Infrared Wavelength Range Research Articles

Effect of sequence built on photonic band gap properties of one-dimensional quasi-periodic photonic crystals: Application to Thue-Morse and Double-period structures

We elaborated by Radio frequency magnetron sputtering two types of one-dimensional quasi-periodic photonic crystals, based on Si/SiO2 materials, according to the Thue-Morse sequence and the Double-period one. We have investigated their optical properties, throughout the reflection transmission spectra, experimentally as well theoretically by using the transfer matrix method. The experimental spectra of these two structures are performed at normal incident light configuration, in the near infrared wavelengths range, and, are compared for the same number of layers, for a generation number N varying from 0 to 5, corresponding to a number of layers varying from 1 to 32, respectively. We experimentally put in evidence the appearance of photonic band gaps for N higher than 2, which are then well defined for N equal to 4, for the two structures. Furthermore, the results show that these two quasi-periodic structures exhibit sharp localized modes of light within the photonic band gaps, covering the optical telecommunication wavelengths 1.33 and 1.55 μm, with different number and position depending, on the built in distribution structures. The results also show a good agreement between the experimental and calculated spectra.

(Invited) Photoluminescnece Brightening in Single Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWNTs) are fundamentally interesting and technologically relevant materials with size tunable absorption and emission across a range of visible and near infrared wavelengths. However, several important aspects of their photophysical properties are not known in enough depth to predict how SWNTs will behave as part of larger integrated nanosystems. In particular, simple concepts such as the fundamental factors that affect photoluminescence efficiency (PL QY) are not well understood for SWNTs. We recently found that for DNA-wrapped SWNTS, the SWNT PL QY can be increased substantially in the presence of small amounts of mildly reducing molecules such as dithiothreitol (DTT) and Trolox. We will present comprehensive studies of the molecular-induced changes in PL from SWNTs suspended in several other commonly used surfactants. For example, upon addition of the reducing agents, sodium dodecyl sulfate (SDS) wrapped SWNTs showed a 4-fold PL intensity increase while sodium cholate (SC) wrapped SWNTs showed PL decrease by ~45%. Minimal change in PL was observed for SWNTs dispersed in sodium dodecylbenzene sulfonate (SDBS) and sodium deoxycholate (DOC). By using a state-of-the art NIR sensitive APD, we were able to acquire time resolved PL data from each sample. For SWNTs that were brightened (darkened), the non-radiative rate decreased (increased) and the radiative rate increased (decreased). Our preliminary conclusion is that adding the reductants causes a change in the molecular structure of the surfactant on the SWNT, which changes the local dielectric constant as well as the interaction of the exciton with the molecular orbitals of the surfactant. We will also present recent data on the PL brightening of individual SDS wrapped SWNTs, whereby we found the PL efficiency enhancement varied substantially among individual nanotubes, with some brightening by up to 6.5 times while others brightened by only 16%. Studies of NTs longer than the diffraction limit reveal the surprising finding that upon adding the reductants, the NTs brightened uniformly, as determined from the PL image. Since non-uniform brightening would result from consecutive interactions with individual point defects, the observation of uniform PL brightening is consistent with the interpretation that the reductants are causing changes in the local SWNT environment. Further, single step brightening across the entire NT followed by a constant, nonblinking PL level suggests the brightening effect could be due to as little as a single molecule interacting with the NT.

