Near-infrared Wavelength Range Research Articles

Ultrafast Coherent Absorption in Diamond Metamaterials.

Diamond is introduced as a material platform for visible/near-infrared photonic metamaterials, with a nanostructured polycrystalline diamond metasurface only 170 nm thick providing an experimental demonstration of coherent light-by-light modulation at few-optical-cycle (6 fs) pulse durations. "Coherent control" of absorption in planar (subwavelength-thickness) materials has emerged recently as a mechanism for high-contrast all-optical gating, with a speed of response that is limited only by the spectral width of the absorption line. It is shown here that a free-standing diamond membrane structured by focused ion beam milling can provide strong, spectrally near-flat absorption over a visible to near-infrared wavelength range that is wide enough (wider than is characteristically achievable in plasmonic metal metasurfaces) to facilitate coherent modulation of ultrashort optical pulses comprising only a few oscillations of electromagnetic field.

Hollow tubular potassium magnesium titanate with high thermal stability

Hollow tubular potassium magnesium titanate (KMTO) were synthesized using Mg(OH)2, TiO(OH)2 and K2CO3 as the raw materials and KCl as the flux. We studied the thermal stability of the KMTO and the reflectivity in the near-infrared wavelength range of KMTO treated at different temperatures. The results indicated that hollow tubular KMTO powders 4–15 μm in length and 1–2 μm in diameter could be obtained after being calclined at 850 °C for 2 h. The resulting KMTO powders had good thermal stability in structure and near-infrared reflectivity. Only a small amount of KMTO decomposed into MgTi2O5 and TiO2 when the as-calcined powders were post heat-treated at 1500 °C. Moreover, the high temperature treatment had only a minor effect on the high near-infrared reflectivities of KMTO. The results indicated that the prepared KMTO exhibited excellent thermal stability.

Extending absorption of near-infrared wavelength range for high efficiency CIGS solar cell via adjusting energy band

The efficient photon harvesting in near infrared wavelength range is still a challenging problem for high performance Cu(In1-x, Gax)Se2 (CIGS) solar cell. Herein, adjusting the energy band distribution of CIGS solar cell could provide significant academic guidance for devices with superior output electric power. To understand the role of each functional layer, the optimal 3000 nm CIGS absorber layer with 1.3 eV bandgap and 30 nm CdS buffer layer were firstly obtained via simulating the uniform band-gap structures. By introducing CIGS absorber layer with a double grading Ga/(Ga+In) profile, the power conversion efficiency of the double gradient band gap cell is superior to that of uniform band-gap cell through extending absorption of near-infrared wavelength range. Upon optimization, the best power conversion efficiency of CIGS with a double gradient band gap solar cell is improved significantly to 24.90%, among the best values reported in literatures, which is an 8.17% relative increase compared with that of the uniform band-gap cell. Our findings provide a theoretical guide toward the design of high performance solar cells and enrich the understandings of the energy band engineering for developing of novel semiconductor devices.

Growth mechanism of one-step self-masking reactive-ion-etching (RIE) broadband antireflective and superhydrophilic structures induced by metal nanodots on fused silica.

This work presents a low-cost, simple, convenient, advanced technology to prepare large-area defect-free subwavelength structures (SWSs). SWSs were obtained by a metal-induced one-step self-masking RIE process on a fused-silica surface, in which metal-fluoride (mainly ferrous-fluoride) nanodots were used to induce and gather stable fluorocarbon polymer etching inhibitors in the RIE polymers as masks. The SWS growth processes are visible with an increase in etching time and some exhibit prominent broadband antireflective properties from the visible to the near-infrared wavelength range. Transmission in the 600-900-nm range increased from approximately 93% for the polished fused silica to above 99% for the double-side SWSs on fused silica. A theoretical simulation by a finite-difference time-domain method agreed well with the experiments. Moreover, the surface of the SWSs exhibits excellent superhydrophilic properties.

