Mid-infrared Range Research Articles

Mid-infrared computational temporal ghost imaging

Ghost imaging in the time domain allows for reconstructing fast temporal objects using a slow photodetector. The technique involves correlating random or pre-programmed probing temporal intensity patterns with the integrated signal measured after modulation by the temporal object. However, the implementation of temporal ghost imaging necessitates ultrafast detectors or modulators for measuring or pre-programming the probing intensity patterns, which are not available in all spectral regions especially in the mid-infrared range. Here, we demonstrate a frequency downconversion temporal ghost imaging scheme that enables to extend the operation regime to arbitrary wavelengths regions where fast modulators and detectors are not available. The approach modulates a signal with temporal intensity patterns in the near-infrared and transfers the patterns to an idler via difference-frequency generation in a nonlinear crystal at a wavelength where the temporal object can be retrieved. As a proof-of-concept, we demonstrate computational temporal ghost imaging in the mid-infrared with operating wavelength that can be tuned from 3.2 to 4.3 μm. The scheme is flexible and can be extended to other regimes. Our results introduce new possibilities for scan-free pump-probe imaging and the study of ultrafast dynamics in spectral regions where ultrafast modulation or detection is challenging such as the mid-infrared and THz regions.

Low-Loss Buried InGaAs/InP Integrated Waveguides in the Long-Wave Infrared.

In this work, we present a photonic integrated platform based on buried InGaAs waveguides with InP cladding that operates over a large mid-infrared (mid-IR) spectral range. Thanks to wet-etch fabrication patterning and Fe doping, low propagation losses below 1.2 dB/cm (0.3 cm-1 loss coefficient) have been obtained between 4.6 and 11.2 μm wavelengths (890-1960 cm-1 wavenumber), in both transverse electric (TE) and transverse magnetic (TM) polarization modes. The possibility of monolithically integrating such waveguides with mid-IR sources offers promising perspectives for developing broadband, homogeneously integrated systems.

An Ultra-broadband Metallic Plasmonic Antenna for Ultrasensitive Molecular Fingerprint Identification.

Near-field enhanced mid-infrared light-matter interactions via metallic plasmonic antennae (PA) have attracted much attention but are inevitably limited by the detuning between their narrow band and the broad applied spectral range. Here, we develop a new low-temperature incubation synthetic method to acquire uniform Ag microparticles (MPs) with numerous hotspots. Their plasmonic band is remarkably extended by the plasmonic coupling of numerous hotspots and covers the entire mid-infrared range (400-4000 cm-1). Hence, the almost complete molecular fingerprint of 4-mercaptobenzonitrile was successfully probed for the first time via resonant surface-enhanced infrared absorption (rSEIRA), and the rSEIRA spectra of different essential amino acids were further detected and exhibit a high spectral identification degree assisted by machine learning. This work changes the inertia perception of "narrow band and large size but small hotspot area" of mid-infrared metallic PA and paves the way for the ultrasensitive mid-infrared optical sensing.

Dual-band high quality-factor perfect absorber based on uniaxial/biaxial anisotropic van der Waals polar crystals

Phonon polaritons (PhPs) in two-dimensional van der Waals crystals, such as hexagonal boron nitride (hBN) and α-phase molybdenum trioxide (α-MoO3), exhibit remarkable spatial confinement and extremely low optical losses, offering possibilities for the development of novel micro and nanophotonic devices at mid-infrared wavelengths. Here, we demonstrate the potential of the proposed Tamm structure to achieve dual-band high quality-factor perfect absorption within the mid-infrared range. This structure utilizes upper and lower spacer layers to isolate the anisotropic materials hBN and α-MoO3 from one-dimensional photonic crystals, where the Tamm phonon polaritons (TPhPs) are respectively excited at the interfaces, facilitating strong coupling with incident light and leading to significant dual-band perfect absorption phenomena. The results demonstrate that due to polariton resonances, the absorption peaks exhibit extremely narrow absorption bandwidths, with the maximum quality-factor reaching up to 297. In addition, tunable resonant wavelengths and polarization-dependent absorption properties are also demonstrated in the proposed Tamm structure. This study provides an alternative and straightforward approach for constructing dynamic and multifunctional optical devices such as optical modulators, tunable multi-band filters and biosensors.