Light Induced Electron-Phonon Scattering Mediated Resistive Switching in Nanostructured Nb Thin Film Superconductor

abstractThe elemental Nb is mainly investigated for its eminent superconducting properties. In contrary, we report of a relatively unexplored property, namely, its superior optoelectronic property in reduced dimension. We demonstrate here that nanostructured Nb thin films (NNFs), under optical illumination, behave as room temperature photo-switches and exhibit bolometric features below its superconducting critical temperature. Both photo-switch and superconducting bolometric behavior are monitored by its resistance change with light in visible and near infrared (NIR) wavelength range. Unlike the conventional photodetectors, the NNF devices switch to higher resistive states with light and the corresponding resistivity change is studied with thickness and grain size variations. At low temperature in its superconducting state, the light exposure shifts the superconducting transition towards lower temperature. The room temperature photon sensing nature of the NNF is explained by the photon assisted electron-phonon scattering mechanism while the low temperature light response is mainly related to the heat generation which essentially changes the effective temperature for the device and the device is capable of sensing a temperature difference of few tens of milli-kelvins. The observed photo-response on the transport properties of NNFs can be very important for future superconducting photon detectors, bolometers and phase slip based device applications.

Morphology Control of Ag Polyhedron Nanoparticles for Cost‐Effective and Fast Solar Steam Generation

Since introduction of inorganic metallic salt serves as an inducer for modulating crystalline nucleation and overgrowth, we have synthesized highly monodispersed silver nanoparticles (AgNPs) (diameter: 48.7–411.9 nm) in the shape of polyhedral quasi‐spheres via a household microwave oven. The localized surface plasmon resonance (LSPR) absorption spectrum of AgNPs exhibits a good match to the solar spectrum in the UV to near infrared wavelength range. Consequently, AgNPs dispersed in deionized (DI) water have a great potential for efficient solar heat collecting, able to convert both hot steam and its clustering nanobubbles into macro‐bubbles (macroscopic bubbles) in a fast and consecutive manner. The maximum values of solar thermal conversion efficiency, rate of steam, and diameter of the clustered macroscopic bubbles obtained in the preliminary experiments under the best conditions are 82.45%, 16.8 g/(AM1.5 · m2 · min), and 2.4 cm, respectively. Here we show that the designated system has fast dynamics of steam generation, as well as easy and cost‐effective scale‐up capability, suggesting that the steam generation system using AgNPs might be feasible after further development.

Coupling coefficients of different disk microresonators with whispering gallery modes

The coupling coefficients of the disk microresonators consisting of different dielectrics are presented. The analytical expressions for the coupling coefficients are obtained. The basic regularities of the coupling coefficient changing on the structure parameter variations are considered. The coupling coefficients as functions of main structure parameters are studied. The calculation results of the transmission coefficients as well as the reflection coefficients of the bandpass filters building up on different disk microresonators with different modes are presented. The S-matrix frequency dependences of the bandpass filters on different disk microresonators in the infrared wavelength range are calculated. The necessary for acceptable measure of the scattering dielectric Q-factor values are determined. The amplitude-frequency characteristics of the bandpass filters on the vertically coupled as well as laterally coupled disc microresonators are investigated. Most optimal configurations of coupled microresonators allowing to achieve the best scattering characteristics are determined. It's shown that using of microresonators with whispering gallery modes relatively easy allows to obtain frequency-symmetrical characteristics of the filters.

Low-bandgap mixed tin–lead iodide perovskite absorbers with long carrier lifetimes for all-perovskite tandem solar cells

Tandem solar cells using only metal-halide perovskite sub-cells are an attractive choice for next-generation solar cells. However, the progress in developing efficient all-perovskite tandem solar cells has been hindered by the lack of high-performance low-bandgap perovskite solar cells. Here, we report efficient mixed tin–lead iodide low-bandgap (∼1.25 eV) perovskite solar cells with open-circuit voltages up to 0.85 V and over 70% external quantum efficiencies in the infrared wavelength range of 700–900 nm, delivering a short-circuit current density of over 29 mA cm−2 and demonstrating suitability for bottom-cell applications in all-perovskite tandem solar cells. Our low-bandgap perovskite solar cells achieve a maximum power conversion efficiency of 17.6% and a certified efficiency of 17.01% with a negligible current–voltage hysteresis. When mechanically stacked with a ∼1.58 eV bandgap perovskite top cell, our best all-perovskite 4-terminal tandem solar cell shows a steady-state efficiency of 21.0%. All-perovskite tandem solar cells hold the promise of high efficiencies whilst safeguarding the ease of fabrication intrinsic to perovskites. Here, Zhao et al. present a certified 17% efficient tin and lead perovskite solar cell, which is integrated as the low-bandgap component of a tandem device with 21% efficiency.

