membrane, and combinations thereafter, are studied. It is shown that the combination of the silica gel desiccants and the membrane is the most efficient configuration, reducing the humidity from 73% to only 15% in 20 h in a 70 L volume and from 80% to 20% in 40 h in a 230 L volume. An experiment over 5 days showed that the status of the silica gel desiccants that had adsorbed high water vapor levels returned to normal after they were enclosed together with the ionic membrane in the 70 L volume. Finally, measurements taken by a commercial infrared spectrometer of the reduction in the H2O lines absorption in the mid-infrared region under the operation of the combined configuration are examined. It was demonstrated that H2O lines with low to moderate absorption almost disappeared when the humidity levels inside the spectrometer dropped from 42.5% to 15.1% in the span of 90 min, while lines with stronger absorption remained present even though they showed the highest percentage of change.

Mid-Infrared Gas Sensing Based on Electromagnetically Induced Transparency in Coupled Plasmonic Resonators.

The existence of surface plasmon polaritons in doped silicon micro-scale structures has opened up new and innovative possibilities for applications, such as sensing, imaging, and photonics. A CMOS-compatible doped Si plasmonic sensor is proposed and investigated. The plasmon resonance can be tuned by controlling the carrier density and dopant concentration. In this paper, we demonstrate that using silicon doped with phosphorus at a concentration of 5 × 1020 cm-3 can induce surface plasmon resonance in the mid-infrared region. Two ring resonators of two different radii based on metal-insulator-metal waveguide structures are studied individually. Then, the two ring resonators are integrated in the same device. When the two ring resonators are coupled and resonate at the same frequency; two distinct resonance spectral lines are generated with striking features that improve its potential use for sensing and modulation applications. The propagating plasmonic mode is studied, including its mode profile and bend loss. We evaluate the effectiveness of a microstructure gas sensor with dimensions of 15 μm × 15 μm by measuring its sensitivity and selectivity towards methane and ethane gases. Small alterations in the surrounding refractive index led to noticeable shifts in the resonance peak. The sensor achieved a sensitivity of 7539.9 nm/RIU at the mid-infrared spectral range around the 7.7 μm wavelength. Furthermore, by combining the resonators, we can achieve a smaller full width at half maximum (FWHM), which will ultimately result in greater sensitivity than using a single-ring resonator or other plasmonic resonator configurations. Once the sensitivity and selectivity of the sensor are measured, the FOM can be calculated by dividing the sensitivity by the selectivity of the sensor, resulting in an FOM of 6732.

Unraveling the optoelectronic properties of CoSbx intrinsic selective solar absorber towards high-temperature surfaces

The combination of the ability to absorb most of the solar radiation and simultaneously suppress infrared re-radiation allows selective solar absorbers (SSAs) to maximize solar energy to heat conversion, which is critical to several advanced applications. The intrinsic spectral selective materials are rare in nature and only a few demonstrated complete solar absorption. Typically, intrinsic materials exhibit high performances when integrated into complex multilayered solar absorber systems due to their limited spectral selectivity and solar absorption. In this study, we propose CoSbx (2 < x < 3) as a new exceptionally efficient SSA. Here we demonstrate that the low bandgap nature of CoSbx endows broadband solar absorption (0.96) over the solar spectral range and simultaneous low emissivity (0.18) in the mid-infrared region, resulting in a remarkable intrinsic spectral solar selectivity of 5.3. Under 1 sun illumination, the heat concentrates on the surface of the CoSbx thin film, and an impressive temperature of 101.7 °C is reached, demonstrating the highest value among reported intrinsic SSAs. Furthermore, the CoSbx was tested for solar water evaporation achieving an evaporation rate of 1.4 kg m−2 h−1. This study could expand the use of narrow bandgap semiconductors as efficient intrinsic SSAs with high surface temperatures in solar applications.

The deactivation effects of Nd3+ ion for 2.85 μm laser in Ho3+/Nd3+ co-doped fluorotellurite glass

The 2.85 μm band has garnered significant attention for its wide range of applications in the mid-infrared region, and Ho3+ doped fluorotellurite fiber shows great promise as a gain medium for the 2.85 μm fiber laser. To achieve efficient population inversion for Ho3+ ions at 2.85 μm, Ho3+/Nd3+ co-doped fluorotellurite glasses with low hydroxyl were synthesized. The deactivation effect of Nd3+ ions to Ho3+: 5I7 levels was investigated through emission spectra and lifetime decay curves under 890 nm excitation. The results show that Nd3+ ions can effectively quench the Ho3+: 2.05 μm emission and help the Ho3+: 5I6 → 5I7 transition to overcome the bottleneck of particle population inversion. Ultimately, the particle population inversion corresponding to 2.85 μm luminescence was realized in the Ho3+/Nd3+ co-doped fluorotellurite glass, and indicates that a maximum of 1.64 W laser at 2.85 μm with a slope efficiency of 8.72 % can be realized under 890 nm pump by numerical simulations.

