IR Photons Research Articles

Germanium Single Crystals for Photonics

Germanium (Ge) is a system-forming material of IR photonics for the atmospheric transparency window of 8–14 µm. For optics of the 3–5 µm range, more widespread silicon (Si), which has phonon absorption bands in the long-wave region, is predominantly used. A technology for growing Ge single crystals has been developed, allowing the production of precision optical parts up to 500 mm in diameter. Ge is used primarily for the production of transparent optical parts for thermal imaging devices in the 8–14 µm range. In addition, germanium components are widely used in a large number of optical devices where such properties as mechanical strength, good thermal properties, and climatic resistance are required. A very important area of application of germanium is nonlinear optics, primarily acousto-optics. The influence of doping impurities and temperature on the absorption of IR radiation in germanium is considered in detail. The properties of germanium photodetectors are reported, primarily on the effect of photon drag of holes. Optical properties in the THz range are considered. The features of optical properties for all five stable isotopes of germanium are studied. The isotopic shift of absorption bands in the IR region, caused by phonon phenomena, which was discovered by the authors for the first time, is considered.

Working Voltage Switching the Photo-/Thermo-Electric Effect for Distinct Ultraviolet and Infrared Signal Detection.

The combination of sensing invisible ultraviolet photons and infrared radiation can significantly enhance target recognition by offsetting their own limit in a short sensing range and poor spatial resolution. However, the difference in their wavelength sets unique requirements for sensing materials and devices, which makes it hard to establish their implementation in a single detector. In this work, we present the design of a single detector with CH3NH3PbCl3 (MAPbCl3) for distinguishing ultraviolet and IR signals by switching its operating mode in the photo-/thermo-electric effect. The large optical band gap of ∼3.2 eV in MAPbCl3 ensures the response toward an ultraviolet photon, while its efficient thermoelectric effect allows the sensing of an IR signal. As a result, the detector exhibits a specific detectivity of 4.5 × 1012 Jones for 395 nm ultraviolet photons under 0 V, while under the working voltage of 2.5 V, it demonstrates a superior temperature coefficient of resistance of -3.7% K-1, a specific detectivity of 4.8 × 108 Jones, and a limit of detection of 0.58 mW/cm2 for 4 μm photons. The functionality of the switching response to ultraviolet or IR photons by working voltage allows background subtraction and enhances the target discrimination in the imaging.

The role of greenhouse gases in radiative equilibrium – Thermodynamic evaluation

Abstract The significance of greenhouse gases for climate change is assessed in the case of carbon dioxide on the basis of thermodynamic data. According to the values of the molar heat capacity, no increased heat-storing property of this greenhouse gas can be determined. The absorption and desorption of infrared radiation by the greenhouse gases is seen as a reversible dynamic process, which on the one hand reduces the IR radiation from the Sun, and on the other hand, delays the re-radiation from the Earth. As converters of heat into IR photons and vice versa, the greenhouse gases play an important role in balancing the radiation. The direction of heat transport in the atmosphere is determined by the 2nd Law of Thermodynamics. The range of IR radiation is determined according to the gradation of air pressure in the atmosphere.

Methane sensing in the mid-IR using short wave IR photon counting detectors via non-linear interferometry

We demonstrate a novel MIR methane sensor shifting measurement wavelength to SWIR (1.55μm) by using non-linear interferometry. The technique exploits the interference effects seen in three-wave mixing when pump, signal, and idler modes make a double pass through a nonlinear crystal. The method allows sensing at wavelengths where detectors are poor (>3μm) and detection at wavelengths where photon counting sensitivity can be achieved. In a first experimental demonstration, we measured a small methane concentration inside a gas cell with high precision. This interferometer can be built in a compact design for field operations and potentially enable the detection of low concentrations of methane at up to 100m range. Signal-to-noise ratio calculations show that the method can outperform existing short wavelength (∼1.65μm) integrated path differential absorption direct sensing at high (>10−4) non-linear gain.