H2 sensor based on tapered optical fiber coated with MnO2 nanostructures

A novel hydrogen (H2) sensor was developed using optical fiber coated with manganese dioxide (MnO2) nanostructures. Optical multimode fiber (MMF) of 125μm in diameter as the transducing platform was tapered to 20μm to enhance the evanescent field of the light propagates in the fiber core. The tapered fiber was coated with MnO2 nanograins synthesised via chemical bath deposition (CBD) process. Catalytic Palladium (Pd) was sputtered onto the MnO2 layer to improve the H2 detection. The sensing layer was characterized through Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD) and Raman Spectroscopy to verify the properties of MnO2. Two sets of sensors consist of as-prepared MnO2 and 200°C annealed MnO2 were tested towards H2 gas. The tapered optical fiber coated with Pd/MnO2 nanograins was found to be sensitive towards H2 with different concentrations in synthetic air at 240°C operating temperature. The annealed sensor showed higher response and sensitivity as compared to the as-prepared sensors when measured in the visible to near infra-red optical wavelength range. The absorbance response of the annealed Pd/MnO2 on fiber has increased to 65% as compared to 20% for the as-prepared Pd/MnO2 upon exposure to 1% H2 in synthetic air.

III-V semiconductor extended short-wave infrared detectors

The extended-shortwave infrared wavelength range, encompassing wavelengths from 2.2 to 3 μm, is significantly underdeveloped when compared to the shortwave and midwave infrared bands. Achieving high performance detectors in the extended-shortwave range is desirable; however, it is unclear whether to approach the wavelength range via the detector structures and materials common to the shortwave regime or those common to the midwave regime. Both approaches are studied here. Electrical and optical characteristics of conventional photodiodes and nBn architecture detectors with 2.8 μm cutoff wavelengths are analyzed for detectors with both lattice-mismatched InGaAs and lattice-matched InGaAsSb absorbing regions. Regardless of the absorber material, the nBn detectors show nearly 3 orders of magnitude improvements in performance over the conventional photodiode architecture, and the lattice-matched InGaAsSb nBn exhibits a further reduction in the dark current by more than an order of magnitude when compared to the lattice-mismatched InGaAs nBn. The InGaAsSb nBn exhibits high quality optical detection resulting in a high performance detector in the extended-shortwave infrared band.

Mid-IR colloidal quantum dot detectors enhanced by optical nano-antennas

We report the fabrication of a colloidal quantum dot based photodetector designed for the 3–5 μm mid infrared wavelength range incorporated with optical nano-antenna arrays to enhance the photocurrent. The fabricated arrays exhibit a resonant behavior dependent on the length of the nano-antenna rods, in good agreement with numerical simulation. The device exhibits a three-fold increase in the spectral photoresponse compared to a photodetector device without antennas, and the resonance is polarized parallel to the antenna orientation. We numerically estimate the device quantum efficiency and investigate its bias dependence.

Refractory material based frequency selective emitters/absorbers for high efficiency and thermal stable thermophotovoltaics

Refractory materials based frequency selective emission/absorption is extremely encouraging for various applications, especially the combustion based thermophotovoltaics (TPV) and solar-TPV systems. The frequency selective emitters/absorbers also face the challenges of robust operation at elevated temperatures. Here, we report titanium nitride based thermal stable emitters/absorbers with good selectivity in the near infrared wavelength range. The titanium nitride nanocavitity array provides high emissivity/absorptivity at the desired short wavelength range but suppressed emissivity/absorptivity at the long wavelength range, and this design could be used to obtain high power density of the TPV system. The cut-off wavelength could be adjusted by encapsulating the cavities with different dielectrics. Meanwhile, the encapsulating layer protects the nanocavity structure from deformation at high temperatures. The thermal stability at 1073 K and 1273 K for two hours in Argon was demonstrated for the encapsulated nanocavity structure.