Wide-angle broadband near-perfect all-dielectric metamaterial reflector

Compact nonabsorbing reflectors are useful in numerous important applications, such as surface protection against high-power irradiation, low-loss mirrors in laser cavities, and improvement of signal-to-noise ratios in bioimaging and nanosensing. We exploit the Mie resonance in periodically arranged silicon nanospheres to design a wide-angle broadband near-perfect all-dielectric metamaterial reflector. First, we obtain the reflectance of a semi-infinite dilute medium of dielectric spheres arranged in a simple-cubic lattice in air and deduce criteria such as the radius and period required to obtain a near-perfect mirror. Next, we construct a near-perfect broadband mirror using the metasurfaces in the near-infrared wavelength range for the period-to-radius ratio of ∼2.54 for normal incidence. Finally, we study the reflection characteristics of the multilayer nanosphere metamaterials. A near-perfect mirror is designed, which is independent of polarization, and the permitted incident-angle width reaches 40 deg for three layers of metamaterial. This is the first study to address the optimal structure parameters for metasurfaces and the reflection characteristics of multilayer metamaterials. Our findings provide guidelines for the design of photonic devices based on dielectric metamaterials.

Supercontinuum generation in photonic crystal fibres with core filled with toluene

A photonic crystal fibre with hollow core filled with toluene is considered as a new system for coherent supercontinuum generation. The dispersion characteristics are studied for various geometrical parameters of photonic crystal fibres. Two structures with lattice constant 2 μm, filling factors d/Λ 0.3 and 0.35 and toluene core of diameters of 3.34 and 3.23 μm have flat dispersion in the near infrared range. The structure with d/Λ = 0.3 has all-normal dispersion characteristics in whole near-infrared wavelength range, while the second structure (d/Λ = 0.35) has anomalous dispersion for wavelengths longer than 1.5 μm. Although confinement losses in the considered structures are as high as 0.4 dB cm−1, we show that the generation of coherent supercontinuum in the range 1.0–1.7 μm with the pulse energy conversion of 16% is feasible in 4 cm long fibre samples with standard fibre femtosecond lasers.

Temporal and spatial variations of the absolute reflectivity of Jupiter and Saturn from 0.38 to 1.7μm with PlanetCam-UPV/EHU

We provide measurements of the absolute reflectivity of Jupiter and Saturn along their central meridians in filters covering a wide range of visible and near-infrared wavelengths (from 0.38 to 1.7 $\mu$m) that are not often presented in the literature. We also give measurements of the geometric albedo of both planets and discuss the limb-darkening behavior and temporal variability of their reflectivity values for a period of four years (2012-2016). This work is based on observations with the PlanetCam-UPV/EHU instrument at the 1.23 m and 2.2 m telescopes in Calar Alto Observatory (Spain). The instrument simultaneously observes in two channels: visible (VIS; 0.38-1.0 $\mu$m) and short-wave infrared (SWIR; 1.0--1.7 $\mu$m). We obtained high-resolution observations via the lucky-imaging method. We show that our calibration is consistent with previous independent determinations of reflectivity values of these planets and, for future reference, provide new data extended in the wavelength range and in the time. Our results have an uncertainty in absolute calibration of 10--20\%. We show that under the hypothesis of constant geometric albedo, we are able to detect absolute reflectivity changes related to planetary temporal evolution of about 5-10\%.

Direct Amplitude-Phase Near-Field Observation of Higher-Order Anapole States.

Anapole states associated with the resonant suppression of electric-dipole scattering exhibit minimized extinction and maximized storage of electromagnetic energy inside a particle. Using numerical simulations, optical extinction spectroscopy, and amplitude-phase near-field mapping of silicon dielectric disks, we demonstrate high-order anapole states in the near-infrared wavelength range (900-1700 nm). We develop the procedure for unambiguously identifying anapole states by monitoring the normal component of the electric near-field and experimentally detect the first two anapole states as verified by far-field extinction spectroscopy and confirmed with the numerical simulations. We demonstrate that higher-order anapole states possess stronger energy concentration and narrower resonances, a remarkable feature that is advantageous for their applications in metasurfaces and nanophotonics components, such as nonlinear higher-harmonic generators and nanoscale lasers.

Optical properties of mice's stool in 550 to 1000 nm wavelength range.