Characterization of the Phonon Sensor of the CRYOSEL Detector with IR Photons

Characterization of the Phonon Sensor of the CRYOSEL Detector with IR Photons

Gamma-ray variability and multi-wavelength insights into the unprecedented outburst from 4C 31.03

The blazar 4C31.03 recently underwent a major γ-ray outburst at the beginning of 2023 after a prolonged quiescent phase. Fermi-LAT reported a daily average flux of 5×10−6 phs cm−2 s−1, which is about 60 times its average value. We investigated this extraordinary outbreak through temporal and multi-wavelength analysis. From the statistical analysis of the γ-ray lightcurves using Bayesian blocks, we identified 3 epochs of prominent flares. The fastest flux decay during this major outburst was observed within 5.5±0.7 hours. The highest energy of γ-ray photons found from the source during the active phase is ∼82GeV. Using the transparency of γ-rays against pair production and light crossing time argument, we could obtain the minimum jet Doppler factor as 17 corresponding to the flaring state. The broadband spectral energy distribution study performed using synchrotron, SSC and EC emission processes supports the external Compton scattering of IR photons as the likely mechanism for the γ-ray emission from the source. The results of this study support the scenario of the emission region in 4C31.03, being located beyond the Broad line region from the central blackhole. The long-term γ-ray flux distribution depicts a double log-normal variability, indicating that two distinct flux states are active in this energy band. The index distribution also reveals a two distinct variability pattern and hints that the γ-ray spectrum can be more precisely described by two photon indices.

Enhancing Performance in P3HT:ICBA Organic Photovoltaics through IR Photon Harvesting with DIBSq Squaraine Dye

Enhancing Performance in P3HT:ICBA Organic Photovoltaics through IR Photon Harvesting with DIBSq Squaraine Dye

Monolithic Two-Terminal Tandem Solar Cells Using Sb2S3 and Solution-Processed PbS Quantum Dots Achieving an Open-Circuit Potential beyond 1.1 V.

Multijunction solar cells have the prospect of a greater theoretical efficiency limit than single-junction solar cells by minimizing the transmissive and thermalization losses a single absorber material has. In solar cell applications, Sb2S3 is considered an attractive absorber due to its elemental abundance, stability, and high absorption coefficient in the visible range of the solar spectrum, yet with a band gap of 1.7 eV, it is transmissive for near-IR and IR photons. Using it as the top cell (the cell where light is first incident) in a two-terminal tandem architecture in combination with a bottom cell (the cell where light arrives second) of PbS quantum dots (QDs), which have an adjustable band gap suitable for absorbing longer wavelengths, is a promising approach to harvest the solar spectrum more effectively. In this work, these two subcells are monolithically fabricated and connected in series by a poly(3,4-ethylene-dioxythiophene) polystyrene sulfonate (PEDOT:PSS)-ZnO tunnel junction as the recombination layer. We explore the surface morphology of ZnO QD films with different spin-coating conditions, which serve as the PbS QD cell's electron transport material. Furthermore, we examine the differences in photogenerated current upon varying the PbS QD absorber layer thickness and the electrical and optical characteristics of the tandem with respect to the stand-alone reference cells. This tandem architecture demonstrates an extended spectral response into the IR with an open-circuit potential exceeding 1.1 V and a power conversion efficiency of 5.6%, which is greater than that of each single-junction cell.

Large-area polycrystalline α-MoO3 thin films for IR photonics

In recent years, the excitation of surface phonon polaritons (SPhPs) in van der Waals materials received wide attention from the nanophotonics community. Alpha-phase Molybdenum trioxide (α-MoO3), a naturally occurring biaxial hyperbolic crystal, emerged as a promising polaritonic material due to its ability to support SPhPs for three orthogonal directions at different wavelength bands (range 10–20 μm). Here, we report on the fabrication, structural, morphological, and optical IR characterization of large-area (over 1 cm2 size) α-MoO3 polycrystalline film deposited on fused silica substrates by pulsed laser deposition. Due to the random grain distribution, the thin film does not display any optical anisotropy at normal incidence. However, the proposed fabrication method allows us to achieve a single α-phase, preserving the typical strong dispersion related to the phononic response of α-MoO3 flakes. Remarkable spectral properties of interest for IR photonics applications are reported. For instance, a polarization-tunable reflection peak at 1006 cm−1 with a dynamic range of ΔR = 0.3 and a resonance Q-factor as high as 53 is observed at 45° angle of incidence. Additionally, we report the fulfillment of an impedance matching condition with the SiO2 substrate leading to a polarization-independent almost perfect absorption condition (R < 0.01) at 972 cm−1 which is maintained for a broad angle of incidence. In this framework our findings appear extremely promising for the further development of mid-IR lithography-free, scalable films, for efficient and large-scale sensors, filters, thermal emitters, and label-free biochemical sensing devices operating in the free space, using far-field detection setups.