Highly transparent conductive AZO/Zr50Cu50/AZO films in wide range of visible and near infrared wavelength grown by pulsed laser deposition

Novel AZO/Zr50Cu50/AZO tri-layer transparent conductive films with excellent transmittance in both visible and near infrared region were successfully prepared by pulsed laser deposition on glass substrates. The electrical and optical properties were investigated at various Zr50Cu50 thicknesses. As the AZO thickness was fixed at 50nm and Zr50Cu50 thickness was varied between 1 and 18nm, it was found that AZO (50nm)/Zr50Cu50/AZO (50nm) tri-layer films exhibited good conductivity and high transmittance in both visible and near infrared wavelength. Additionally, both the electrical and optical properties of AZO (50nm)/Zr50Cu50 (2nm)/AZO (50nm) tri-layer films were found to be sensitive to the growth temperature. In this work, the lowest sheet resistance (43Ω/□) and relatively high transmittance (∼80%) in the range of 400–2000nm were achieved while the growth temperature was 350°C. Furthermore, the AZO (50nm)/Zr50Cu50 (2nm)/AZO (50nm) thin film deposited at 350°C exhibits the highest figure of merit of 1.42×10−3Ω−1, indicating that the multilayer is promising for coated glasses and thin film solar cells.

Tunable metamaterial-induced transparency with gate-controlled on-chip graphene metasurface.

We propose and numerically investigate a gate-controlled on-chip graphene metasurface consisting of a monolayer graphene sheet and silicon photonic crystal-like substrate, to achieve an electrically-tunable induced transparency. The operation mechanism of the induced transparency of the on-chip graphene metasurface is analyzed. The tunable optical properties with different gate-voltages and polarizations have been discussed. Additionally, the spectral feature of the on-chip graphene metasurface as a function of the refractive index of the local environment is also investigated. The result shows that the on-chip graphene metasurface as a refractive index sensor can achieve an overall figure of merit of 8.89 in infrared wavelength range. Our study suggests that the proposed structure is potentially attractive as optoelectronic modulators and refractive index sensors.

Aerogel volatiles concentrator and analyzer (AVCA) – Collection and concentration of trace volatile organics in aerogel for spectroscopic detection

A study was conducted to determine the efficacy of using silica aerogel to collect and concentrate ambient trace organics for spectroscopic analysis. Silica aerogel was exposed to atmospheres containing trace amounts of polycyclic aromatic and aliphatic hydrocarbons. The organics present were concentrated in the aerogels by factors varying from 10 to more than 1000 over the levels found in the atmospheres, depending on the specific organic present. Since silica aerogel is transparent over a wide range of optical and near infrared wavelengths, UV-induced fluorescence, Raman and infrared spectroscopies were used to detect and identify the organics collected by the aerogel. Measurements were conducted to determine the sensitivity of these spectroscopic methods for determining organics concentrated by aerogels and the effectiveness of this method for identifying systems containing multiple organic species. Polycyclic aromatic hydrocarbons (PAHs) were added to simulated Mars regolith and then vaporized by modest heating in the presence of aerogel. The aerogels adsorbed and concentrated the PAHs, which were detected by induced fluorescence and Raman and FTIR spectroscopies.