The aim of this work was to measure optical properties of stool of mice to provide this relevant wavelength-dependent behavior for optical imaging modalities such as fluorescent molecular tomography and near-infrared optical tomography. BALB/c nude female mice were studied and optical properties of the stool were determined by employing the inverse adding-doubling approach. The animals were kept on chlorophyll-free diet. Nine stool samples were measured. The wavelength-dependent behavior of absorption and scattering in 550 to 1000 nm range is presented. The reduced scattering spectrum is fitted to the Mie scattering approximation in the near-infrared (NIR) wavelength range and to the Mie + Rayleigh approximation in visible/NIR range with the fitting coefficients presented. The study revealed that the absorption spectrum of stool can lead to crosstalk with the spectrum of hemoglobin in the NIR range.

Optical sensing with Anderson-localised light

We show that fabrication imperfections in silicon nitride photonic crystal waveguides can be used as a resource to efficiently confine light in the Anderson-localised regime and add functionalities to photonic devices. Our results prove that disorder-induced localisation of light can be utilised to realise an alternative class of high-quality optical sensors operating at room temperature. We measure wavelength shifts of optical resonances as large as 15.2 nm, more than 100 times the spectral linewidth of 0.15 nm, for a refractive index change of about 0.38. By studying the temperature dependence of the optical properties of the system, we report wavelength shifts of up to about 2 nm and increases of more than a factor 2 in the quality factor of the cavity resonances, when going from room to cryogenic temperatures. Such a device can allow simultaneous sensing of both local contaminants and temperature variations, monitored by tens of optical resonances spontaneously appearing along a single photonic crystal waveguide. Our findings demonstrate the potential of Anderson-localised light in photonic crystals for scalable and efficient optical sensors operating in the visible and near-infrared range of wavelengths.

Broadband polarization conversion with anisotropic plasmonic metasurfaces

Metasurfaces offer exciting opportunities that enable precise control of light propagation, optical intensity, phase and polarization. Plasmonic metasurface based quarter-wave plates have been recently studied to realize the conversion between linear polarization and circular polarization. However, it is still quite challenging to directly measure the birefringent phase retardation introduced by metasurface wave plates with a reliable technique. Here, we report a high-performance broadband metasurface quarter-wave plate made of anisotropic T-shaped plasmonic antennas in near-infrared wavelength range, where the achromatic nearly 90° transmitted phase retardation through the metasurface is precisely characterized with an optical vortex based interferometric approach. Based on the measured transmission amplitude and phase of two orthogonal linear polarization components, nearly unit degree of linear polarization is extracted from the Stokes parameters, indicating excellent broadband polarization conversion between linearly and circularly polarized light through the metasurface. Our results will be an important step forward in the advancement of integrated metasurface devices for polarization conversion and beam manipulation, structured light control, as well as new spectroscopic and interferometric techniques for metasurface characterization.

Reflectance modulation using SiO2/TiO2 multilayer structures prepared by sol-gel spin coating process for optical applications

Passive devices made of SiO2/TiO2 bilayers have been demanded for the molding of electromagnetic waves in optical waveguides, microcavities, solar cells, sensors and so on. Here, we present the fabrication and characterization of SiO2/TiO2 multilayer structures as reflectors. The refractive indices were found to be 1.43 & 2.0 with thicknesses 230 & 70 nm corresponding to the SiO2 and TiO2 films respectively. AFM surface topography study showed little bit large surface roughness of the TiO2 as compared to SiO2 film due to its large grain size. The corresponding reflectance enhancement was noticed with the increased number of bilayers of SiO2/TiO2 films. Furthermore, six alternate layers of SiO2/TiO2 demonstrated the as much as 78% reflectance in the near-infrared wavelength range.

Solid-State Plasmonic Solar Cells.