Vibrational spectroscopy and dissociation dynamics of cyclohexyl hydroperoxide.

Organic hydroperoxides (ROOH) are ubiquitous in the atmospheric oxidation of volatile organic compounds (VOCs) as well as in low-temperature oxidation of hydrocarbon fuels. The present work focuses on a prototypical cyclic hydroperoxide, cyclohexyl hydroperoxide (CHHP). The overtone OH stretch (2νOH) spectrum of jet-cooled CHHP is recorded by IR multiphoton excitation with UV laser-induced fluorescence detection of the resulting OH products. A distinctive IR feature is observed at 7012.5 cm-1. Two conformers of CHHP are predicted to have similar stabilities (within 0.2 kcal mol-1) and overtone OH stretch transitions (2νOH), yet are separated by a significant interconversion barrier. The IR power dependence indicates that absorption of three or more IR photons is required for dissociation of CHHP to cyclohexoxy (RO) and OH radical products. Accompanying high-level single- and multi-reference electronic structure calculations quantitatively support the experimental results. Calculations are extended to a range of organic hydroperoxides to examine trends in bond dissociation energies associated with RO + OH formation and compared with prior theoretical results.

Operando IR Optical Control of Localized Charge Carriers in BiVO4 Photoanodes.

In photoelectrochemical cells (PECs) the photon-to-current conversion efficiency is often governed by carrier transport. Most metal oxides used in PECs exhibit thermally activated transport due to charge localization via the formation of polarons or the interaction with defects. This impacts catalysis by restricting the charge accumulation and extraction. To overcome this transport bottleneck nanostructuring, selective doping and photothermal treatments have been employed. Here we demonstrate an alternative approach capable of directly activating localized carriers in bismuth vanadate (BiVO4). We show that IR photons can optically excite localized charges, modulate their kinetics, and enhance the PEC current. Moreover, we track carriers bound to oxygen vacancies and expose their ∼10 ns charge localization, followed by ∼60 μs transport-assisted trapping. Critically, we demonstrate that localization is strongly dependent on the electric field within the device. While optical modulation has still a limited impact on overall PEC performance, we argue it offers a path to control devices on demand and uncover defect-related photophysics.

Harnessing of low-energy IR photons via oxygen-vacancies in SrTiO3 nanocrystals for photocatalytic hydrogen production

The surface-oxygen vacancies were generated to enhance the near-IR light response of the SrTiO3 photocatalyst by heating SrTiO3 in a highly reducing environment. The UV–visible diffuse reflectance spectra of SrTiO3-Ov revealed strong absorption between 400 and 800 nm, while IPCE response was extended beyond 800 nm, confirming the near-IR light response of SrTiO3-Ov. The hydrogen production rates for SrTiO3-Ov at pH 3.0 under full solar spectrum, visible and IR radiation were 100, 25 and 10 μlg−1h−1, respectively. The respective normalized hydrogen with respect to light intensity were found to be 100, 50 and 33 μlg−1h−1 while hydrogen production of pristine SrTiO3 was less than 2 μlg−1h−1 under full solar spectrum. The mid-gap Ov and Ti3+ states in SrTiO3-Ov are key factors in the origin of the near-IR responses of the catalyst and the feasibility of using low-photonic-energy IR light to produce hydrogen by water splitting was demonstrated.

Studies on chalcogenide glass solution-processed films towards IR photonics applications

Chalcogenide glasses are promising infrared materials because of their notable physical, optical, electrical, and thermal properties. Solution-processed chalcogenide glass films are highly desirable since they can retain the properties of parent glass and can be used as a platform for various integrated photonic applications. This work is intended to optimize the annealing conditions for effective solvent removal and to evaluate the influence of annealing on the morphological, compositional, structural, and optical properties of EDA-processed Ge-Sb-Se drop-cast glass films.

