Short-wavelength Illumination Research Articles

Uniform Huygens Metasurfaces with Postfabrication Phase Pattern Recording Functionality

With the rapid progress in the field of metasurfaces and their use in miniature integrated devices arises the quest for cheap mass production of efficient metasurfaces. We suggest a novel way to design and fabricate phase-gradient Huygens metasurfaces using laser-annealing of uniform particles made of As2S3 chalcogenide glass. We show that a phase gradient metasurface can be realized by tuning the refractive index of otherwise identical meta-atoms instead of tuning their geometry. We are using an array of identical As2S3 particles with the possibility to locally change their refractive index using a short-wavelength illumination (green laser) in order to tune the phase pattern at the postfabrication stage. Metasurfaces fabricated with this method can be used for operation in the red or IR spectral range. We fabricate uniform As2S3 Huygens metasurfaces using electron beam lithography and demonstrate their postfabrication tuning with exposure of comparatively low intensity. Sample characterizations with transmittance measurements and quantitative phase microscopy provide results in good correspondence with numerical predictions confirming postfabrication spectral tuning. Using such tuning, we demonstrate the possibility of transferring the intensity pattern produced by modifying a writing beam with a spatial light modulator to a phase pattern recorded on a uniform As2S3 metasurface. Our method has potential advantages for the low-cost production of large-scale metasurfaces because uniform geometries are better adjusted for mass manufacturing.

(n+/p/p+) Silicon solar cell base thickness optimization under modulated short wavelength illumination, at resonances in both frequency and temperature of minority carriers’ diffusion coefficient

The magneto-transport equation relating to the density of photogenerated minority carriers in the (p) base of the (n+/p/p+) solar cell illuminated by monochromatic light in frequency modulation, is solved. The diffusion coefficient of the minority carriers in the base, placed under temperature and magnetic field variation, passes through a maximum, at the double resonance points, in temperature and at the frequency of the cyclotron. The photocurrent is reproduced as a function of the recombination velocity at the junction, for the maximum values of the diffusion coefficient. The expressions of the minority carriers ’recombination velocity on the rear side are deduced and their graphical representation gives the optimum thickness, specific to a high absorption coefficient, for the maximum values of the diffusion coefficient. The results obtained from the optimum thickness are modelled and analyzed, in favor of a reduction of silicon material, for the development of economical solar cells.

Light-Induced Degradation of Metal-Free Organic Perovskites.

Perovskites have attracted great interest in optoelectronics and photonics. As a new class of perovskites, metal-free perovskites have drawn growing attention due to the absence of toxic metal elements in them and their wide chemical diversity. Taking MDABCO-NH4I3 (MDBACO = N-methyl-N'-diazabicyclo[2.2.2]octonium) and MDABCO-NH4Br3 as examples, our first-principles calculations discover two fundamental features of metal-free perovskites that should be crucial for their applications. First, their photoluminescence emission originates from halogen vacancies, instead of the self-trapped exciton generally suggested. Second, in the vicinity of a halogen vacancy, optical excitation from the valence bands to the empty defect bands may cause release of H2 and NH3 molecules, which will not only lead to degradation of the perovskite but also quench its photoluminescence. To prevent the degradation and protect the optoelectronic and photonic performances of metal-free perovskites, short-wavelength illumination needs to be shielded.

Plasmoelectric Potential in Plasmon-Mediated Electrochemistry.

Plasmon-mediated chemical reactions have attracted intensive research interest as a means of achieving desirable reaction yields and selectivity. The energetic charge carriers and elevated local temperature induced by the nonradiative decay of surface plasmons are thought to be responsible for improving reaction outcomes. This study reports that the plasmoelectric potential is another key contributor in plasmon-mediated electrochemistry. Additionally, we disclose a convenient and reliable method for quantifying the specific contributions of the plasmoelectric potential, hot electrons, and photothermal heating to the electroreduction of oxygen at the plasmonic Ag electrode, revealing that the plasmoelectric potential is the dominating nonthermal factor under short-wavelength illumination and moderate electrode bias. This work elucidates novel mechanistic understandings of plasmon-mediated electrochemistry, facilitating high-performance plasmonic electrocatalyst design optimization.

Light Pollution and Circadian Misalignment: A Healthy, Blue-Free, White Light-Emitting Diode to Avoid Chronodisruption.

