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Black phosphorus (bP) is a promising material for mid-infrared (mid-IR) optoelectronic applications, exhibiting high performance light emission and detection. Alloying bP with arsenic extends its operation toward longer wavelengths from 3.7 μm (bP) to 5 μm (bP3As7), which is of great practical interest. Quantitative optical characterizations are performed to establish black phosphorus-arsenic (bPAs) alloys optoelectronic quality. Anisotropic optical constants (refractive index, extinction coefficient, and absorption coefficient) of bPAs alloys from near-infrared to mid-IR (0.2-0.9 eV) are extracted with reflection measurements, which helps optical device design. Quantitative photoluminescence (PL) of bPAs alloys with different As concentrations are measured from room temperature to 77 K. PL quantum yield measurements reveal a 2 orders of magnitude decrease in radiative efficiency with increasing As concentration. An optical cavity is designed for bP3As7, which allows for up to an order of magnitude enhancement in the quantum yield due to the Purcell effect. Our comprehensive optical characterization provides the foundation for high performance mid-IR optical device design using bPAs alloys.

Y 2 O 3 -MgO composites are promising for mid-infrared windows and domes in harsh environments. However, the insufficient transmittance range (the transmittance >30 % only in ∼2–7 μm) and strong absorption peak (the transmittance <32 % at 7.0 μm) of Y 2 O 3 -MgO composites severely limit their application range because of agglomerations and carbon contamination from organics in the raw materials, currently. In this study, utilizing carbon-free raw materials and high molecular motions, the reduction of carbon contamination and agglomerations within the as-synthesized nanopowers was achieved via the modified co-precipitation synthesis. A highly mid-infrared transparent (the maximum transmittance of 79 % at 6.0 μm) Y 2 O 3 -MgO composite with wide transmittance range (the transmittance >30 % in 2.2–9.7 μm) and weak absorption peaks (the transmittance ≈68.57 % at 7.0 μm) was fabricated by the hot-pressing sintering method using the as-obtained nanopowders in the absence of exogenous dopants. And the modified co-precipitation synthesis is a method with great potential for the development of mid-infrared transparent Y 2 O 3 -MgO composites with wide transmittance range and weak absorption peaks. [ABSTRACT FROM AUTHOR]

Transparent Er-doped Y 2 O 3 ceramics were fabricated using the spark plasma sintering (SPS) technique without any sintering additives to achieve fine-grained mid-infrared laser ceramics. The average grain size of ceramics was typically 300 nm and their in-line optical transmittance in the 2.7 μm mid-infrared range reached approximately 99 % of the theoretical value. The fluorescence spectra and lifetimes confirmed that the ceramics fabricated using SPS exhibited emission characteristics nearly identical to those fabricated using other sintering techniques. Despite the numerous pores in the ceramics and considerably reduced transmittance at an excitation wavelength of 976 nm (approximately 90 % of the theoretical value), a successful laser oscillation at 2.7 μm in the mid-infrared region was achieved. To the best of our knowledge, this is the first report on mid-infrared laser operation for fine-grained ceramics having grain sizes below 500 nm. We believe that this study will contribute to further improvements in the optical properties and development of fine-grained transparent ceramics as new laser materials, particularly non-cubic materials. [ABSTRACT FROM AUTHOR]

Mid-infrared (MIR) Kerr microcombs are of significant interest for portable dual-comb spectroscopy and precision molecular sensing due to strong molecular vibrational absorption in the MIR band. However, achieving a compact, octave-spanning MIR Kerr microcomb remains a challenge due to the lack of suitable MIR photonic materials for the core and cladding of integrated devices and appropriate MIR continuous-wave (CW) pump lasers. Here, we propose a novel slot concentric dual-ring (SCDR) microresonator based on an integrated chalcogenide glass chip, which offers excellent transmission performance and flexible dispersion engineering in the MIR band. This device achieves both phase-matching and group velocity matching in two separated anomalous dispersion regions, enabling phase-locked, two-color solitons in the MIR region with a commercial 2-μm CW laser as the pump source. Moreover, the spectral locking of the two-color soliton enhances pump wavelength selectivity, providing precise control over soliton dynamics. By leveraging the dispersion characteristics of the SCDR microresonator, we have demonstrated a multi-octave-spanning, two-color soliton microcomb, covering a spectral range from 1156.07 to 5054.95 nm (200 THz) at a −40 dB level, highlighting the versatility and broad applicability of our approach. And the proposed multi-octave MIR frequency comb is relevant for applications such as dual-comb spectroscopy and trace-gas sensing. [ABSTRACT FROM AUTHOR]

Interband Cascade Lasers (ICL) have matured into a versatile technological platform in the mid‐infrared spectral domain. To broaden their applicability even further, ongoing research pursues the emission of ultrashort pulses. The most promising approach is passive mode‐locking with a fast saturable absorber. However, despite vast attempts no passive mode‐locked ICL has been demonstrated up to date. In this study, pump‐probe measurements are conducted on the ICL gain, demonstrating that ≈$\approx$60–70% of its dynamic behavior is characterized by a rapid recovery time of 2 ps. The findings explain why passive mode‐locking of ICLs has not succeeded so far, shedding a new light on ICL dynamics as strategies are proposed to overcome the current limitations. [ABSTRACT FROM AUTHOR]

A chalcogenide (ChG) multi‐slot waveguide gas sensor with ChG as the core layer and silicon dioxide (SiO2) as the under‐cladding layer is proposed. Multi‐slot waveguide can be used in the mid‐infrared gas measurement. The optimized power confinement factor (PCF) of the ChG multi‐slot waveguide can be up to 41.3%, which is ∼20% higher than that of the optimized single‐slot waveguide. At the absorption line located at 3.291 μm for methane (CH4) measurement, the limits of detection (LoD) of single‐slot, double‐slot, triple‐slot, quadruple‐slot waveguide sensors are determined to be 68.9, 57.4, 52, 48.6 parts per million (ppm), respectively. Compared with other waveguide sensors in the mid‐infrared, the PCF of the proposed multi‐slot ChG/SiO2 waveguide sensor is enhanced by five times, which has the potential for highly sensitive gas sensing. [ABSTRACT FROM AUTHOR]