Metallic nanoparticles such as silver and gold show localized surface plasmon resonances (LSPRs), which are associated with near-field enhancement effects in the vicinity of nanoparticles. Therefore, strong light-matter interaction is induced by the near-field enhancement effects of LSPRs. Because the resonant wavelength of LSPRs can be easily controlled by the size and shape of the metallic nanoparticles in the visible and near-infrared wavelength range, LSPRs have received considerable attention as optical antennae for light energy conversion systems such as solar cells. LSPRs decay very quickly as a result of light scattering and excitation of electron-hole pairs in the metal itself. However, in addition to the near-field enhancement effect, this light scattering and electron-hole pair excitation, which are known to cause loss of LSPRs, can be utilized as a solar cell enhancement mechanism. Here, we focus on plasmonic solid-state solar cells. The mechanisms of the light scattering by LSPRs, near-field enhancement, and plasmon-induced charge separation based on electron-hole pair excitations can be clarified. We review the related studies from the viewpoint of these mechanisms rather than material science.

Single-Layer Plasmonic Metasurface Half-Wave Plates with Wavelength-Independent Polarization Conversion Angle

Manipulation of polarization state is of great fundamental importance and plays a crucial role in modern photonic applications such as optical communication, imaging, and sensing. Metamaterials and metasurfaces have attracted increasing interest in this area because they facilitate designer optical response through engineering the composite subwavelength structures. Here we propose a general methods of designing half-wave plate and demonstrate in the near-infrared wavelength range an optically thin plasmonic metasurface half-wave plates that rotate the polarization direction of the linearly polarized incident light with a high degree of linear polarization. The half-wave plate functionality is realized through arranging the orientation of the nanoantennas to form an appropriate spatial distribution profile, which behave exactly as in classical half-wave plates but over in a wavelength-independent way.

Free-standing plasmonic metal-dielectric-metal bandpass filter with high transmission efficiency

Plasmonic spectrum filtering devices based on metallic nanostructures have attracted wide attention due to their good reliability, ease of fabrication, and wideband tunability. However, the presence of thick substrate significantly limits the structure’s longitudinal size for further optoelectronic integration and reduces the devices’ performance. Here we propose and demonstrate an ultra-thin plasmonic bandpass filter based on free-standing periodic metal-dielectric-metal stack geometry working in the near-infrared wavelength range. The coupling between free-space electromagnetic waves and spatially confined plasmonic modes in the designed structure is systematically investigated. As demonstrated in the calculation and experiment, the free-standing plasmonic filters have more than 90% transmission efficiency and superior angular tolerance. The experimental results are in good agreement with the theoretical calculations. These artificial nanostructured filtering devices may find potential applications in the extremely compact device architectures.

Biocompatible Chitosan-Carbon Dot Hybrid Nanogels for NIR-Imaging-Guided Synergistic Photothermal-Chemo Therapy.

Multifunctional nanocarriers with good biocompatibility, good imaging function, and smart drug delivery ability are crucial for realizing highly efficient imaging-guided chemotherapy in vivo. This paper reports a type of chitosan-carbon dot (CD) hybrid nanogels (CCHNs, ∼65 nm) by integrating pH-sensitive chitosan and fluorescent CDs into a single nanostructure for simultaneous near-infrared (NIR) imaging and NIR/pH dual-responsive drug release to improve therapeutic efficacy. Such CCHNs were synthesized via a nonsolvent-induced colloidal nanoparticle formation of chitosan-CD complexes assisted by ethylenediaminetetraacetic acid (EDTA) molecules in the aqueous phase. The selective cross-linking of chitosan chains in the nanoparticles can immobilize small CDs complexed in the chitosan networks. The resultant CCHNs display high colloidal stability, high loading capacity for doxorubicin (DOX), bright and stable fluorescence from UV to NIR wavelength range, efficient NIR photothermal conversion, and intelligent drug release in response to both NIR light and change in pH. The results from in vitro tests on cell model and in vivo tests on different tissues of animal model indicate that the CCHNs are nontoxic. The DOX-loaded CCHNs can permeate into the implanted tumor on mice and release drug molecules efficiently on site to inhibit tumor growth. The additional photothermal treatments from NIR irradiation can further inhibit the tumor growth, benefited from the effective NIR photothermal conversion of CCHNs. The demonstrated CCHNs manifest a great promise toward multifunctional intelligent nanoplatform for highly efficient imaging-guided cancer therapy with low side effects.

