Flat metaoptics components are looking to replace classical optics elements and could lead to ext... more Flat metaoptics components are looking to replace classical optics elements and could lead to extremely compact biophotonics devices if integrated with on-chip light sources and detectors. However, using metasurfaces to shape light into wide angular range wavefronts with high efficiency, as is typically required in high-contrast microscopy applications, remains a challenge. Here we demonstrate curved GaAs metagratings integrated on vertical-cavity surface-emitting lasers (VCSELs) that enable on-chip illumination in total internal reflection and dark field microscopy. Based on an unconventional design that circumvents the aspect ratio dependent etching problems in monolithic integration, we demonstrate off-axis emission centred at 60° in air and 63° in glass with > 90% and > 70% relative deflection efficiency, respectively. The resulting laser beam is collimated out-of-plane but maintains Gaussian divergence in-plane, resulting in a long and narrow illumination area. We show th...
luorescence microscopy has been a long-standing workhorse in biochemistry and biophysics 1-5. How... more luorescence microscopy has been a long-standing workhorse in biochemistry and biophysics 1-5. However, a key limitation is the need for labeling with fluorescent tags. Therefore, one current research frontier is the development of methods that enable label-free studies of single biological nanoparticles (BNPs) and biomolecules to complement fluorescence-based techniques. Label-free methods bypass the following limitations of fluorescence microscopy: (1) attaching a fluorescent label to a target may alter its properties 6,7 ; (2) there is a limited number of label colors that can be used simultaneously; and (3) long-term measurements are complicated by photobleaching. In addition, in cell-secretion-related studies 8 , it is very difficult to specifically label biomolecules of interest and, most importantly, it is only possible to detect predefined labeled secreted entities, which means unlabeled but potentially important entities are probably overlooked. Label-free single-biomolecule detection has been enabled recently by dielectric microresonators 9 , plasmonic approaches based on metallic continuous films 10 and nanostructures 11 , and interferometric scattering microscopy (iSCAT) 12-16. iSCAT has been used to investigate, for example, single cell secretion dynamics 13 and protein motion on a dielectric substrate 14 , on a supported lipid bilayer 17,18 or on actin filaments 15. Furthermore, in contrast to alternative methods, iSCAT enables quantitative molecular weight (MW) measurements of biomolecules, since the signal intensity is proportional to the weight of the imaged object 12,16. However, and as a key point, these three label-free optical single-molecule detection methods require the investigated species to bind to a surface to be "visible". This requirement can lead to misinterpretations when applied to biomolecular interaction studies because binding to a surface may affect the properties and accessibility of molecular binding sites 19. In addition, binding is a selective process, meaning that only molecules that actually bind are detected, while a large fraction remains unseen. Consequently, the ability to label-free image and track diffusing single biomolecules directly in solution would constitute an important step in the field. However, the resolution of current state-of-the-art microscopy techniques allows imaging only of much larger diffusing objects, such as viruses 20 , extracellular vesicles 21 (EVs), or dielectric particles 22. This is mainly because the scattering cross-section of individual biomolecules is very small, preventing their direct detection, and because their fast Brownian motion permits the accumulation of the light they scatter only for the extremely short time they spend in a diffraction limited spot and/or before they diffuse out of the focal plane. To overcome these limitations, we present NSM, which enables the real-time label-free imaging of single BNPs and biomolecules in solution down to the few tens of kilo-Daltons regime inside a nanofluidic channel, without the need for surface immobilization. Furthermore, it allows the simultaneous determination of MW from the optical contrast of the imaged nano-object, and of its hydrodynamic radius (R s) and/or conformational state from the measured diffusivity. Results Nanofluidic scattering microscopy. NSM works by imaging nanofluidic channels nanofabricated into an optically transparent matrix, such as SiO 2 , by dark-field light-scattering microscopy (Fig. 1a). The channel cross-sectional dimensions can range from tens to hundreds of nanometers, depending on the size of the investigated
Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ul... more Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.