Lithium niobate (LN) crystal with anti‐reflective subwavelength structures (ASSs) has great applications in high‐power tunable optical parametric oscillator (OPO) lasers. However, it is still a great challenge to 3D nanofabrication of LN ASSs. Herein, a wet‐etching‐assisted laser polarization domain inversion (WE‐LPDI) technology is proposed to fabricate periodic cone arrays with a period from 200 nm to 4 µm on LN. Based on the optimized structural parameters, large‐area LN ASSs with a period of 1.3 µm and a height of 1.7 µm were fabricated on LN, which exhibits an average transmittance of 3–5 µm increasing from 78% to 85% and a highest transmittance of 88% at 5 µm. It has been demonstrated that the LN ASSs show high stability under high‐temperature and high‐power laser irradiation, which shows potential applications for high‐power mid‐IR lasers. The results indicate that the WE‐LPDI technology provides a novel way for 3D nanofabrication of LN. [ABSTRACT FROM AUTHOR]

The advantage of employing mid-infrared spectrometry for milk analysis in breeding lies in its ability to quickly generate millions of records. However, these records may be biased if the calibration process does not account for their spectral variability when constructing the predictive model. Therefore, this study introduces a novel method for developing a world representative spectral database (WRSD) to reduce the risks of spectral extrapolation when predicting dairy traits in new samples. Using a 2-phase selection procedure that is both efficient and minimizes memory usage, we first generate a decomposition matrix via principal component analysis (PCA) on a dataset of 2,324,443 records. The next phase iterates spectral selection based on a location index from PCA scores, calculating spectra occurrence frequency for refined barycenter estimations. The chosen spectra's barycenter closely aligns with the entire dataset, proving the efficacy of using just 3 principal components. Applied to 4 varied datasets totaling over 21 million records, we select 583,440 spectra to represent spectral diversity, with selection rates between 2.00% and 14.88%. This selection illustrates the spectral variability across different dairy populations and data providers. Demonstrated through a hypothetical calibration set of 71 samples, the WRSD's utility for algorithm developers becomes apparent. This calibration set covers between 91.42% and 98.50% of the WRSD variability, except for the Irish dataset (3.50%), indicating a need for additional samples to accurately represent Irish variability and minimize spectral extrapolation. This study offers valuable insights into the representativeness of training sets for capturing spectral variability within targeted dairy populations. Although the current WRSD does not fully encompass global milk spectral diversity, its development underscores the importance of gathering more data and standardizing spectral information across spectrometer brands. Ultimately, the WRSD proves crucial not just for trait prediction but also for identifying abnormal milk samples, also marking a significant relevance in dairy science technology. The list of standard abbreviations for JDS is available at adsa.org/jds-abbreviations-24. Nonstandard abbreviations are available in the Notes. [ABSTRACT FROM AUTHOR]

A compact and responsive thermoelectric photodetector is introduced for the mid‐infrared. By resonantly coupling mid‐infrared light to a Sb2Te3‐Bi2Te3 thermoelectric junction, a thermocouple is formed that is directly heated by narrow‐band mid‐infrared radiation. Near‐perfect absorption is achieved at this hot junction through the resonantly enhanced coupling of light to free‐electrons in the Bi2Te3 and Sb2Te3 materials. The fabricated devices operate at 3.6 µm and demonstrate a responsivity of 10.2 V W−1, a specific detectivity of 4.6 × 106 cm Hz1/2 W−1, and a bandwidth in the order of 1 kHz. The optimal detection wavelength can be spectrally tuned by changing the resonant cavity dimensions. This work shows a path toward miniaturized mid‐infrared detectors and spectrometers with high sensitivity, responsivity, and bandwidth. Importantly, the device presented here is ideal for industrial production, which it is hoped will provide wider access to mid‐infrared technologies for chemical sensing, medicine, and security. [ABSTRACT FROM AUTHOR]

Gradient refractive index (GRIN) lenses have been widely used for many applications. However, the traditional manufacturing methods of GRIN lenses are very time-consuming and only suitable for macro-scale operations. In addition, those methods do not have the ability to produce other GRIN optical components with complex refractive index profiles like aspheric or freeform components. We report here an approach to produce GRIN micro-optical components in chalcogenide glass based on a direct laser writing technique. Using this approach, we are able to locally modulate the refractive index of the glass subtrates and create an arbitrary refractive index profile. To prove the flexibility of the method for the production of GRIN micro-optics, we fabricated GRIN micro-lenses and a micro-Fresnel axicon (Fraxicon). The optical properties of micro-lenses can be controlled by varying the writing parameters or the substrate thickness. As a result, the working distance of the micro-lenses can extend from 0 to more than 1000 μ m. Also, the micro-Fraxicon exhibits the ability to convert a Gaussian beam to a Bessel-like beam which concentrates the mid-infrared light into an approximately 1200 μ m long confinement zone. [ABSTRACT FROM AUTHOR]

Going through three important iterations, semiconductor material systems have been widely used in important fields such as microelectronics, communications, artificial intelligence, and carbon neutrality. With the rapid development of technologies, the research on a new generation of high-performance semiconductor materials and devices has become the focus of international advanced technology. As one of the most promising fourth-generation semiconductor material, antimonide semiconductor materials have unique advantages and broad application prospects in developing next-generation high-performance, small-volume, low-power, and low-cost infrared optoelectronic devices. In this paper, the development process and research status of antimonide semiconductor lasers at home and abroad were reviewed, the key issues such as design of device structure, material epitaxial growth, mode selection and wavelength expansion were analyzed, high-performance antimonide quantum well lasers have been grown by molecular beam epitaxy technology. The design scheme and key technology for realizing high-power, single-mode and high-beam quality antimonide lasers were emphasized, and the research prospect of single-mode antimonide lasers with excellent characteristics such as low cost, high yield and high power was predicted. [ABSTRACT FROM AUTHOR]