In situ investigation of the atomic structure of carbonate-silicate liquids at high pressure-temperature and spectroscopic characterization of the recovered quenched glasses

Carbonate-silicate melts that originate in Earth's interior are described as transitional melts which possess compositions intermediate between carbonatitic and basaltic end members. The covariation of key oxides between carbonatite and basalt (e.g., 10–35 wt% SiO2 and 40–10 wt% CO2, respectively) is expected to have a strong effect on liquid properties. However, due to their paucity both in the record of terrestrial rocks and as quenched glasses, their molecular structure has remained poorly explored to date. We investigated the atomic structure of a synthetic carbonate-silicate liquid with chemical composition within the CaO-MgO-Al2O3-SiO2-FeO-Na2O-ClO−-CO2 oxide system having 18.28 wt% SiO2 and 22.54 wt% CO2 using multi-angle energy dispersive X-ray diffraction at pressures (P) and temperatures (T) of 1.4 GPa/1815 °C, 2.6 GPa/1865 °C, 4.3 GPa/1990 °C, 4.4 GPa/1950 °C. The results show that the intermediate range ordering of the structure decreases with an increase of both P and T. Based on this study, the carbonate-silicate magmas at upper mantle P-T conditions are expected to increase their viscosities during their ascent through the mantle as a result of increasing intermediate range ordering upon cooling and decompression. Additionally, spectroscopic measurements were carried out on the quenched glasses at ambient pressure using micro-Raman as well as micro-FTIR in reflection and transmission modes in the mid infrared range. High pressure investigation using micro-FTIR was also conducted. The distribution of Qn species obtained by deconvolution of the Raman spectra within the aluminosilicate region confirms the depolymerized nature of the quenched glasses as inferred by the low viscosities of the corresponding liquids; peculiar characteristics of the C vibrations would suggest a distorted environment surrounding the network modifying CO32− anion. No evidence of molecular CO2 was detected. Notably, we find evidence of both dissolved molecular CO and CO linked to a metal cation forming carbonyl complexes in the quenched glasses at P-T-fo2 conditions compatible with a hot Archean upper mantle. This suggests a role for carbonate-silicate magmas as carriers of reduced gaseous C-O-H species towards the early atmosphere along with the mobilization of PGE-elements.

Mid-IR supercontinuum generation in a silicon nitride loaded lithium niobate on sapphire waveguide

In spectroscopy, having access to a wide range of wavelengths within the mid-infrared region is crucial for conducting thorough and versatile analyses. In our research, we successfully demonstrate numerically the generation of supercontinuum within a waveguide made of silicon nitride loaded onto lithium niobate on a sapphire substrate, with a specific focus on the mid-infrared wavelength range. By implementing effective lateral leakage and dispersion engineering techniques, we have significantly broadened our system’s spectral range, covering wavelengths from the near-infrared (near-IR) to the mid-infrared (mid-IR) regions. Our results indicate that when a silicon nitride-loaded lithium niobate waveguide is excited with a commercially available femtosecond fiber laser pump at 2070 nm, it has the capability to produce a supercontinuum that spans more than one octave within the mid-infrared wavelength range.

Mid-infrared interferometry with non-adiabatic tapered ZBLAN optical fiber

This work illustrates, to the best of our knowledge, the first non-adiabatic tapered single-mode zirconium fluoride optical fiber sensor in the mid-infrared spectral range. It is designed and fabricated via pulling and heating technique. A waist diameter d w = 25 µm with no visible crystallization is achieved, overcoming the typical fluoride glass challenges associated with crystallization, narrow temperature fabrication window, and low glass transition temperature. The performance of the non-adiabatic tapered optical fiber is theoretically and experimentally investigated, demonstrating its high potential for a wide range of sensing applications in the mid-infrared spectral range.