Sunlight has participated in the development of all life forms on Earth. The micro-world and the daily rhythms of plants and animals are strongly regulated by the light–dark rhythm. Human beings have followed this pattern for thousands of years. The discovery and development of artificial light sources eliminated the workings of this physiological clock. The world’s current external environment is full of light pollution. In many electrical light bulbs used today and considered “environmentally friendly,” such as LED devices, electrical energy is converted into short-wavelength illumination that we have not experienced in the past. Such illumination effectively becomes “biological light pollution” and disrupts our pineal melatonin production. The suppression of melatonin at night alters our circadian rhythms (biological rhythms with a periodicity of 24 h). This alteration is known as chronodisruption and is associated with numerous diseases. In this article, we present a blue-free WLED (white light-emitting diode) that can avoid chronodisruption and preserve circadian rhythms. This WLED also maintains the spectral quality of light measured through parameters such as CRI (color reproduction index).

Wavelength-dependent electrical response of an organic circuit for color sensing without external filters

The use of organic semiconductors in photodetectors has led to promising results in low-cost light sensing. Although the relatively narrow absorption band of most organic compounds limits their use as wide-band photodetectors, the selection of materials with the desired spectral properties permits the fabrication of wavelength-selective sensors without external color filters. Here, we present a polymer-gated organic complementary inverter circuit exhibiting wavelength-dependent output voltage change that enables dual color sensing via the use of organic semiconductors (PTCDI-C5 and pentacene) with distinct absorption spectra. When illuminated, the inverter circuit shows a wavelength (color)-dependent output voltage change due to the difference in the spectral properties of the semiconductors. Compared to the dark state, the output voltage of the circuit increases under long-wavelength and decreases under short-wavelength illumination. These findings demonstrate a novel use of photoresponsive organic semiconductors to construct simple dual-color sensitive sensors which may simplify the fabrication of multi-wavelength detector circuits.

Down-Regulation of the Ultraviolet-Sensitive Visual Pigment of the Cockroach Decreases the Masking Effect in Short-Wavelength Illumination

Down-Regulation of the Ultraviolet-Sensitive Visual Pigment of the Cockroach Decreases the Masking Effect in Short-Wavelength Illumination

Super-resolution imaging on multilayer sample by microsphere-assisted microscope

Microsphere-assisted super-resolution imaging (MSI) is a label-free and wide-field imaging technique, which draws much attention in the field. Here, a novel characteristic of MSI was reported. We demonstrated microsphere-assisted microscope possesses certain tomographic ability in the imaging of multilayer structure sample, Blu-ray disc (BD), resolving both periodic stripes and sub-surface recording marks which locate at different lays on BD, and performs the best vertical resolving under a short-wavelength illumination. Moreover, the magnification generated by microsphere and the lateral resolution in MSI, as well as their relationship, were discussed. Furthermore, our experiments show that a higher relative refractive index between the microsphere and immersion medium brings greater magnification, rather than better resolution, and theoretical simulation suggests that narrower beam waist focused by microsphere leads to better resolution in MSI.

Monitoring Dark-State Dynamics of a Single Nitrogen-Vacancy Center in Nanodiamond by Auto-Correlation Spectroscopy: Photonionization and Recharging.

In this letter, the photon-induced charge conversion dynamics of a single Nitrogen-Vacancy (NV) center in nanodiamond between two charge states, negative (NV−) and neutral (NV0), is studied by the auto-correlation function. It is observed that the ionization of NV− converts to NV0, which is regarded as the dark state of the NV−, leading to fluorescence intermittency in single NV centers. A new method, based on the auto-correlation calculation of the time-course fluorescence intensity from NV centers, was developed to quantify the transition kinetics and yielded the calculation of transition rates from NV− to NV0 (ionization) and from NV0 to NV− (recharging). Based on our experimental investigation, we found that the NV−-NV0 transition is wavelength-dependent, and more frequent transitions were observed when short-wavelength illumination was used. From the analysis of the auto-correlation curve, it is found that the transition time of NV− to NV0 (ionization) is around 0.1 μs, but the transition time of NV0 to NV− (recharging) is around 20 ms. Power-dependent measurements reveal that the ionization rate increases linearly with the laser power, while the recharging rate has a quadratic increase with the laser power. This difference suggests that the ionization in the NV center is a one-photon process, while the recharging of NV0 to NV− is a two-photon process. This work, which offers theoretical and experimental explanations of the emission property of a single NV center, is expected to help the utilization of the NV center for quantum information science, quantum communication, and quantum bioimaging.