Silicon‐based on‐chip broadband surface‐enhanced infrared absorption (SEIRA) is highly desired for integrated micromolecular detection systems, taking advantages of CMOS mass production, low cost, high sensitivity, etc. However, the silicon platform is difficult to operate in the mid‐infrared wavelength region above 4 µm where abundant fingerprint characteristics of biomolecules are located, because of the strong absorptions in silicon dioxide cladding above 4 µm. Here, a large‐core rib silicon waveguide‐integrated gradient nanoantenna array is proposed for broadband long‐wave infrared biomolecular detection. It is shown that Low loss propagation of light in the long‐wave infrared region up to 7 µm (1428 cm−1) in silicon photonics can be achieved while avoiding complex fabrication techniques. A gradient nanoantenna array is designed on the waveguide to achieve broadband enhancement from 5 to 7 µm (1428–2000 cm−1). Laser spectroscopy of bovine serum albumin on the chip is demonstrated, showing enhancement of absorbance by approximately ten times over laser transmission spectroscopy in the amide bands. Such a platform opens up a new horizon of silicon‐based on‐chip SEIRA biomolecular detection. [ABSTRACT FROM AUTHOR]

In this work, a gas sensing system based on chalcogenide (ChG) glass platform in the mid-infrared (Mid-IR) region is modeled. The proposed gas sensing system composed of a linear tapers waveguide, ridge waveguide, a multimode interferometer (MMI) coupler and transducer arms. The components of the sensing system were simulated using FimmWave from Photon design. First, we determined the structural key parameters of the ridge waveguide that allow for single-mode propagation while maximizing the evanescent confinement field factor. The obtained results show that at the gas absorption wavelengths, λ CO 2 = 4.26 µm and λ CO = 4.6 µm, the evanescent confinement field factor, reached 3.12% and 3.24%, respectively. For these operating wavelengths, a maximum transmission of 99.8% was achieved with a taper length of 450 µm. The footprint of the MMI coupler is 32 × 9975 µm2. A Contrast of 16.6 dB and insertion losses of 2 dB and 2.87 dB were obtained at λ CO 2 = 4.26 µm and λ CO = 4.6 µm respectively. The sensor performance was validated at 4.26 µm and 4.6 µm, respectively, giving a detection limit of 10.73 ppm for carbon dioxide (CO2) at 4.26 µm and 138 ppm for carbon monoxide (CO) at 4.6 µm. A sensitivity of 3.02 mW.L/mol and 0.12 mW. L/mol, was achieved at the wavelenghts of interset. The obtained results of the sensor by the optimizations of its components serve to enhance a gas sensing system based on chalcogenide (ChG) glass platform. [ABSTRACT FROM AUTHOR]

Fiber combiner is an effective device to enhance the power level or broaden the spectral wavelengths through a single monolithic output aperture, by fusing multiple fibers together. This is particularly important in mid‐infrared (MIR) 2–5 µm range, in which the output power of a single laser is limited. Due to the high MIR transmission, chalcogenide glass is an ideal host for constructing MIR fiber combiner. In this study, we report the design, fabrication, and characterization of a homemade 3 × 1 chalcogenide glass fiber combiner. The fiber combiner includes a 3 × 1 As–S input fiber bundle and an output fiber. The input fiber bundle was made by tapering three As–S multimode fibers with a core diameter of 200 µm and a cladding diameter of 250 µm. The taper reduction ratio R was 2, and the length of the taper transition region was ∼2 cm. The output fiber with core diameter of 360 µm and cladding diameter of 570 µm was then spliced with the tapered end of the fiber bundle. The total length of the combiner was ∼53 cm. The measurement of power combination at 4.56 µm indicated that the transmission efficiency of three ports reached 80%, whereas the power combining efficiency of the combiner was measured to be ∼48%. In addition, efficient wavelength combining over one octave has been demonstrated, by launching three different lasers at 2.1, 3.39, and 4.56 µm through the 3 × 1 combiner. It proves that chalcogenide fiber combiner is promising for the applications of high‐level power combination and broadband wavelength combining in MIR 2–5 µm range. [ABSTRACT FROM AUTHOR]

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This study focused on designing an ultra-wideband metamaterial absorber, consisting of layers of Mn (manganese) and MoO3 (molybdenum trioxide) arranged in a planar interleaving pattern, with a matrix square-shaped Ti (titanium) on the top MoO3 layer. Key features of this research included the novel use of Mn and MoO3 in a planar interleaving configuration for designing an ultra-wideband absorber, which was rarely explored in previous studies. MoO3 thin film served as the fundamental material, leveraging its favorable optical properties and absorption capabilities in the infrared spectrum. Alternating layers of Mn and MoO3 were adjusted in thickness and order to optimize absorptivity across desired wavelength ranges. Another feature is that the Mn and MoO3 materials in the investigated absorber had a planar structure, which simplified the manufacturing of the absorber. Furthermore, the topmost layer of square-shaped Ti was strategically placed to enhance the absorber's bandwidth and efficiency. When the investigated absorber lacked a Ti layer, its absorptivity and bandwidth significantly decreased. This structural design leveraged the optical properties of Mn, MoO3, and Ti to significantly expand the absorption range across an ultra-wideband spectrum. When the Ti height was 280 nm, the investigated absorber exhibited a bandwidth with absorptivity greater than 0.9, spanning from the near-infrared (0.80 μm) to the mid-infrared (9.07 μm). The average absorptivity in this range was 0.950 with a maximum absorptivity of 0.989. Additionally, three absorption peaks were observed at 1010, 2510, and 6580 nm. This broad absorption capability makes it suitable for a variety of optical applications, ranging from near-infrared to mid-infrared wavelengths, including thermal imaging and optical sensing. [ABSTRACT FROM AUTHOR]