A proposal for a fast infrared bursts detector

The gravitational wave GW170817 from a binary neutron star merger and the simultaneous electromagnetic detection of the GRB170717A by Fermi Gamma-Ray Space Telescope, opened a new era in the multi-messenger astronomy. Furthermore, the GRBs (Gamma-Ray Bursts) and the mysterious FRBs (Fast Radio Bursts) have sparked interest in the development of new detectors and telescopes dedicated to the time-domain astronomy across the electromagnetic spectrum. Time-domain astronomy aims to acquire fast astronomical bursts in temporal range between a few seconds down to 1 ns. Fast InfraRed Bursts (FIRB's) have been relatively understudied, often due to the lack of appropriate tools for observation and analysis. In this scientific scenario, the present contribution proposes a new detection system for ground-based reflecting telescopes working in the mid-infrared (mid-IR) range to search for astronomical FIRB's. Experience developed in the diagnostics for lepton circular accelerators can be used to design temporal devices for astronomy. Longitudinal diagnostic instruments acquire bunch-by-bunch particle shifts in the direction of flight, that is equivalent to temporal. Transverse device integrates the beam signal in the horizontal and vertical coordinates, as standard telescopes. The proposed instrument aims to work in temporal mode. Feasibility study tests have been carried out at SINBAD, the infrared beam line of DAFNE, the e+e- collider of INFN. SINBAD releases pulsed infrared synchrotron light with 2.7 ns separation. The front-end detector system has been evaluated to detect temporal fast infrared signals with 2–12 μm wavelengths and 1 ns rise times. The present contribute aims to be a step toward a feasibility study report.

Data encryption with chaotic light in the long wavelength infrared atmospheric window

In environments where traditional fiber optic cables are impractical, free-space optical communications offer a promising solution for transmitting large amounts of data, especially in the mid-infrared wavelength range. Despite the advantages of minimal atmospheric interference and stable signals, the vulnerability of wireless optical communications to eavesdropping poses a significant challenge. This study addresses this challenge by demonstrating a method for privately transmitting optical data using photonic chaos from distributed feedback quantum cascade lasers operating at 9.3 µm. Signal processing techniques are applied to enhance the quality of the transmission over distances exceeding 30 m, accompanied by a comprehensive analysis of the photonic chaos complexity to ensure data confidentiality. These findings mark a significant advancement in developing private communications systems within the thermal atmospheric window, with a substantially reduced risk of interception by adversaries. The research not only contributes to secure communications but also has potential implications for enhancing security of data transmission in challenging environments, impacting various industries and applications.

Harmonic and anharmonic vibrational computations for biomolecular building blocks: Benchmarking DFT and basis sets by theoretical and experimental IR spectrum of glycine conformers.

Advanced vibrational spectroscopic experiments have reached a level of sophistication that can only be matched by numerical simulations in order to provide an unequivocal analysis, a crucial step to understand the structure-function relationship of biomolecules. While density functional theory (DFT) has become the standard method when targeting medium-size or larger systems, the problem of its reliability and accuracy are well-known and have been abundantly documented. To establish a reliable computational protocol, especially when accuracy is critical, a tailored benchmark is usually required. This is generally done over a short list of known candidates, with the basis set often fixed a priori. In this work, we present a systematic study of the performance of DFT-based hybrid and double-hybrid functionals in the prediction of vibrational energies and infrared intensities at the harmonic level and beyond, considering anharmonic effects through vibrational perturbation theory at the second order. The study is performed for the six-lowest energy glycine conformers, utilizing available "state-of-the-art" accurate theoretical and experimental data as reference. Focusing on the most intense fundamental vibrations in the mid-infrared range of glycine conformers, the role of the basis sets is also investigated considering the balance between computational cost and accuracy. Targeting larger systems, a broad range of hybrid schemes with different computational costs is also tested.