Microsphere assisted optical super-resolution imaging with narrowband illumination

Microsphere assisted microscopy is a facile and affordable super-resolution technique. Here, we explored fully liquid-immersed high-index (n=1.9, 2.1) microsphere assisted super-resolution imaging with narrowband light illumination. The influence of illumination wavelengths and the relative refractive index between microspheres and immersion media on imaging are experimentally investigated, as well as the relationship between the magnification generated by microspheres and imaging position. Blu-ray disk with 120 nm/180 nm stripe structure can be resolved with low-numerical-aperture (NA) microscope objective (10×, NA=0.35) with appropriate imaging parameters, which achieves super-resolution observation in a low-cost and convenient way. The combination with high relative refractive index between microsphere (n=2.1) and immersion medium (n=1.33) shows the best resolution and magnification (∼8). In addition, the dark spot generally appearing in the center of the microsphere in super-resolution imaging is studied. Thus we propose the approach to obtain optimal super-resolution imaging effect by combining narrowband short-wavelength illumination and high relative refractive index between microspheres and immersion media.

Optical Control of Cardiac Function with a Photoswitchable Muscarinic Agonist.

Light-triggered reversible modulation of physiological functions offers the promise of enabling on-demand spatiotemporally controlled therapeutic interventions. Optogenetics has been successfully implemented in the heart, but significant barriers to its use in the clinic remain, such as the need for genetic transfection. Herein, we present a method to modulate cardiac function with light through a photoswitchable compound and without genetic manipulation. The molecule, named PAI, was designed by introduction of a photoswitch into the molecular structure of an M2 mAChR agonist. In vitro assays revealed that PAI enables light-dependent activation of M2 mAChRs. To validate the method, we show that PAI photoisomers display different cardiac effects in a mammalian animal model, and demonstrate reversible, real-time photocontrol of cardiac function in translucent wildtype tadpoles. PAI can also effectively activate M2 receptors using two-photon excitation with near-infrared light, which overcomes the scattering and low penetration of short-wavelength illumination, and offers new opportunities for intravital imaging and control of cardiac function.

The loss of ecosystem-services emerging from artificial light at night

ABSTRACTLight pollution is increasing worldwide, affecting human health and ecosystem quality. The adverse effect of this novel pollution, mediated in mammals by suppression of the pineal neuro-hormone melatonin production and secretion, particularly by short wavelength (SWL) illumination. Currently, this problem is not challenged sufficiently, even ignored by decision-makers at local and national levels, as well as other related organizations. Therefore, we assume that the correct way to deal with it will be by treating the dark night as an ecosystem-service for temporal organization of humans as other organisms. Therefore, chasing darkness away and mainly by SWL illumination is as giving up the natural light/dark cycles offered as an ecosystem-service. So far, we have no environmental economic tools for assessing the real coast of the health damages or reduction in pollination caused by light pollution. Using Artificial Light at Night (ALAN) as a loss of ecosystem-services will enable us to give it a realistic economic value thus an opportunity to re-evaluate the environmental cost of SWL efficient illumination. This will also help decision-makers to move to the next stage of illumination preferring sustainable illumination.

Thermal nanoimprint lithography for drift correction in super-resolution fluorescence microscopy.

Localization-based super-resolution microscopy enables imaging of biological structures with sub-diffraction-limited accuracy, but generally requires extended acquisition time. Consequently, stage drift often limits the spatial precision. Previously, we reported a simple method to correct for this by creating an array of 1 μm3 fiducial markers, every ~8 μm, on the coverslip, using UV-nanoimprint lithography (UV-NIL). While this allowed reliable and accurate 3D drift correction, it suffered high autofluorescence background with shorter wavelength illumination, unstable adsorption to the substrate glass surface, and suboptimal biocompatibility. Here, we present an improved fiducial micro-pattern prepared by thermal nanoimprint lithography (T-NIL). The new pattern is made of a thermal plastic material with low fluorescence backgrounds across the wide excitation range, particularly in the blue-region; robust structural stability under cell culturing condition; and a high bio-compatibility in terms of cell viability and adhesion. We demonstrate drift precision to 1.5 nm for lateral (x, y) and 6.1 nm axial (z) axes every 0.2 seconds for a total of 1 min long image acquisition. As a proof of principle, we acquired 4-color wide-field fluorescence images of live mammalian cells; we also acquired super-resolution images of fixed hippocampal neurons, and super-resolution images of live glutamate receptors and postsynaptic density proteins.