Abstract Mid-infrared (MIR) Kerr microcombs are of significant interest for portable dual-comb spectroscopy and precision molecular sensing due to strong molecular vibrational absorption in the MIR band. However, achieving a compact, octave-spanning MIR Kerr microcomb remains a challenge due to the lack of suitable MIR photonic materials for the core and cladding of integrated devices and appropriate MIR continuous-wave (CW) pump lasers. Here, we propose a novel slot concentric dual-ring (SCDR) microresonator based on an integrated chalcogenide glass chip, which offers excellent transmission performance and flexible dispersion engineering in the MIR band. This device achieves both phase-matching and group velocity matching in two separated anomalous dispersion regions, enabling phase-locked, two-color solitons in the MIR region with a commercial 2-μm CW laser as the pump source. Moreover, the spectral locking of the two-color soliton enhances pump wavelength selectivity, providing precise control over soliton dynamics. By leveraging the dispersion characteristics of the SCDR microresonator, we have demonstrated a multi-octave-spanning, two-color soliton microcomb, covering a spectral range from 1156.07 to 5054.95 nm (200 THz) at a −40 dB level, highlighting the versatility and broad applicability of our approach. And the proposed multi-octave MIR frequency comb is relevant for applications such as dual-comb spectroscopy and trace-gas sensing. Graphical Abstract

The fermented seed of néré (Parkia biglobosa), known as Soumbara, is a condiment widely consumed by the population in West Africa and Guinea in particular. The present study aims to use physicochemical, colorimetric methods and mid-infrared (MIR) spectroscopy to evaluate the evolution of the quality of Soumbara during storage (30 days). Thus, 5 kg of Soumbara were taken, subdivided into 7 batches of samples, and analysed every 5 days for 30 days. Physicochemical analyses (water activity, moisture, proteins, and total ash) would show that the storage duration induced a variation during storage; for example, the total ash contents on days 1, 5, 10, 15, 20, 25 and 30 are respectively 3.96 ± 0.25, 3.89 ± 0.43, 3.97 ± 0, 23, 3.99 ± 0.12, 4.54 ± 0.14, 4.57 ± 0.2 and 4.8 ± 0.21%. During the first 15 days of storage, no significant differences (p < 0.05) were observed between samples. The colorimetric measurements showed that the storage duration did not significantly affect the values of a* and b*, except the L* value which decreased significantly (p

With the rapid development of the nuclear industry，the amount of waste to be treated and monitored increases，and the potential emissions will also increase，and C-14 needs to be monitored. C-14 produced by nuclear facilities is mainly combined with CO2，so sensitive monitoring of 14CO2 gas is of great significance. In this paper，cavity ring-down spectroscopy (CRDS) is used to detect the CO2 absorption spectrum by selecting the center wave number of 14CO2 absorption line around 2209.11 cm−1. A CO2 detection system based on mid-infrared cavity ring-down spectroscopy is developed by using a quantum cascade laser in mid-infrared band，an optical resonator，and a reasonable optical path design and gas pipeline design. Based on the developed system，different concentrations of CO2 (0.5%-1.3%) were detected，and the experimental data were fitted and analyzed，and the results were found to be consistent with the theoretical formula，which confirmed the feasibility of the developed mid-infrared cavity ring-down spectrum system. The system has successfully realized the accurate measurement of different concentrations of CO2 gas in the mid-infrared band，the absorption spectrum of 14CO2 was measured by mid-infrared cavity ring-down technique， which provides an important technical support and foundation for the future study of laser spectral detection of 14CO2.

Nanophotonic structures have shown promising routes to controlling and enhancing nonlinear optical processes at the nanoscale. However, most nonlinear nanostructures require a handling substrate, reducing their application scope. Due to the underwhelming heat dissipation, it has been a challenge to evaluate the nonlinear optical properties of free-standing nanostructures. Here, we overcome this challenge by performing shot-controlled fifth harmonic generation (FHG) measurements on a SiC meta-membrane – a free-standing transmission metasurface with pronounced optical resonances in the mid-infrared (λ res ≈ 4,000 nm). Back focal plane imaging of the FHG diffraction orders and rigorous finite-difference time-domain simulations reveal at least two orders of magnitude enhancement of the FHG from the meta-membrane, compared to the unstructured SiC film of the same thickness. Single-shot measurements of the meta-membrane with varying resonance positions reveal an unusual spectral behavior that we explain with Kerr-driven intensity-dependent resonance dynamics. This work paves the way for novel substrate-less nanophotonic architectures.

Photoacoustic (PA) emitters are emerging ultrasound sources offering high spatial resolution and ease of miniaturization. Thus far, PA emitters rely on electronic transitions of absorbers embedded in an expansion matrix such as polydimethylsiloxane (PDMS). Here, it is shown that mid‐infrared vibrational excitation of C─H bonds in a transparent PDMS film can lead to efficient mid‐infrared photoacoustic conversion (MIPA). MIPA shows 37.5 times more efficient than the commonly used PA emitters based on carbon nanotubes embedded in PDMS. Successful neural stimulation through MIPA both in a wide field with a size up to a 100 µm radius and in single‐cell precision is achieved. Owing to the low heat conductivity of PDMS, less than a 0.5 °C temperature increase is found on the surface of a PDMS film during successful neural stimulation, suggesting a non‐thermal mechanism. MIPA emitters allow repetitive wide‐field neural stimulation, opening up opportunities for high‐throughput screening of mechano‐sensitive ion channels and regulators. [ABSTRACT FROM AUTHOR]

Low‐cost, room‐temperature operating light emitters in the 3–8 µm mid‐wave infrared wavelengths are desired for a broad range of applications such as chemical spectroscopy and infrared scene projection. The photoluminescence properties of PbSnSe ternary alloys grown by molecular beam epitaxy on (001) GaAs are studied in this work. Despite a large threading dislocation density, much greater than 109 cm−2, room temperature photoluminescence out to a peak wavelength of 8.4 µm is observed. In situ surface passivation with amorphous GeSe and an optimized thick PbSe buffer layer are shown to be necessary for enabling bright photoluminescence in PbSnSe heterostructures, stemming from Sn‐related defect complexes generated from ambient exposure and lying near the GaAs interface. Luminescence is found to be strongly blueshifted by unrelaxed tensile strains associated with thermal expansion and lattice constant mismatch, which makes emission wavelengths farther in the infrared more difficult to achieve. Carrier recombination analysis indicates room for further improvement as luminescence efficiencies are still limited by extrinsic mechanisms rather than intrinsic Auger recombination. Overall, this work demonstrates the exciting potential of PbSnSe for spontaneous emission in the mid‐wave infrared at room temperature, alongside more established material platforms like InAsSb. [ABSTRACT FROM AUTHOR]