The Origin of High-energy Emission in the Young Radio Source PKS 1718–649

We present a model for the broadband radio-to-γ-ray spectral energy distribution of the compact radio source PKS 1718–649. Because of its young age (≃100 yr) and proximity (z = 0.014), PKS 1718–649 offers a unique opportunity to study the nuclear conditions and the jet/host galaxy feedback process at the time of the initial radio jet expansion. PKS 1718–649 is one of a handful of young radio jets with γ-ray emission that has been confirmed by the Fermi/LAT detector. We show that in PKS1718−649 this γ-ray emission can be successfully explained by Inverse Compton scattering of the UV photons, presumably from an accretion flow, off nonthermal electrons in the expanding radio lobes. The origin of the X-ray emission in PKS 1718–649 is more elusive. While Inverse Compton scattering of the IR photons emitted by a cold gas in the vicinity of the expanding radio lobes contributes significantly to the X-ray luminosity, the data require an additional source of X-rays, e.g., a weak X-ray corona or a radiatively inefficient accretion flow, as expected from a LINER-type nucleus, such as that of PKS 1718–649. We find that the jet in PKS 1718–649 has low power, L j ≃ 2 × 1042 erg s−1, and expands in an environment with density n 0 ≃ 3–20 cm−3. The inferred mass accretion rate and gas mass reservoir within 50–100 pc of the galactic center are consistent with estimates from the literature obtained by tracing molecular gas in the innermost region of the host galaxy with SINFONI and the Atacama Large Millimeter/submillimeter Array.

Advantages of the frequency-conversion technique in quantum interference

Hong-Ou-Mandel (HOM) interference is a key phenomenon for understanding quantum interference and a basic tool for quantum information and metrological applications. By introducing the nonlinear frequency-conversion (NFC) technique into HOM interferometers, more phenomena could be found and more functions could be developed. Here, tunable quantum spatial beating is observed in a HOM interferometer based on the postfilter scheme, where two NFC modules function as tunable band-pass filters. Degenerate IR photon pairs at 1079.00 nm are generated based on the noncritical phase-matching spontaneous parametric down-conversion process and are up-converted to the visible band around 633.40 nm by the NFC modules before the detectors. We show that in addition to the filtering effect, the NFC can also improve the photon detection efficiency based on silicon avalanched detector, increasing the coherence length, and therefore improving the heralding efficiency and visibility. Our results demonstrate the advantages of the NFC technique in HOM interference, which could also be generalized to other quantum interference.

Analysis of RABITT time delays using the stationary multiphoton molecular R -matrix approach

We employ the recently developed multiphoton $R$-matrix method for molecular above-threshold photoionization to obtain second-order ionization amplitudes that govern the interference in RABITT experiments. This allows us to extract RABITT time delays that are in better agreement with nonperturbative time-dependent simulations of this process than the typically used combination of first-order (Wigner) delays and asymptotic corrections. We calculate molecular-frame as well as orientation-averaged RABITT delays for ${\mathrm{H}}_{2}, {\mathrm{N}}_{2}, {\mathrm{CO}}_{2}, {\mathrm{H}}_{2}\mathrm{O}$, and ${\mathrm{N}}_{2}\mathrm{O}$ and analyze the origin of various structures in the time delays including the effects of partial-wave interference, shape resonances, and orientation averaging. Time delays for B and C states of ${\mathrm{CO}}_{2}{}^{+}$ are strongly affected by absorption of the second (IR) photon in the ion. This effect corresponds to an additional contribution ${\ensuremath{\tau}}_{\text{coupl}}$ to the asymptotic approximation for the RABITT delays $\ensuremath{\tau}\ensuremath{\approx}{\ensuremath{\tau}}_{\text{mol}}+{\ensuremath{\tau}}_{cc}+{\ensuremath{\tau}}_{\text{coupl}}$. Applicability of the asymptotic theory depends on the target and IR photon energy but typically starts at approximately 30--35 eV of XUV photon energy.