A Novel Photodetector Based on Azo/SiO x /N-Si Heterojunction Structure

Recently, photodetector based on semiconductor-insulator-semiconductor (SIS) heterojunction structure which contains indium zinc oxide (IZO) as the transparent conductive oxide (TCO) layer was reported. In that work, IZO layer was deposited by pulsed laser deposition which is impractical to the large-area device production. Moreover, the IZO contains indium which becomes a scarce element due to the vast demand in solar cell and display industries in recent years. In order to overcome these difficulties, aluminum zinc oxide (AZO) was adopted to replace IZO as the TCO layer and the feasibility of AZO/SiO x /n-Si SIS structure to photodetection was investigated. The SIS structure was prepared firstly by growing SiO x layer with appropriate thickness (~1.8 nm) on n-type Si wafer substrate by dry thermal oxidation method. Radio-frequency sputtering was then adopted to deposit a 200-nm thick AZO layer on SiO x /Si substrate. Afterward, the 100-nm thick aluminum layers were deposited by e-beam evaporation to form the bottom electrodes on the backside of Si substrates and the top finger electrodes on AZO layer, respectively, to complete the SIS photodetector preparation. Without applying external bias, the sample with quick photo-response time less than 10 msec and photoresponse (R) of 0.17, 0.67 and 0.22 AW-1separately under the 365-nm, 650-nm and 940-nm illuminations were achieved. The lower R value at short-wavelength illumination was attributed to the absorption of AZO layer since the photon energy of incident light is close to the absorption edge of AZO. The sample was further annealed at 300°C for 1 hr in air ambient and the improvement of R values, 0.27, 1.60 and 0.67 AW-1 under the 365-nm, 650-nm and 940-nm illuminations, was observed. The improvement of R values of the device was ascribed to the reduction of interface trap density (Dit ) at the AZO/SiO x and SiO x /n-Si interfaces as revealed by the capacitance-voltage measurement. The annealing treatment reduced the Dit from 1.63×1012 to 2.80×1011 eV-1cm-2, which efficiently alleviated the carrier capture at interfaces and improved the photodetection properties of the sample. Keywords : Photodetector; Aluminum zinc oxide; Semiconductor-insulator-semiconductor heterojunction; interface trap density.

White-light vs. short-wavelength ultraviolet illumination of fingerprints developed with columnar thin films of Alq3

The deposition of a columnar thin film (CTF) of Alq3 on partial-bloody fingerprints has recently been shown to yield better development than many traditional development techniques. The Alq3-CTF-developed fingerprint is illuminated by short-wavelength ultraviolet (UV) light, to take advantage of the luminescence of Alq3. Experiments were undertaken to test the hypothesis that white-light illumination of Alq3-CTF-developed fingerprints is inferior to UV illumination. Objective and subjective grading of photographs of 18 Alq3-CTF-developed fingerprints on brass strongly indicate that white-light illumination is likely to be suitable for comparison; if that fails to yield a strong conclusion, then a photograph taken with short-wavelength UV illumination should be examined by a human. This procedure would reduce not only UV-induced health hazards in the laboratory but also the chance of denaturing potentially useful DNA information contained in the fingerprint.

Fractional Talbot lithography with extreme ultraviolet light.

Fractional Talbot effect leads to the possibility to implement patterning of structures with smaller periods than the master mask. This is particularly attractive when using short wavelength illumination in the extreme ultraviolet because of attainable resolution in the sub-100-nm range. In this Letter, we demonstrate the Talbot lithography with the fractional Talbot effect under coherent illumination generated with a capillary discharge Ne-like Ar extreme ultraviolet laser. Various spatial frequency multiplications up to 5x are achieved using a parent grating. This technique allows a fabrication of nanostructures with high-resolution patterns, which is of high interest in many applications such as the manufacturing of plasmonic surfaces and photonic devices.

The optical properties of single-crystal silicon in the 3–5-µm region

This paper discusses features of radiation absorption in the spectral region from 3 to 5 µm by single-crystal silicon: the dependence of the absorption coefficient on resistivity in samples of n- and p-type conductivity, the additional absorption associated with intraband electron transitions in the conduction band, and the influence of short-wavelength illumination on the transmission spectra. Recommendations for the use of silicon as an optical medium are given from an analysis of the calculated and experimental data.