Lead chalcogenides are compelling materials for nanophotonics and optoelectronics due to their high refractive indices, extreme thermo‐optic coefficients, and high transparency in the mid‐infrared (MIR). In this study, PbTe hoppercubes (HC, face‐open box cubes) are synthesized and explored for their MIR resonant characteristics. Single‐particle microspectroscopy uncovered deep‐subwavelength light localization, with a spectral response dominated by both fundamental and multiple high‐order Mie‐resonant modes. Nanoimaging mapping using scattering‐type scanning near‐field optical microscopy (s‐SNOM) reveals that the scattering at the center of the HC is reduced by more than five times compared to the edges. 2D‐Hyperspectral scans conducted using a low‐power broadband MIR source and nanometer spatial resolutions provided information on the local amplitude and phase‐resolved near‐fields, including amplitude and phase mapping of higher order modes with measured Q‐factors of close to 100. Employing s‐SNOM to characterize complex resonant nanophotonic structures holds implications for quantum sensing, IR photodetection, non‐linear generation, and ultra‐compact high‐Q metaphotonics. [ABSTRACT FROM AUTHOR]

The development of compact systems operating in the long‐wave infrared wavelength range is of high interest for spectroscopic and sensing applications. There is currently a wide interest toward the development of optical frequency‐combs to enhance the performances of these systems. Amongst the different techniques to obtain optical frequency‐combs, electro‐optic frequency‐comb generation presents major advantages thanks to the tunable repetition rate only limited by the bandwidth of the used electro‐optical modulator. However, the development of integrated and efficient electro‐optical modulators operating in a wide long‐wave infrared spectral band is still at its infancy, and electro‐optical frequency‐comb has not been demonstrated so far beyond 3 μm$\umu {\rm m}$ wavelength. In this work, a Schottky‐based modulator embedded in a Ge‐rich graded SiGe waveguide is used for electro‐optic frequency‐comb generation. Considering the limited efficiency of the modulator, harmonically‐rich RF signals are used to enhance the generation of comb lines around the optical carrier. Interestingly, this allows us to demonstrate the generation of electro‐optical combs spanning over 2.4 GHz around 8 μm$\umu {\rm m}$ wavelength. This paves the way toward fully integrated and tunable mid‐infrared electro‐optic frequency‐comb generation systems. [ABSTRACT FROM AUTHOR]

The development of new methods of identification of active pharmaceutical ingredients (API) is a subject of paramount importance for research centers, the pharmaceutical industry, and law enforcement agencies. Here, a system for identifying and classifying pharmaceutical tablets containing acetaminophen (AAP) by brand has been developed. In total, 15 tablets of 11 brands for a total of 165 samples were analyzed. Mid-infrared vibrational spectroscopy with multivariate analysis was employed. Quantum cascade lasers (QCLs) were used as mid-infrared sources. IR spectra in the spectral range 980–1600 cm−1 were recorded. Five different classification methods were used. First, a spectral search through correlation indices. Second, machine learning algorithms such as principal component analysis (PCA), support vector classification (SVC), decision tree classifier (DTC), and artificial neural network (ANN) were employed to classify tablets by brands. SNV and first derivative were used as preprocessing to improve the spectral information. Precision, recall, specificity, F1-score, and accuracy were used as criteria to evaluate the best SVC, DEE, and ANN classification models obtained. The IR spectra of the tablets show characteristic vibrational signals of AAP and other APIs present. Spectral classification by spectral search and PCA showed limitations in differentiating between brands, particularly for tablets containing AAP as the only API. Machine learning models, specifically SVC, achieved high accuracy in classifying AAP tablets according to their brand, even for brands containing only AAP. [ABSTRACT FROM AUTHOR]

A low‐cost single frequency laser, emitting in the mid‐infrared spectral region and dissipating minimal electrical power, is a key ingredient for the next generation of portable gas sensors for high‐volume applications involving chemical sensing of important greenhouse and pollutant gases. Herein, a Quantum Cascade Surface Emitting Laser (QCSEL) is proposed, which is implemented as a short linear cavity with high reflectivity coated end‐mirrors to suppress any edge emission and employs a buried semiconductor diffraction grating to extract the light from the surface. By wafer‐level testing, the cavity length scaling is investigated, mirror reflectivities larger than 0.9 are extracted, and a pulsed threshold power dissipation of 237 mW for an emission wavelength near 7.5 µm is achieved. Finally, single‐mode emission with a side‐mode suppression ratio larger than 33 dB is demonstrated for a 248 µm short cavity, which is mounted with the epitaxial layer up and operated in continuous wave at 20 ∘C$^{\circ}{\rm C}$. [ABSTRACT FROM AUTHOR]

Wide-field mid-infrared (MIR) hyperspectral imaging offers a promising approach for studying heterogeneous chemical systems due to its ability to independently characterize the molecular properties of different regions of a sample. However, applications of wide-field MIR microscopy are limited to spatial resolutions no better than ∼1 μm. While methods exist to overcome the classical diffraction limit of ∼λ/2, chromatic aberration from transmissive imaging reduces the achievable resolution. Here we describe the design and implementation of a simple MIR achromatic lens combination that we believe will aid in the development of resolution-enhanced wide-field MIR hyperspectral optical and chemical absorption imaging. We also examine the use of this doublet lens to image through polystyrene microspheres, an emerging and simple means for enhancing spatial resolution. [ABSTRACT FROM AUTHOR]

