Wide Range Of Visible Wavelengths Research Articles

Broadband single-cell-driven multifunctional metalensing

Metasurfaces are artificially engineered ultrathin photonic components that can be freely designed to exhibit unprecedented capabilities of highly-efficient electromagnetic wave manipulation. The ever-growing demand for miniaturized photonic devices for emerging applications, like imaging, spectroscopy, biosensing, and quantum information processing, consistently requires broadband multifunctional and highly-efficient meta-devices. Recent years have witnessed tremendous advancements in metasurfaces; however, investigating the novel platform to realize broadband metasurfaces that integrate multiple functionalities in a single-layered structure would be an obvious technological extension. Here, we present a broadband single-cell-driven multifunctional metasurface platform capable of manipulating electromagnetic waves over a wide range of visible wavelengths (475−650 nm). A lossless zinc sulfide material exhibiting a sufficiently large refractive index and negligible extension coefficient across the visible spectrum is exploited to demonstrate the state-of-the-art meta-devices. Furthermore, a well-known spin-decoupling technique is implemented to multiplex different optical phenomena into a single-cell-driven structure. For proof of the concept, we demonstrate two meta-devices that provide transverse and longitudinal splitting of different optical phenomena for the visible wavelengths. The presented zinc sulfide material and unique design philosophy to achieve broadband multifunctional meta-devices may find potential applications in polarization and dispersion analyzers, sensing, optical communication, and many more.

Refractive Index of Supercooled Water Down to 230.3 K in the Wavelength Range between 534 and 675 nm

Knowledge of the refractive index of water in the deeply supercooled metastable liquid state is important, for example, for an accurate description of optical reflection and refraction processes occurring in clouds. However, a measurement of both the temperature and wavelength dependence of the refractive index under such extreme conditions is challenging. Here, we employ Raman spectroscopy in combination with microscopic water jets in vacuum to obtain the refractive index of supercooled water to a lowest temperature of 230.3 K. While our approach is based on the analysis of Mie resonances in Raman spectra measured by using a single excitation wavelength at 532 nm, it allows us to obtain the refractive index in a wide visible wavelength range from 534 to 675 nm. Because of a direct link between the refractive index and density of water, our results provide a promising approach to help improve our understanding of water's anomalous behavior.

A potential EARLY FLOWERING 3 homolog in Chlamydomonas is involved in the red/violet and blue light signaling pathways for the degradation of RHYTHM OF CHLOROPLAST 15.

Light plays a major role in resetting the circadian clock, allowing the organism to synchronize with the environmental day and night cycle. In Chlamydomonas the light-induced degradation of the circadian clock protein, RHYTHM OF CHLOROPLAST 15 (ROC15), is considered one of the key events in resetting the circadian clock. Red/violet and blue light signals have been shown to reach the clock via different molecular pathways; however, many of the participating components of these pathways are yet to be elucidated. Here, we used a forward genetics approach using a reporter strain that expresses a ROC15-luciferase fusion protein. We isolated a mutant that showed impaired ROC15 degradation in response to a wide range of visible wavelengths and impaired light-induced phosphorylation of ROC15. These results suggest that the effects of different wavelengths converge before acting on ROC15 or at ROC15 phosphorylation. Furthermore, the mutant showed a weakened phase resetting in response to light, but its circadian rhythmicity remained largely unaffected under constant light and constant dark conditions. Surprisingly, the gene disrupted in this mutant was found to encode a protein that possessed a very weak similarity to the Arabidopsis thaliana EARLY FLOWERING 3 (ELF3). Our results suggest that this protein is involved in the many different light signaling pathways to the Chlamydomonas circadian clock. However, it may not influence the transcriptional oscillator of Chlamydomonas to a great extent. This study provides an opportunity to further understand the mechanisms underlying light-induced clock resetting and explore the evolution of the circadian clock architecture in Viridiplantae.

Straight-chain alkanediol derivatives leading to glassy cholesteric liquid crystals with visible reflection

ABSTRACT Straight-chain alkanediols such as ethylene glycol are commonly found in our daily life as they are used to produce cosmetics, antifreezes, polyesters and polyurethanes. In this article, we report on the promising potential use of straight-chain alkanediols for rewritable full-colour imaging applications by the preparation of glassy cholesteric liquid crystals (G-CLCs). A series of straight-chain alkanediol derivatives possessing two cholesteryl groups through carbonate ester linkages (Cn-DiCh) showed thermotropic cholesteric liquid crystal phase with visible reflection. The thermally induced shifting ranges of reflection peaks were dependent on the central carbon chain length (n) of Cn-DiCh. Although the pristine Cn-DiCh showed narrow wavelength ranges of the reflection peaks by changing the temperature, we successfully prepared a mixture of two different kinds of Cn-DiCh at their equivalent weight ratio, which exhibited the reflection peak shift throughout a wide visible-wavelength range between 400 nm and 850 nm. Moreover, the binary mixtures of Cn-DiCh were rapidly cooled from the CLC temperatures to 0°C, whereupon the reflection colours could be preserved even at room temperature over 2 months. Such rapid cooling treatment enabled the straightforward preparation of solid-state G-CLCs with visible reflection characteristics, thereby leading to the applications of rewritable full-colour imaging media.