Passive daytime radiative cooling composite films with super-amphiphobic, friction-resistant and flame-retardant properties

Ensuring prolonged performance is a challenge in promoting passive daytime radiative cooling materials (PDRCMs) for addressing energy depletion. A single-layer inlay-structured passive daytime radiative cooling composite film (PDRCCF) was introduced with hexagonal boron nitride (h-BN) in polydimethylsiloxane (PDMS) and randomly semi-embedded fluorination-modified barium sulfate (M-BaSO4) particles on the substrate surface. The optimal sample demonstrated high average reflectivity of 94.73% in the solar spectrum (SS), average emissivity of 95.96% in the mid-infrared wavelength range (MIWR) (2.5–25 μm) and average daytime temperature drop of 4.21°C in cloudy weather, and also exhibited super-amphiphobic, friction-resistant and flame-retardant properties due to the h-BN and M-BaSO4 particles. This work offers a significant strategy for advancing PDRCMs.

Coherent light-emitting metasurfaces based on bound states in the continuum

Abstract An emergent need exists for solid state tunable coherent light emitters in the mid-infrared range for spectroscopy, sensing, and communication applications where current light sources are dominated by spontaneous emitters. This paper demonstrates a distinct class of coherent thermal emitters operating in the mid-infrared wavelength regime. The structure of the light source consists of a dielectric metasurface fabricated on a phononic substrate. In this study, we present the first implementation of off-Γ Friedrich–Wintgen bound states in the continuum at mid-infrared wavelengths suitable for developing the next generation of coherent light emitters. Numerical analysis of the emissivity spectrum reveals the interference of resonances leading to avoided crossings and the formation of Friedrich–Wintgen bound states in the radiation spectrum. Additionally, significant localized field enhancements are observed within the metasurface at operating wavelengths. The emissivity spectra measured by reflectivity and emission experiments exhibit temporally coherent emission peaks in the vicinity of the bound state in the continuum, the first such demonstration in the mid-infrared region for wavelengths longer than 7 µm. These results represent a new approach for significant advancement in realizing mid-infrared coherent light emitters with promising implications for future technologies.

From weak to strong coupling: quasi-BIC metasurfaces for mid-infrared light-matter interactions.

Thanks to their giant, yet tunable, Q-factor resonances, all-dielectric metasurfaces supporting the quasi-bound states in the continuum (q-BIC) resonances are well-suited to provide a promising platform for quantum-coherent light-matter interactions. Yet, the strong coupling regime, characterized by the hybrid light-matter states - polaritons, has not yet been fully explored in the mid-infrared regime. This paper investigates the parameter space of vibrational strong coupling (VSC) between material and metasurface cavities supporting q-BIC resonances in the mid-infrared spectral range. We outline the effects of transition dipole strength, damping rate, and the number of molecules coupled to a single cavity, as well as the cavity damping rates, to understand their respective impacts on VSC. By tuning the Q-factor of the metasurface and material parameters, a new transition light-matter coupling zone is introduced, bridging the gap between weak and strong coupling, where polaritons form but their linewidths prohibit their spectral identification. The study further identifies the effects of cavity linewidth on polariton peak separability in strongly coupled systems, highlighting that the cavities with smaller nonradiative losses and narrower linewidths facilitate better polariton separability. Moreover, we found that matching cavity and material loss, satisfying the critical strong coupling condition, enhances the coupling strength between cavity and material. Overall, these findings can guide the design of photonic cavities suited for VSC experiments, contributing to the burgeoning fields of polaritonic chemistry, light-mediated modulation of chemical reactivity, and highly sensitive molecular spectroscopy.