Ultra-broadband metamaterial absorbers (UBMAs) that are compatible with CMOS technology for use in the mid-infrared and long-wave infrared regions are crucial for a variety of applications, including radiative cooling, thermal photovoltaic, and thermal imaging. In this regard, we propose, in this work, a design of an UBMA based on the heavily doped silicon (D-Si) and silicon carbide (SiC). The 3D finite-difference time-domain method is used, mainly, to numerically calculate the optical characteristics of the proposed UBMA. The absorber, which is made up of a periodic array of symmetrical multilayered square rings of D-Si and SiC, achieves high absorption with an average absorption of 95% over a wavelength range of 2.5–22 µm. This broad range of wavelength absorption is attained, encompassing the mid-, long-wave, and partial far-infrared regions. In addition to the materials' inherent absorption, the stimulation of magnetic polaritons, surface plasmon polaritons, localized surface plasmon resonance, and cavity resonance are responsible for the nearly perfect broadband absorption. Under normal incidence, the proposed UBMA is polarization-independent due to the symmetrical design of the absorber. Furthermore, the impact of the incidence angle on the absorption of transverse electric and transverse magnetic waves is examined. [ABSTRACT FROM AUTHOR]

Manipulating the propagation of mid-infrared (mid-IR) light is crucial for optical imaging, biosensing, photocatalysis, and guiding photonic circuits. Artificially engineered metamaterials were introduced to comprehensively control optical waves. However, fabrication challenges and optical losses have impeded the progress. Fortunately, two-dimensional van der Waals (vdW) materials are alternatives because of their inherent optical properties, such as hyperbolic behavior, high confinement, low loss, and atomic-scale thickness. In this research, we conducted theoretical and numerical investigations on the α-phase molybdenum trioxide, a biaxial vdW material, with patterned graphene to assess the potential of the tunable focusing of mid-IR light. Our proposed method directly alters the path of excited light to focus mid-IR light by negative refraction. Further, the patterned graphene in our design offers enhanced focusing characteristics, featuring a significantly reduced waist diameter with 1/92 of the free-space wavelength, an enhanced beam quality without pronounced field ripples, and a fivefold increase in field intensity. Moreover, our approach significantly preserves the waist diameter of the focused beam while facilitating directional steering. Thus, the focused beam can propagate in a canalized manner toward the desired direction. These advancements lay the foundation for promising applications in planar photonics. [ABSTRACT FROM AUTHOR]

In this paper, we present a single crystal, KTA (potassium titanyl-arsenate, KTiOAsO4) based picosecond optical parametric amplifier pumped by an in-house built 1030 nm Yb:YAG thin-disk laser, capable of tunability from 1.46 to 3.5 µ m, operating at 90 kHz, with high average power in the signal and idler beams. The highest output power of 8.9 W was reached for the 1750 nm signal beam with 19% conversion efficiency and the respective 2500 nm idler beam power was 6.2 W with 13% efficiency. The highest combined signal and idler mid-infrared power was 17 W at the 2060 nm wavelength degeneracy point. [ABSTRACT FROM AUTHOR]

An approach to obtain easy-to-fabricate and spectrally selective nonreciprocal thermal emitter (NTE) has been proposed. The presented hybrid structure is composed of Weyl semimetal (WSM) film sandwiched by Ge/BaF2/Ge tri-layer and metal substrate. It has been shown that structural parameters hold tolerance on the order of hundreds of nanometers, which are highly favorable for fabricating with low cost and high performance. Multiband responses of the device can be realized through controlling the thickness of last Ge layer, which boosts the flexibility of preparation and potential applications. The giant nonreciprocity can be maintained with broad polar and azimuthal angle ranges. By manipulating the structural parameters, a remarkable result of nonreciprocal radiation is realized under both the transverse electric (TE) and transverse magnetic (TM) wave incidence. By changing the azimuthal angle (ϕi) of incidence, the nonreciprocity (η) can be effectively manipulated. The simulated η spectra is symmetric along the azimuthal angle ϕi=90°, and η=0 when ϕi=90°. Our results provide a much simpler way to achieve the multi-channel nonreciprocity and could lead to the advancement of power scavenging and conversion devices.

Highly responsive, low noise, and inexpensive photodetectors that operate in the mid‐infrared (MIR) wavelength regime are in high demand for applications ranging from fundamental science to large scale industries. However, simultaneously achieving all this in one device architecture is very challenging. In this work, mercury telluride (HgTe) colloidal quantum dot (cQD) based photodetectors are systematically improved by the introduction of new metamaterial designs. The new designs are found by utilizing simulations. Thereby the structures are optimized to increase the responsivity and simultaneously decrease the noise spectral current density. This is achieved by focusing on improving the photogenerated charge carrier collection efficiency while reducing the active material volume without altering the near unity absorption. A standard metamaterial perfect absorber architecture based on disc resonators is used as a starting point for the optimization process. By optimizing the carrier extraction through contact engineering, resulting in a narrow slot metamaterial, an overall ≈13‐fold responsivity and ≈345‐fold detectivity increase is achieved. The final metamaterial design reaches a responsivity of 16.2 A W−1 and detectivity of 6×108 Jones at a wavelength of 2710 nm. The analysis therefore provides a route to improve the responsivity and noise characteristics of mid‐infrared photodetectors based on cost‐efficient colloidal quantum dots. [ABSTRACT FROM AUTHOR]

We demonstrate substrate-emitting resonant cavity interband cascade light emitting diodes (RCICLEDs) based on a single distributed Bragg reflector (DBR). These devices operate in continuous wave mode at room temperature. Compared to standard ICLEDs without a cavity, we achieved an 89% reduction in the emission spectrum width, as indicated by the Full Width Half Maximum (FWHM) of 70 nm. Furthermore, we observed far-field narrowing and improved thermal stability. A single DBR configuration allows the cavity length to be adjusted by adding refractive index-matched material to the top of the epitaxial structure after epitaxial growth. This modification effectively shifts the cavity response towards longer wavelengths. We fabricated emitters comprising two cavities of different lengths, resulting in the emission of two distinct spectral lines that can be independently controlled. This dual-color capability enables one of the emission lines to serve as a built-in reference channel, making these LEDs highly suitable for cost-effective gas-sensing applications. [ABSTRACT FROM AUTHOR]