The PMA Catalogue: 420 million positions and absolute proper motions

Abstract We present a catalogue that contains about 420 million absolute proper motions of stars. It was derived from the combination of positions from Gaia DR1 and 2MASS, with a mean difference of epochs of about 15 yr. Most of the systematic zonal errors inherent in the 2MASS Catalogue were eliminated before deriving the absolute proper motions. The absolute calibration procedure (zero-pointing of the proper motions) was carried out using about 1.6 million positions of extragalactic sources. The mean formal error of the absolute calibration is less than 0.35 mas yr−1. The derived proper motions cover the whole celestial sphere without gaps for a range of stellar magnitudes from 8 to 21 mag. In the sky areas where the extragalactic sources are invisible (the avoidance zone), a dedicated procedure was used that transforms the relative proper motions into absolute ones. The rms error of proper motions depends on stellar magnitude and ranges from 2–5 mas yr−1 for stars with 10 mag < G < 17 mag to 5–10 mas yr−1 for faint ones. The present catalogue contains the Gaia DR1 positions of stars for the J2015 epoch. The system of the PMA proper motions does not depend on the systematic errors of the 2MASS positions, and in the range from 14 to 21 mag represents an independent realization of a quasi-inertial reference frame in the optical and near-infrared wavelength range. The Catalogue also contains stellar magnitudes taken from the Gaia DR1 and 2MASS catalogues. A comparison of the PMA proper motions of stars with similar data from certain recent catalogues has been undertaken.

Analysis of the Intrinsic Mid-infrared L band to Visible–Near-infrared Flux Ratios in Spectral Synthesis Models of Composite Stellar Populations

Abstract We analyze the intrinsic flux ratios of various visible–near-infrared filters with respect to 3.5 μm for simple and composite stellar populations (CSPs), and their dependence on age, metallicity, and star formation history (SFH). UV/optical light from stars is reddened and attenuated by dust, where different sightlines across a galaxy suffer varying amounts of extinction. Tamura et al. (2009) developed an approximate method to correct for dust extinction on a pixel-by-pixel basis, dubbed the “ ” method, by comparing the observed flux ratio to an empirical estimate of the intrinsic ratio of visible and ∼3.5 μm data. Through extensive modeling, we aim to validate the “ ” method for various filters spanning the visible through near-infrared wavelength range, for a wide variety of simple and CSPs. Combining Starburst99 and BC03 models, we built spectral energy distributions (SEDs) of simple (SSP) and composite (CSP) stellar populations for various realistic SFHs, while taking metallicity evolution into account. We convolve various 0.44–1.65 μm filter throughput curves with each model SED to obtain intrinsic flux ratios . When unconstrained in redshift, the total allowed range of is 0.6–4.7, or almost a factor of eight. At known redshifts, and in particular at low redshifts (z ≲ 0.01), is predicted to span a narrow range of 0.6–1.9, especially for early-type galaxies (0.6–0.7), and is consistent with observed values. The method can therefore serve as a first-order dust-correction method for large galaxy surveys that combine JWST (rest-frame 3.5 μm) and HST (rest-frame visible–near-IR) data.

(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 propagation in ultra-thin gap in 3D photonic crystals

We investigate the propagation of light in an ultra-thin gap in stacked-stripe three-dimensional (3D) photonic crystals operating in the near-infrared wavelength range. We fabricate 3D photonic crystals composed of 32 stacked layers with an artificially introduced gap (∼200nm) in the center of the structure by using a wafer bonding method. In order to study the characteristics of the gap, we introduce oblique waveguides to connect the gap with the upper and lower sides of the photonic crystal. The observation of light output from waveguides that are distant from the waveguide used for incident light demonstrates for the first time that light propagates along the air gap and is distributed to multiple output waveguides. Moreover, we perform calculations that reveal the formation of a propagation mode resulting from introduction of the ultra-thin gap. We analyze the coupling between the propagation mode and the oblique waveguide mode and discuss the characteristics of light distribution via the gap.