Temporal dynamics of surface phonon polaritons in polar dielectric nanoparticles with nonlocality

Surface phonon polaritons (SPhPs) supported by polar dielectrics have been a promising platform for nanophotonics in mid-infrared spectral range. In this work, the temporal dynamic behavior of polar dielectric nanoparticles without (or with) spatial dispersion/nonlocality driven by the ultrashort Gaussian pulses is carried out. We demonstrate that three possible scenarios for the temporal evolutions of the dipole moment including ultrafast oscillations with the decay, exponential decay, and keeping a Gaussian shape exist, when the pulse duration of the incident field is much shorter than, similar to, and much longer than the localized SPhP lifetime. Once the nonlocal effect is considered, the oscillation period becomes large slightly, and the exponential decay turns fast. Furthermore, nonlocality-induced novel temporal behavior is found such as the decay with long-period oscillations when the center frequency of the incident pulse lies at the frequency of adjacent longitudinal resonant modes. The positive and negative time-shifts of the dielectric response reveal that the excitation of the dipole moment will be delayed or advanced. These temporal evolutions can pave the way towards potential applications in the modulation of ultrafast signals for the mid-infrared optoelectronic nanodevices.

Third order nonlinear correlation of the electromagnetic vacuum at near-infrared frequencies

In recent years, electro-optic sampling, which is based on Pockel’s effect between an electromagnetic mode and a copropagating, phase-matched ultrashort probe, has been largely used for the investigation of broadband quantum states of light, especially in the mid-infrared and terahertz frequency range. The use of two mutually delayed femtosecond pulses at near-infrared frequencies allows the measurement of quantum electromagnetic radiation in different space-time points. Their correlation allows therefore direct access to the spectral content of a broadband quantum state at terahertz frequencies after Fourier transformation. In this work, we will prove experimentally and theoretically that when using strongly focused coherent ultrashort probes, the electro-optic sampling technique can be affected by the presence of a third-order nonlinear mixing of the probes’ electric field at near-infrared frequencies. Moreover, we will show that these third-order nonlinear phenomena can also influence correlation measurements of the quantum electromagnetic radiation. We will prove that the four-wave mixing of the coherent probes’ electric field with their own electromagnetic vacuum at near-infrared frequencies results in the generation of a higher-order nonlinear correlation term. The latter will be characterized experimentally, proving its local nature requiring the physical overlap of the two probes. The parameters regime where higher order nonlinear correlation results predominant with respect to electro-optic correlation of terahertz radiation is provided.

Exploring the hardness of the ionising radiation with the infrared softness diagram

Aims. We explored the softness parameter in the infrared, ηIR′, whose main purpose is the characterisation of the hardness of the incident ionising radiation in emission-line nebulae. This parameter is obtained from the combination of mid-infrared wavelength range transitions corresponding to consecutive ionisation stages in star-forming regions. Methods. We compiled observational data from a sample of star-forming galaxies (SFGs), including luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs), to study the ηIR′ and its equivalent expression in two dimensions, the softness diagram. We compared them with predictions from photoionisation models to determine the shape of the ionising continuum energy distribution in each case. We also used the measured emission-line ratios as input for HCMISTRY-TEFF-IR, a code that performs a Bayesian-like comparison with photoionisation model predictions in order to quantify the equivalent effective temperature (T*) and the ionisation parameter. Results. We found similar average values within the errors of ηIR′ in (U)LIRGs (−0.57) in the rest of the SFGs (−0.51), which could be interpreted as indicative of a similar incident radiation field. This result is confirmed from the analysis using HCM-TEFF-IR, which simultaneously points to a slightly lower, although similar within the errors, T* scale for (U)LIRGs, even when a higher dust-to-gas mass ratio is considered in the models for these objects. These derived T* values are compatible with the ionisation from massive stars, without any need of harder ionising sources, both for (U)LIRGs and the rest of the SFGs. However, the derived T* in (U)LIRGs do not show any correlation with metallicity. This could be interpreted as a sign that their similar average T* values are due to the attenuation of the energetic incident flux from massive stars by the heated dust mixed with the gas. This is supported by the known very large amounts of small grains associated with the very high star formation rates measured in galaxies of this type.