Multi-band circular dichroism (CD) response and tunability on the chiral metasurface are crucial for this device's applications in sensing and detection. This work proposes a dual-band CD Au-CaF2-Au dimer elliptical metasurface absorber, where chiroptical sensing is realized by breaking the geometric symmetry between two ellipses. The proposed metasurface can achieve high CD values of 0.8 and −0.74 for the dual-band within the 3–5 μm region, and the CD values can be manipulated by independently adjusting the geometric parameters of the metasurface. Furthermore, a slotted nanocircuit is introduced onto the metasurface to enhance its tunability by manipulating the geometry parameter in the design process, and the related mechanism is explained using an equivalent circuit model. The simulation of the sensing model revealed that the slotted nanocircuit enhances the sensor's tunability and significantly improves its bandwidth and sensitivity, achieving peak enhancements at approximately 753 nm and 1311 nm/RIU, respectively. Due to the strong dual-band positive (and negative) responses of the CD values, flexible wavelength tunability, and nonlinear sensitivity enhancement, this design provides a new approach for the development and application of mid-infrared chiroptical devices. [ABSTRACT FROM AUTHOR]

The early detection of gynecological cancers, which is critical for improving patient survival rates, is challenging because of the vague early symptoms and the diagnostic limitations of current approaches. This comprehensive review delves into the game-changing potential of infrared (IR) spectroscopy, a noninvasive technology used to transform the landscape of cancer diagnosis in gynecology. By collecting the distinctive vibrational frequencies of chemical bonds inside tissue samples, Fourier-transform infrared (FTIR) spectroscopy provides a 'molecular fingerprint' that outperforms existing diagnostic approaches. We highlight significant advances in this field, particularly the identification of discrete biomarker bands in the mid- and near-IR spectra. Proteins, lipids, carbohydrates, and nucleic acids exhibited different absorption patterns. These spectral signatures not only serve to distinguish between malignant and benign diseases, but also provide additional information regarding the cellular changes associated with cancer. To underscore the practical consequences of these findings, we examined studies in which IR spectroscopy demonstrated exceptional diagnostic accuracy. This review supports the use of IR spectroscopy in normal clinical practice, emphasizing its capacity to detect and comprehend the intricate molecular underpinnings of gynecological cancers. [ABSTRACT FROM AUTHOR]

Guided-mode resonance (GMR) is a compelling scheme for optical sensing of various physical quantities, which holds great promise in non-invasive detection of chemical and biological species. Current GMR sensors are mostly based on detection of environmental refractive index change, which presents a challenge for obtaining sensing selectivity as required in practical applications. In this work, we report on a prototype demonstration of using GMR for detecting molecular fingerprint absorption. In a waveguide grating made of a ZnSe layer sandwiched between a Cu film and an Au grating, a mid-infrared GMR is excited and tuned over a wide frequency range of 617.4 cm−1. Coupling of the GMR with a polydimethylsiloxane (PDMS) analyte film reveals the signature absorptions of CH2 group, whose vibrational signal is enhanced by a factor of 2.37 at a frequency detuning of 30 cm−1 between the GMR and the molecular vibration. Our theoretical analysis reveals that both near-field enhancement of GMR and its coupling strength with molecules are responsible for the molecular detection performance. These results suggest that angle-tuned GMR presents an alternative design paradigm for surface-enhanced infrared absorption spectroscopy (SEIRAS). [ABSTRACT FROM AUTHOR]

This study proposes the design of a novel Metal-Insulator-Metal (MIM) nano-infrared emitter that uses a unique diamond-shaped grating to achieve selective infrared absorption. Diamond-shaped nano emitter (DNE) structure exhibits four narrow resonant peaks within key absorption windows such as short-wave infrared (SWIR) mid-wave infrared (MWIR), alongside with a wide absorption band in the Non-Transmissive Infrared Range (NTIR) for thermal camouflage applications compatible with radiative cooling. Moreover, the proposed DNE is polarization insensitive as it has an in-plane symmetric design. Using the 3D Finite-Difference Time-Domain (FDTD) simulations, we demonstrate the nanoantenna's superior performance characterized by its high absorption rates and tuned effective impedance matching. As of our knowledge, the findings suggest that this is the first time that a MIM structure achieved multiple narrow resonance peaks, located in SWIR and MWIR simultaneously, with a wide absorption range in NTIR. Represented DNE stands as a significant innovation in the field of stealth technology, providing a tunable, high-efficiency solution for managing and controlling thermal emissions across diverse applications. [ABSTRACT FROM AUTHOR]

Mid-infrared (mid-IR) photodetection is important for various applications, including biomedical diagnostics, security, chemical identification, and free-spacing optical communications. However, conventional "photon" mid-IR photodetectors require liquid nitrogen cooling (i.e., MCT). Furthermore, acquiring mid-IR spectra usually involves a complex and expensive Fourier Transform Infrared spectrometer, a tabletop instrument consisting of a meter-long interferometer and MCT detectors, which is not suitable for mobile and compact device applications. In this work, we present tunable photoresponsivity in the mid-IR wavelength in palladium diselenide (PdSe2) – molybdenum disulfide (MoS2) heterostructure field-effect transistors (FETs), operating at room temperature. Furthermore, we applied a tunable membrane cavity to modulate the Fabry–Pérot resonance to modulate the absorption spectrum of the device layer. We used a robust polyetherimide (PEI) membrane with CVD-grown graphene to electrically tune the membrane structure. For the next step, we will integrate the PdSe2-based photodetector and tunable membrane to increase detection sensitivity and spectrum tunability to realize the 'learning'-based spectroscopy. [ABSTRACT FROM AUTHOR]

Mid-infrared (mid-IR) photodetection is important for various applications, including biomedical diagnostics, security, chemical identification, and free-spacing optical communications. However, conventional "photon" mid-IR photodetectors require liquid nitrogen cooling (i.e., MCT). Furthermore, acquiring mid-IR spectra usually involves a complex and expensive Fourier Transform Infrared spectrometer, a tabletop instrument consisting of a meter-long interferometer and MCT detectors, which is not suitable for mobile and compact device applications. In this work, we present tunable photoresponsivity in the mid-IR wavelength in palladium diselenide (PdSe2) – molybdenum disulfide (MoS2) heterostructure field-effect transistors (FETs), operating at room temperature. Furthermore, we applied a tunable membrane cavity to modulate the Fabry–Pérot resonance to modulate the absorption spectrum of the device layer. We used a robust polyetherimide (PEI) membrane with CVD-grown graphene to electrically tune the membrane structure. For the next step, we will integrate the PdSe2-based photodetector and tunable membrane to increase detection sensitivity and spectrum tunability to realize the 'learning'-based spectroscopy. [ABSTRACT FROM AUTHOR]