Long-term multi-wavelength study of temporal and spectral properties of 3C 279

We present a long-term multi-wavelength study of the flat spectrum radio quasar 3C 279 using near simultaneous observations available from July 01, 2012 and June 31, 2018 (MJD 56109-58301). The data set includes measurements from the TACTIC, Fermi-LAT, Swift-XRT, Swift-UVOT, SMARTS, Steward-SPOL, and OVRO. The TACTIC telescope has monitored the source 3C 279 for ∼ 70 h between 2013 and 2018 in the energy range of > 0.85 TeV and yields null result. We have analysed the Fermi-LAT data to obtain the 5-day binned light curve in the energy range 0.1–300 GeV. One low and six high emission states are identified in the Fermi-LAT light curve. The high emission states are modelled with an exponential rise and decay time profile using 1-day averaged flux points and have been characterized as the asymmetric flares. The spectral analysis of near simultaneous X-ray and γ-ray data from the Swift-XRT and Fermi-LAT respectively indicates harder when brighter trend during the high activity states. The time averaged broadband spectral energy distributions corresponding to the seven states are successfully reproduced under the framework of a simple one zone leptonic emission model with IR photons originating from the dusty torus as the dominant target for the inverse Compton scattering by the relativistic electrons. Results obtained from the broadband modelling suggest that the non-thermal emission region in the jet is above the broadline region. This is also supported by the average value of seed factor estimated using the derived model parameters. A positive correlation between the bulk Lorentz factor of the emission zone and average γ-ray flux measurements for each state indicates that an increase in the bulk Lorentz factor can be the dominant cause for the observed flares from 3C 279. We also discuss the implications of the obtained model parameters in detail to understand the long-term behaviour of the source.

Infrared Photoactivation Boosts Reporter Ion Yield in Isobaric Tagging.

Isobaric tagging facilitates multiplexed experiments that can determine sequences and relative amounts of peptides in biological samples using tandem mass spectrometry (MSn). Limited reporter ion generation limits quantitative accuracy and precision. As reporter ions are susceptible to unintended fragmentation and scattering by high-energy collisions, we activated peptides with IR photons and prevented successive dissociation of generated reporter ions with ion parking, which altogether boosted reporter ion yield by up to 55%. Even so, unintended co-isolation of contaminating peaks in MS2 experiments distorts reporter ion intensities and can distort quantitative information. MS3 experiments address contamination by generating reporter ions via collisional activation (HCD) of one or more peptide product ions rather than the isolated peptide precursor ion. Because HCD performance is related to m/z, activation of multiple synchronously isolated product ions generates less than optimal reporter ion intensities. In this work, we show that using infrared multiphoton dissociation, which is not dependent on m/z, to generate reporter ions from 10 synchronously isolated peptide product ions results in a 2.4-fold increase in reporter ion intensities, significantly enhancing the sensitivity and dynamic range of quantitation via isobaric tagging.

Broadband wavelength-selective isotype heterojunction n+-ZnO/n-Si photodetector with variable polarity

Αn isotype heterojunction n+-ZnO/n-Si photodetector is developed, demonstrating wavelength-selective or broadband operation, depending on the applied bias voltage. Additionally, at self-powered (zero bias) operation, it distinguishes between UV, visible, and near IR (NIR) photons by polarity control of the photocurrent. The photodetector is developed by atomic layer deposition (ALD) of ZnO on n-Si, followed by electric contact deposition and annealing. Photoluminescence measurements reveal high optical quality and improved crystallinity of annealed ZnO on silicon. Photocurrent measurements as a function of illumination wavelength and bias voltage show small negative values in the UV–visible spectral range at zero and positive bias voltage and high positive values in the NIR spectral range. For these measurements, we consider the electric contact to ZnO as the anode and the electric contact to silicon as the cathode. At negative bias voltage, the device shows broadband operation with high photocurrent values across the UV–vis-NIR.

Transparent fluoride glass-ceramics with phase-selective crystallization for middle IR photonics

We fabricate transparent fluoroindate glass-ceramics with phase-selective crystallization (SrF2, CaF2 and MgF2) using a general one-step strategy. The ab initio molecular dynamics provide fundamental insights into phase-separation at the atomic scale.