Tunable Near and Mid-Infrared (1.3–5 µm) Picosecond Pulsed Optical Vortex Parametric Oscillator

In this paper, we present a picosecond pulsed, synchronously pumped optical parametric oscillator producing vortex beam output with tunable wavelengths in the near- to mid-infrared range. The system utilizes a Nd:YVO4 picosecond pulsed solid-state laser emitting at a wavelength of 1.064 µm to pump a Z-shaped, singly resonant OPO which contains a MgO:PPLN crystal with a fan-shaped grating. The wavelength tuning characteristics of the OPO output are examined both as a function of the MgO:PPLN grating period and crystal temperature. The orbital angular momentum of the pump field can be selectively transferred to either the signal or idler fields by appropriately adjusting the location of the MgO:PPLN crystal within the OPO cavity. The maximum output power of the signal and idler vortex fields are 5.12 W and 3.46 W, respectively, for an incident pump power of 19 W.

A non-destructive measuring device in the mid-infrared range for measuring the CO2 concentration in the headspace of food packaging

Carbon dioxide (CO2) is the most common gas used in modified atmosphere packaging (MAP) to protect packaged foods from spoilage and pathogenic microorganisms and thus extend the shelf life of food products. Non-destructive measurement of CO2 concentration of the packaging headspace is of great interest as it could be used at various stages of the value chain, from outgoing goods inspection to storage tests and possible monitoring of the modified atmosphere at retail. Therefore, the aim of this work was to develop a measuring device operating non-destructively on closed MAP trays. Absorption measurement in the mid-infrared range at four different wavelengths proved to be a suitable principle for determining the CO2 gas concentration in a closed packaging system: 4.26 μm (2347 cm−1) and 4.27 μm (2342 cm−1) in the range of the antisymmetric stretching vibration, as well as 4.45 μm (2247 cm−1) at the edge of the antisymmetric stretching vibration, and 3.95 μm (2532 cm−1) as a reference measurement outside the absorption band with a thermal infrared source. Measurement principle and setup - the measurement in the absorbing and non-absorbing range and the guiding of the thermal infrared (IR) emitter at a 45° angle through the corner of the tray - allows a measurement largely independent of tray shape, height, and packaged product. The measurement can also be used for pigmented and printed trays - except for carbon black pigments. Optical impairments of the packaging and labeled areas of the lidding film appeared to have the greatest influence on the measurement accuracy. The applicability of the measurement system was evaluated and successfully demonstrated using commercially available food packaging from a local supermarket by comparing the CO2 gas concentrations yielded with those obtained using a destructive measurement device.

Hybridization of graphene-gold plasmons for active control of mid-infrared radiation

Many applications in environmental and biological sensing, standoff detection, and astronomy rely on devices that operate in the mid-infrared range, where active devices can play a critical role in advancing discovery and innovation. Nanostructured graphene has been proposed for active miniaturized mid-infrared devices via excitation of tunable surface plasmons, but typically present low efficiencies due to weak coupling with free-space radiation and plasmon damping. Here we present a strategy to enhance the light-graphene coupling efficiency, in which graphene plasmons couple with gold localized plasmons, creating novel hybridized plasmonic modes. We demonstrate a metasurface in which hybrid plasmons are excited with transmission modulation rates of 17% under moderate doping (0.35 eV) and in ambient conditions. We also evaluate the metasurface as a mid-infrared modulator, measuring switching speeds of up to 16 kHz. Finally, we propose a scheme in which we can excite strongly coupled gold-graphene gap plasmons in the thermal radiation range, with applications to nonlinear optics, slow light, and sensing.

Far- and mid-infrared FT-IR analysis of the single-crystal pentacene using a linearly polarized synchrotron radiation light source

Understanding and control of molecular vibrations are essential aspects for both fundamental and application considerations of organic semiconductor electronics. The reason is that the organic electronic devices are driven by diverse electronic processes in molecular solids, such as charge carrier transport and excitonic progression, that are strongly influenced by coupling with vibrations. In the present study, molecular vibrations of single-crystals of pentacene, a representative organic semiconductor material, were examined in the far- to mid-infrared range by means of Fourier transform infrared (FT-IR) spectroscopy using a linearly polarized synchrotron radiation light source. The IR absorption spectra exhibited significant modulation depending on the crystalline in-plane azimuthasl angle of c*-oriented single-crystal pentacene.