Coaxial Group III−Nitride Nanowire Photovoltaics

Coaxial core/shell nanowires represent an important class of nanoscale building blocks with substantial potential for exploring new concepts and materials for solar energy conversion. Here, we report the first experimental realization of coaxial group III-nitride nanowire photovoltaic (PV) devices, n-GaN/i-In(x)Ga(1-x)N/p-GaN, where variation of indium mole fraction is used to control the active layer band gap and hence light absorption. Current-voltage data reveal clear diode characteristics with ideality factors from 3.9 to 5.6. Electroluminescence measurements demonstrate tunable emission from 556 to 371 nm and thus confirm band gap variations in the In(x)Ga(1-x)N active layer from 2.25 to 3.34 eV as In composition is varied. Simulated one-sun AM 1.5G illumination yielded open-circuit voltages (V(oc)) from 1.0 to 2.0 V and short-circuit current densities (J(sc)) from 0.39 to 0.059 mA/cm(2) as In composition is decreased from 0.27 to 0 and a maximum efficiency of approximately 0.19%. The n-GaN/i-In(x)Ga(1-x)N/p-GaN nanowire devices are highly robust and exhibit enhanced efficiencies for concentrated solar light illuminations as well as single nanowire J(sc) values as high as 390 mA/cm(2) under intense short-wavelength illumination. The ability to rationally tune the structure and composition of these core/shell III-nitride nanowires will make them a powerful platform for exploring nanoenabled PVs in the future.

Multi-color LUCAS: Lensfree On-chip Cytometry Using Tunable Monochromatic Illumination and Digital Noise Reduction

It has been recently demonstrated that rapid on-chip monitoring of a homogenous cell solution within an ultra-large field-of-field of ~10 cm2 is feasible by recording the classical diffraction pattern of each cell in parallel onto an opto-electronic sensor array under incoherent white light illumination. Here we present several major improvements over this previous approach. First, through experimental results, we illustrate that the use of narrowband short wavelength illumination (e.g., at ~300 nm) significantly improves the digital signal-to-noise ratio of the cell diffraction signatures, which translates itself to a significant increase in the depth-of-field (e.g., ~5 mm) and hence the sample volume (e.g., 5 mL) that can be imaged. Second, we also illustrate that by varying the illumination wavelength, the texture of the recorded cell signatures can be tuned to enable automated identification and characterization of a target cell type within a heterogeneous cell solution. Third, a hybrid imaging scheme that combines two different wavelengths is also demonstrated to improve the uniformity and signal-to-noise ratio of the recorded cell diffraction images. Finally, we demonstrate that a further improvement in image quality can be achieved by utilizing adaptive digital filtering. These noteworthy improvements are especially quite important to achieve more reliable performance for rapid detection and counting of a target cell type among many other cells present within a heterogeneous sample volume of e.g., ~5 mL. This incoherent on-chip imaging platform may have a significant impact especially for medical diagnostic applications related to global health problems such as HIV monitoring.

Fleeing Overexposure

Locomotion in the nematode Caenorhabditis elegans depends on neuronal Gα q and Gα s signaling pathways involved in synaptic function. Thus, worms in which either of these signaling pathways are nonfunctional are virtually paralyzed. Edwards et al . found that exposure to blue-violet light restored coordinated locomotion to worms with loss-of-function mutations affecting either Gα q or Gα s signaling pathways. Only short-wavelength light was effective in eliciting locomotion, through a mechanism that did not depend on temperature change, with the maximal response occurring with exposure to ultraviolet light. Prolonged exposure to short-wavelength light was lethal, and, given the option, wild-type worms avoided short-wavelength illumination. A forward genetic screen for motile worms that lacked a locomotive response to short-wavelength light implicated a protein that the authors called LITE-1. Intriguingly, LITE-1 is unrelated to any known photoreceptor protein but instead resembles an insect Gustatory receptor (Gr) protein. When lite-1 was expressed in the neurons of lite-1 -null mutant worms, it restored light-induced locomotion; when heterologously expressed in body wall and egg-laying muscles, it elicited light-induced contraction and egg expulsion. Thus, the authors conclude that LITE-1 represents a photoreceptor for ultraviolet light that may allow C. elegans to avoid lethal exposure to sunlight. S. L. Edwards, N. K. Charlie, M. C. Milfort, B. S. Brown, C. N. Gravlin, J. E. Knecht, K. G. Miller, A novel molecular solution for ultraviolet light detection in Caenorhabditis elegans . PLoS Biol. 6 , e198 (2008). [PubMed]