The effect of terbium on the optical dispersion and magneto-optical properties of YIG crystals grown by flux-Bridgman method

R3Fe5O12 (RIG) crystals are the key elements for magneto-optical isolators in the near-infrared (NIR) to mid-infrared (MIR) region, with ever-growing demands for integrated photonics. However, the growth of high-quality single crystals is still a big obstacle. The effect of rare earths on the optical and magneto-optical properties of YIG crystals is not well understood. Herein, a series of high quality Tb3+ doped yttrium iron garnet (Y3-xTbxFe5O12, x = 0, 0.5, 1.0, 1.5, 3.0) crystals have been successfully obtained by the flux-Bridgman method, with sizes over 20 mm. Tb:YIG crystals reserve typical cubic garnet structure, with spatial group of Ia3d. The lattice constants increase from 12.377 Å (YIG) to 12.448 Å (TbIG). The refractive index decreases from 2.38 (500 nm) to 2.11 (2500 nm) for YIG crystal, and it reduces from 2.51 (500 nm) to 2.17 (2500 nm) for TbIG crystal. The optical dispersion of the refractive indices was well fitted by the Wemple and DiDomenico (WDD) and the Sellmeier models, respectively. Relatively lower values of the absorption coefficient of the Tb:YIG crystals confirm the high transparency in the NIR region. The characteristic absorption of Tb3+ was observed from 1700 nm to 2500 nm. The specific Faraday rotation angles (θF) of both YIG and TbIG decrease with increasing wavelength, reaching 235.4 and 366.5 °/cm at 1300 nm, respectively. Compared with that of YIG, θF of TbIG crystal shows stronger wavelength dependence. This work provides more insight into the role of rare earths on the optical and magneto-optical behavior of RIG crystals, which will accelerate the design of high-performance magneto-optical crystals for application in NIR-MIR wavelength.

Ultra-wideband chiroptical response by tri-layer anisotropic plasmonic metamaterial

The use of plasmonic chiral metamaterials for the control of circular polarization has the potential to replace conventional optical equipment for polarization-related applications. The ultra-broadband chiroptic response using plasmonic constituents is delivered by elaborate three-dimensional (3D) helical structures, nevertheless, their implementation is complicated, time-consuming, and poses a significant scaling difficulty at the nano level. Ultra-broadband response from planar constituents is particularly necessary as a means to circumvent the challenges of 3D metamaterials. Here we present a planar plasmonic structure composed of tri-layer anisotropic arrays constituting nanowires and cut-wires to generate dual overlapped chiral bands. Based on this tri-layer approach, we numerically realized ultra-broadband planar plasmonic metamaterials to function in the near- and mid-infrared regions with a bandwidth range of 1.38–3.07 µm and 4.00–8.10 µm, and maximum circular dichroism performance of 0.90 and 0.92 respectively. The structures are ultracompact, misalignments tolerant, and can be extended to additional spectral regions through structural engineering. The proposed metamaterial has the potential to be used in the creation of ultra-compact, high-performance devices for a wide variety of uses, such as those in the fields of optical communication, biological diagnosis, high-contrast polarization imaging, high-accuracy polarimetric measurements, and spectroscopy.

Above 10 W, 100 kHz-class cavity-dumped Tm:YAP laser at 1.94 μm

We demonstrate a high-repetition-frequency, cavity-dumped Tm:YAP slab laser, producing short nanosecond pulse at 1.94 μm. A thermal-lens-compensated cavity with a dual-end pumping configuration is developed for high-power operation. The achieved maximum Tm laser power is 10.7 W, with a pulse width of 26.4 ns at a frequency of 110 kHz, resulting in a peak power of 3.68 kW. To the best of our knowledge, this represents the highest output power for the cavity-dumped Tm laser. The results provide a robust scheme to develop high-power, high-repetition-frequency diode-pumped 2 μm lasers with a constant sub-50 ns pulse duration, opening avenues for versatile applications including medical treatment, material processing, and nonlinear frequency conversion towards the mid-infrared region.