Daniel K. Inouye Solar Telescope: High‐resolution observing of the dynamic Sun

AbstractThe 4‐m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly known as the Advanced Technology Solar Telescope (ATST) is currently under construction on Haleakalā (Maui, Hawai'i) projected to start operations in 2019. At the time of completion, DKIST will be the largest ground‐based solar telescope providing unprecedented resolution and photon collecting power. The DKIST will be equipped with a set of first‐light facility‐class instruments offering unique imaging, spectroscopic and spectropolarimetric observing opportunities covering the visible to infrared wavelength range. This first‐light instrumentation suite will include: a Visible Broadband Imager (VBI) for high‐spatial and ‐temporal resolution imaging of the solar atmosphere; a Visible Spectro‐Polarimeter (ViSP) for sensitive and accurate multi‐line spectropolarimetry; a Fabry‐Pérot based Visible Tunable Filter (VTF) for high‐spatial resolution spectropolarimetry; a fiber‐fed Diffraction‐Limited Near Infra‐Red Spectro‐Polarimeter (DL‐NIRSP) for two‐dimensional high‐spatial resolution spectropolarimetry (simultaneous spatial and spectral information); and a Cryogenic Near Infra‐Red Spectro‐Polarimeter (Cryo‐NIRSP) for coronal magnetic field measurements and on‐disk observations of, e.g., the CO lines at 4.7 μm. We will provide an overview of the DKISTs unique capabilities with strong focus on the first‐light instrumentation suite, highlight some of the additional properties supporting observations of transient and dynamic solar phenomena, and touch on some operational strategies and the DKIST critical science plan. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of the Effect of near Infrared Spectrometer Wavelength Range and Calibration Algorithms on Prediction of Crushing Strength of Pharmaceutical Tablets

This study was aimed at understanding the effect of near infrared (NIR) spectrometer wavelength range and calibration approaches on the performance of pharmaceutical tablet crushing strength prediction methods. The study utilised a six-component tablet formulation, created with variability in excipient ratio and compression force. Method development was tested with two NIR spectrometers and three calibration approaches: spectral slope, partial least squares (PLS) and multiple linear regression (MLR). The sensors used in the study were based on diffuse reflectance sensing geometry with wavelength ranges of 1100–2498 nm and 1350–1800 nm. The three calibration approaches demonstrated an improved prediction of crushing strength with the longer wavelength range, indicative of its significant impact on method performance. It was established that the PLS approach reduced the impact of wavelength range on performance by maximising the covariance between crushing strength and the spectral features associated with baseline shift/slope change and excipient ratio. The MLR approach incorporated variables of physical/chemical nature to mitigate risks to method performance.

Device-level vacuum packaged uncooled microbolometer on a polyimide substrate

Uncooled infrared detectors (IR) on a polyimide substrate have been demonstrated where amorphous silicon (a-Si) was used as the thermometer material. New concepts in uncooled microbolometers were implemented during the design and fabrication, such as the integration of a germanium long-pass optical filter with the device-level vacuum package and a double layer absorber structure. Polyimide was used for this preliminary work towards vacuum-packaged flexible microbolometers. The detectors were fabricated utilizing a carrier wafer and low adhesion strength release layer to hold the flexible polyimide substrate during fabrication in order to increase the release yield. The IR detectors showed a maximum detectivity of 4.54×106cmHz1/2/W at a 4Hz chopper frequency and a minimum noise equivalent power (NEP) of 7.72×10−10W/Hz1/2 at a biasing power of 5.71pW measured over the infrared wavelength range of 8–14μm for a 35μm×35μm detector. These values are comparable to other flexible microbolometers with device-level vacuum packaging which are found in literature.

Standoff Mechanical Resonance Spectroscopy Based on Infrared-Sensitive Hydrogel Microcantilevers.