Multi-component supramolecular gels induce protonation of a porphyrin exciplex to achieve improved collective optical properties for effective photocatalytic hydrogen generation.

Towards mimicking natural photosystems, supramolecular gels containing two types of porphyrins were developed for photocatalysis. Protonation and J-aggregation of porphyrins within gels expand the absorption to a wide range of visible wavelengths. Porphyrin exciplex formation renders a smaller bandgap for photo-induced electron generation. These features induce effective photocatalytic hydrogen generation.

Structure-Function Correlations in Sputter Deposited Gold/Fluorocarbon Multilayers for Tuning Optical Response.

A new strategy to nanoengineer gold/fluorocarbon multilayer (ML) nanostructures is reported. We have investigated the morphological changes occurring at the metal–polymer interface in ML structures with varying volume fraction of gold (Au) and the kinetic growth aspect of the microscale properties of nano-sized Au in plasma polymer fluorocarbon (PPFC). Investigations were carried out at various temperatures and annealing times by means of grazing incidence small-angle and wide-angle X-ray scattering (GISAXS and GIWAXS). We have fabricated a series of MLs with varying volume fraction (0.12, 0.27, 0.38) of Au and bilayer periodicity in ML structure. They show an interesting granular structure consisting of nearly spherical nanoparticles within the polymer layer. The nanoparticle (NP) morphology changes due to the collective effects of NPs diffusion within ensembles in the in-plane vicinity and interlayer with increasing temperature. The in-plane NPs size distinctly increases with increasing temperature. The NPs become more spherical, thus reducing the surface energy. Linear growth of NPs with temperature and time shows diffusion-controlled growth of NPs in the ML structure. The structural stability of the multilayer is controlled by the volume ratio of the metal in polymer. At room temperature, UV-Vis shows a blue shift of the plasmon peak from 560 nm in ML Au/PTFE_1 to 437 nm in Au/PTFE_3. We have identified the fabrication and postdeposition annealing conditions to limit the local surface plasmon resonance (LSPR) shift from = 180 nm (Au/PTFE_1) to = 67 nm (Au/PTFE_3 ML)) and their optical response over a wide visible wavelength range. A variation in the dielectric constant of the polymer in presence of varying Au inclusion is found to be a possible factor affecting the LSPR frequency. Our findings may provide insights in nanoengineering of ML structure that can be useful to systematically control the growth of NPs in polymer matrix.

Femtosecond Direct Laser-Induced Assembly of Monolayer of Gold Nanostructures with Tunable Surface Plasmon Resonance and High Performance Localized Surface Plasmon Resonance and Surface Enhanced Raman Scattering Sensing.

We show femtosecond direct laser-induced assembly of gold nanostructures with plasmon resonance band variable as a function of laser irradiation in a wide range of visible wavelengths. A system of 2-photon lithography is used to achieve site-selectively controlled dewetting of a thin gold film into nanostructures in which size and shape are highly dependent on the laser power. Simultaneous measurements of localized surface plasmon resonance (LSPR) and surface enhanced Raman scattering (SERS) in the presence of various concentrations of trans-1,2-bis(4-pyridyl) ethylene (BPE) as target molecule are performed in order to highlight the relationship between structural dimensions, plasmonic effect, and detection activity. The resulting gold NPs exhibit high sensitivity as both LSPR and SERS sensors and allow the detection of picomolar concentrations of BPE with a SERS enhancement factor (SEF) of 1.33 × 109 and a linear detection range between 10-3 and 10-12 M.

Measurements of complex refractive index change of photoactive yellow protein over a wide wavelength range using hyperspectral quantitative phase imaging

A novel optical holographic technique is presented to simultaneously measure both the real and imaginary components of the complex refractive index (CRI) of a protein solution over a wide visible wavelength range. Quantitative phase imaging was employed to precisely measure the optical field transmitted from a protein solution, from which the CRIs of the protein solution were retrieved using the Fourier light scattering technique. Using this method, we characterized the CRIs of the two dominant structural states of a photoactive yellow protein solution over a broad wavelength range (461–582 nm). The significant CRI deviation between the two structural states was quantified and analysed. The results of both states show the similar overall shape of the expected rRI obtained from the Kramers–Kronig relations.