Spectroscopy is a powerful tool to identify the specific fingerprints of analytes in a label-free way. However, conventional sensing methods face unavoidable barriers in analyzing trace-amount target molecules due to the difficulties of enhancing the broadband molecular absorption. Here, we propose a sensing scheme to achieve strong fingerprint absorption based on the angular-scanning strategy on an all-silicon metasurface. By integrating the mid-infrared and terahertz sensing units into a single metasurface, the sensor can efficiently identify 2,4-DNT with high sensitivity. The results reveal that the fingerprint peak in the enhanced fingerprint spectrum is formed by the linked envelope. It exhibits a significant enhancement factor exceeding 64-fold in the terahertz region and more than 55-fold in the mid-infrared region. Particularly, the corresponding identification limit of 2,4-DNT is 1.32 µg cm−2, respectively. Our study will provide a novel research idea in identifying trace-amount explosives and advance practical applications of absorption spectroscopy enhancement identification in civil and military security industries. [ABSTRACT FROM AUTHOR]

Perfluoride glass ceramics (FGCs) with SrF 2 /CaF 2 mixed crystals were prepared using a concurrent rapid-quenching-crystallization process. The FGCs contained dense, homogeneous, round crystals of sizes less than 1 μm with high transmittance (exceeding 80 % at 3–8 μm) and low phonon energy (508 cm−1). The fluorescence properties of the FGCs doped with Er and Dy were investigated. The energy transfer efficiency between Er and Dy reached 93.81 % and 98.13 %, corresponding to Er: 4I 11/2 to Dy: 6H 5/2 and Er: 4I 13/2 to Dy: 6H 11/2 , respectively. This enhancement is attributed to the enrichment of rare-earth ions in the crystals induced by phase-separation and low phonon energy of the host material, FGC. Moreover, the average lifetime of Er: 4I 11/2 in FGC reached 10.13 ms, which is the highest reported value for glass ceramics to our knowledge. This study enriches the research theory of FGC and provides guidance for expanding the properties of materials for mid-infrared photonics. [ABSTRACT FROM AUTHOR]

It is extremely challenging to accomplish second‐harmonic generation (SHG) in the whole mid‐infrared (MIR) region for oxide crystals due to their short IR absorption cutoff wavelengths. Herein, a new MIR nonlinear optical (NLO) crystal of K4ZnV5O15Cl (KZVC) is designed and synthesized by the aliovalent substitution of [VIIIO5] with [ZnIIO4Cl] based on the K2(VO)(V2O7) matrix. KZVC features an ordered 2D [ZnV5O15Cl]∞ layered structure comprising [ZnO4Cl] / [VO5] square pyramids and [VO4] tetrahedron as functional units. Importantly, KZVC shows excellently balanced performances of strong SHG responses (12 × KDP @ 1064 nm, 1.1 × AgGaS2 @ 2.05 µm), broad IR transparency range (0.52‒10 µm), congruent‐melting behavior, and highest laser‐induced damage threshold (LIDT) (60 × AgGaS2 @ 1064 nm) among the reported vanadates. Most remarkably, KZVC represents the first example in the oxide‐based IR NLO crystals that can achieve phase matching in a wide wavelength range extending from 1.8 to 10 µm, fully covering the important MIR atmospheric windows (3‒5 µm). [ABSTRACT FROM AUTHOR]

Plasmonic spectral filters composed of periodic nanostructured metal films offer novel opportunities for the development of multispectral imaging technologies in the mid-infrared region. However, traditional plasmonic filters, which typically feature simplistic structures such as nanoholes or nanorings, are constrained by a narrow bandpass and significant crosstalk, leading to limited practical performance. Filters designed using inverse techniques allow a substantial degree of freedom in creating intricate structures that align with desired spectral characteristics, including a quasi-square spectral profile, high transmission, wide full width at half maximum, and reduced crosstalk. In this study, we have utilized an inverse design algorithm to engineer high-performance bandpass filters for the mid-infrared range, achieving an average transmittance exceeding 80% within the bandpass window and below 10% in the stop band, which is comparable to that of commercial multilayer Bragg filters. Nanofabrication processes were employed to transfer the designed pattern into the gold film on ZnS substrate that is transparent in the mid-infrared range. The resulting filters exhibit spectral performance analogous to that of the inversely designed models, making them suitable for direct integration with mid-infrared photodetector arrays in multispectral imaging systems. [ABSTRACT FROM AUTHOR]

Precision measurements on molecules in the strong fundamental bands are of great importance. An ac curate mid-infrared light source is a key for these studies. By locking the signal and pump light to an optical frequency comb, a high-precision continu ous-wave optical parametric oscillator source is built, and the mid-infrared frequency drift is deter mined to be less than 1 kHz. As a demonstration, saturated absorption spectroscopy of the R(14) (00011)–(00001) line of 13CO2 is measured, and the transition frequency is determined to be 68786813496(29) kHz. The frequency-stabilized mid-infrared laser source provides an opportunity for precision measurements of molecules in fundamental bands. [ABSTRACT FROM AUTHOR]

This study reports the experimental demonstration of the first waveguide-integrated SiGe modulator using a PIN diode operating in a wide spectral range of the mid-infrared region. At the wavelength of 10 µm, an extinction ratio up to 10 dB is obtained in injection regime and 3.2 dB in depletion regime. High speed operation is obtained, up to 1.5 GHz. Furthermore, the device can also operate as an integrated photodetector. Photodetection has thus been characterized from 5.2 µm to 10 µm wavelengths showing an internal responsivity around 1 mA/W, and a 3 dB electro-optical bandwidth of 32 MHz. These results show a significant advancement in integrated photodetectors and electro-optical modulators for mid-infrared spectroscopy. [ABSTRACT FROM AUTHOR]