This paper reports a highly sensitive and selective remote chemical sensing platform for surface-adsorbed trace chemicals by using infrared (IR)-sensitive hydrogel microcantilevers. Poly(ethylene glycol) diacrylate (PEG-DA) hydrogel microcantilevers are fabricated by ultraviolet (UV) curing of PEG-DA prepolymer introduced into a poly(dimethylsiloxane) mold. The resonance frequency of a PEG-DA microcantilever exhibits high thermal sensitivity due to IR irradiation/absorption. When a tunable IR laser beam is reflected off a surface coated with target chemical onto a PEG-DA microcantilever, the resonance frequency of the cantilever shifts in proportion to the chemical nature of the target molecules. Dynamic responses of the PEG-DA microcantilever can be obtained in a range of IR wavelengths using a tunable quantum cascade laser that can form the basis for the standoff mechanical resonance spectroscopy (SMRS). Using this SMRS technique, we have selectively detected three compounds, dimethyl methyl phosphonate (DMMP), cyclotrimethylene trinitramine (RDX), and pentaerythritol tetranitrate (PETN), located 4 m away from the PEG-DA microcantilever detector. The experimentally measured limit of detection for PETN trace using the PEG-DA microcantilever was 40 ng/cm2. Overall, the PEG-DA microcantilever is a promising candidate for further exploration and optimization of standoff detection methods.

Eye tracking under dichoptic viewing conditions: a practical solution.

In several research contexts it is important to obtain eye-tracking measures while presenting visual stimuli independently to each of the two eyes (dichoptic stimulation). However, the hardware that allows dichoptic viewing, such as mirrors, often interferes with high-quality eye tracking, especially when using a video-based eye tracker. Here we detail an approach to combining mirror-based dichoptic stimulation with video-based eye tracking, centered on the fact that some mirrors, although they reflect visible light, are selectively transparent to the infrared wavelength range in which eye trackers record their signal. Although the method we propose is straightforward, affordable (on the order of US$1,000) and easy to implement, for many purposes it makes for an improvement over existing methods, which tend to require specialized equipment and often compromise on the quality of the visual stimulus and/or the eye tracking signal. The proposed method is compatible with standard display screens and eye trackers, and poses no additional limitations on the quality or nature of the stimulus presented or the data obtained. We include an evaluation of the quality of eye tracking data obtained using our method, and a practical guide to building a specific version of the setup used in our laboratories.

Optical characterization and modelling of paint top-coatings for low-emittance applications

The study reports on characterization of low-infrared-emittance paint top-coatings for interior building applications in which the thermal radiation becomes important in comparison with thermal conductance. The top-coating that consist of a binder with aluminium flakes has been optically characterized in the infrared wavelength range in order to determine single flake and binder emittance from reflectance measurements. The single flake emittance was found to be 0.12 for non-leafing cornflake. The absorption coefficient that determines the binder emittance as a function of binder thickness was 0.060 [μm]−2 and 0.085 [μm]−2 for Lumiflon and polyester respectively. These results were used as parameters in a simple model of the flake-binder top-coating to investigate how the emittance of the top-coating was influence by the two components and compared with a state-of-art low-emittance commercial paint. It was found from the modelling that replacing the polyester binder with Lumiflon reduces the infrared emittance (at room temperature) from 0.36 to 0.30. Increasing flake reflectance from 0.88 to 0.96 and at the same time reduce flake thickness from 2 to 1μm gives an emittance of 0.20. However, the real samples prepared with Lumiflon showed a severe degradation caused by the flakes floating up closer to the surface which indicates a viscosity problem that needs to be solved for practical use. Thinner flakes with higher reflectance can be found if vacuum metallised pigments are used instead of ball-milled.

Effect of scandium on the optical properties of crystalline silicon material.

We have studied the optical properties of Sc-hyperdoped crystalline silicon based on quantum calculations. We have designed several probable configurations and found that the interstitial atomic positions of Sc (ScI, ScSI, ScTI, ScHI) are stable in the silicon matrix and can largely extend the absorption range of silicon from visible to infrared. The sub-band gap light absorption is attributed to the change of band structures of silicon and its intensity depends on the atomic concentration of Sc in silicon. The special effect of Sc on the properties of silicon will extend the sensitivity of silicon-based photodetectors to near infrared wavelength range.