Star-shaped and linear π-conjugated oligomers consisting of a tetrathienoanthracene core and multiple diketopyrrolopyrrole arms for organic solar cells.

Solution-processable star-shaped and linear π-conjugated oligomers consisting of an electron-donating tetrathienoanthracene (TTA) core and electron-accepting diketopyrrolopyrrole (DPP) arms, namely, TTA-DPP4 and TTA-DPP2, were designed and synthesized. Based on density functional theory calculations, the star-shaped TTA-DPP4 has a larger oscillator strength than the linear TTA-DPP2, and consequently, better photoabsorption property over a wide range of visible wavelengths. The photovoltaic properties of organic solar cells based on TTA-DPP4 and TTA-DPP2 with a fullerene derivative were evaluated by varying the thickness of the bulk heterojunction active layer. As a result of the enhanced visible absorption properties of the star-shaped π-conjugated structure, better photovoltaic performances were obtained with relatively thin active layers (40–60 nm).

Growth kinetics and surface properties of single-crystalline aluminum-doped zinc oxide nanowires on silicon substrates

We present here the results from a systematic investigation on the growth kinetics and surface properties of Al-doped ZnO (AZO) nanowires synthesized on (001)Si substrates under different hydrothermal conditions. The as-synthesized vertical AZO nanowires exhibited a hydrophilic characteristic and their crystal structures were determined to be perfectly single crystalline with the axis of the wire parallel to the [0001] direction. TEM and EDS results revealed that the as-synthesized AZO nanowires have tapered tips, and the Al-doped concentration in the AZO nanowires was about 1.6at%. After a series of SEM examinations, the average length of AZO nanowires synthesized at each temperature studied was found to follow a linear relationship with the reaction time, indicating that the hydrothermal growth of AZO nanowires was a reaction-controlled process. The activation energy for linear growth of AZO nanowires on Si substrate, as obtained from an Arrhenius plot, was found to be about 46kJ/mol. From UV–vis spectroscopic measurements, it was found that the Si substrate coated with vertically-aligned AZO nanowire arrays exhibited remarkably reduced reflectance (10–12%) over a wide range of visible wavelengths (400–800nm) and angles of light incidence (8–60°). The good broadband and omnidirectional antireflection characteristics can be attributed to the light trapping effect and the graded refractive index resulting from the tapered AZO nanowire structures.

Metal-polymer nanocomposite with stable plasmonic tuning under cyclic strain conditions

We report the fabrication and characterization of stretchable nanocomposite films with mechanically tunable surface plasmon resonance. The films have been produced by implantation in a Polydimethylsiloxane substrate of neutral gold nanoparticles aerodynamically accelerated in a supersonic expansion. Optical absorption spectroscopy shows that uniaxial stretching of the nanocomposite induce a reversible redshift of the plasmon peak up to 180 nm from the peak wavelength of the non-stretched sample. The range of the plasmon peak shift depends upon the density of implanted nanoparticles. The optical behavior of the nanocomposite evolves upon cyclical stretching due to the rearrangement of the nanoparticles in the elastomeric matrix. We have identified the fabrication and post-deposition treatment conditions to stabilize the plasmonic shift upon cyclical stretching in order to obtain robust and large area nanocomposites with tunable and reproducible optical properties over a wide visible wavelength range.

Improved oxidative stability of sunflower oil in the presence of an oxygen‐scavenging film

AbstractThe oxidative stability of sunflower oil (SFO) was measured during storage at 23 and 37°C in the presence of a novel oxygen‐scavenging film that contained polyfuryloxirane (PFO). Commercially refined and deodorized SFO was stored in a lighted room in sealed transparent packages containing either PFO film or an antioxidant, 0.02% butylated hydroxytoluene (BHT). Oxidative stability was evaluated by determination of peroxide values and gas‐chromatographic measurement of headspace hexanal. SFO stored in the presence of the oxygen‐scavenging film was more stable than oil stored without the film, or than film stored with 0.02% BHT. The PFO film scavenges oxygen through energy‐transfer sensitization of singlet oxygen. The film is doped with eosin and the naturally‐occurring dye, curcumin, which absorb over a wide range of visible wavelengths. Curcumin transfers its absorbed energy to eosin, which sensitizes the production of singlet oxygen. The singlet oxygen is scavenged by PFO. The use of two dyes increases the efficiency of the sensitization process, reducing the illumination time and intensity required for effective oxygen scavenging.