In developing micro- and nanodevices, stiction between their parts, that is, static friction prev... more In developing micro- and nanodevices, stiction between their parts, that is, static friction preventing surfaces in contact from moving, is a well-known problem. It is caused by the finite-temperature analogue of the quantum electrodynamical Casimir–Lifshitz forces, which are normally attractive. Repulsive Casimir–Lifshitz forces have been realized experimentally, but their reliance on specialized materials severely limits their applicability and prevents their dynamic control. Here we demonstrate that repulsive critical Casimir forces, which emerge in a critical binary liquid mixture upon approaching the critical temperature, can be used to counteract stiction due to Casimir–Lifshitz forces and actively control microscopic and nanoscopic objects with nanometre precision. Our experiment is conducted on a microscopic gold flake suspended above a flat gold-coated substrate immersed in a critical binary liquid mixture. This may stimulate the development of micro- and nanodevices by pre...
BackgroundA wide variety of photosynthetic and non-photosynthetic species sense and respond to li... more BackgroundA wide variety of photosynthetic and non-photosynthetic species sense and respond to light, having developed protective mechanisms to adapt to damaging effects on DNA and proteins. While the biology of UV light-induced damage has been well studied, cellular responses to stress from visible light (400–700 nm) remain poorly understood despite being a regular part of the life cycle of many organisms. Here, we developed a high-throughput method for measuring growth under visible light stress and used it to screen for light sensitivity in the yeast gene deletion collection.ResultsWe found genes involved in HOG pathway signaling, RNA polymerase II transcription, translation, diphthamide modifications of the translational elongation factor eEF2, and the oxidative stress response to be required for light resistance. Reduced nuclear localization of the transcription factor Msn2 and lower glycogen accumulation indicated higher protein kinase A (cAMP-dependent protein kinase, PKA) ac...
Phase-gradient metasurfaces have the potential to revolutionize photonics by offering ultrathin a... more Phase-gradient metasurfaces have the potential to revolutionize photonics by offering ultrathin alternatives to a wide range of common optical elements, including bulky refractive optics, waveplates, and axicons. However, the fabrication of stateof-the-art metasurfaces typically involves several expensive, timeconsuming, and potentially hazardous processing steps. To address this limitation, a facile methodology to construct phase-gradient metasurfaces from an exposed standard electron beam resist is developed. The method dramatically cuts the required processing time and cost as well as reduces safety hazards. The advantages of the method are demonstrated by constructing high-performance flat optics based on the Pancharatnam-Berry phase gradient concept for the entire visible wavelength range. Manufactured devices include macroscopic (1 cm diameter) positive lenses, gratings exhibiting anomalous reflection, and cylindrical metalenses on flexible plastic substrates.
Plasmonic optical antennas and metamaterials with an ability to boost light-matter interactions f... more Plasmonic optical antennas and metamaterials with an ability to boost light-matter interactions for particular incidence or emission angles could find widespread use in solar harvesting, biophotonics, and in improving photon source performance at optical frequencies. However, directional plasmonic structures have generally large footprints or require complicated geometries and costly nanofabrication technologies. Here, we present a directional metasurface realized by breaking the out-of-plane symmetry of its individual elements: tilted subwavelength plasmonic gold nanopillars. Directionality is caused by the complex charge oscillation induced in each individual nanopillar, which essentially acts as a tilted dipole above a dielectric interface. The metasurface is homogeneous over a macroscopic area and it is fabricated by a combination of facile colloidal lithography and off-normal metal deposition. Fluorescence excitation and emission from dye molecules deposited on the metasurface is enhanced in specific directions determined by the tilt angle of the nanopillars. We envisage that these directional metasurfaces can be used as cost-effective substrates for surface-enhanced spectroscopies and a variety of nanophotonic applications.
Three-dimensional chiral plasmonic nanostructures have been shown to be able to dramatically boos... more Three-dimensional chiral plasmonic nanostructures have been shown to be able to dramatically boost photon-spin selective light-matter interactions, potentially leading to novel photonics, molecular spectroscopy, and light-harvesting applications based on circularly polarized light. Here, we show that chiral split-ring gold nanoresonators interfaced to a wide band gap semiconductor exhibit a contrast in hot-electron transfer rate between left-handed and right-handed visible light that essentially mimics the far-field circular dichroism of the structures. We trace down the origin of this effect to the differential excitation of the thinnest part of the split-ring structures using dichroic-sensitive cathodoluminescence imaging with nanometer spatial resolution. The results highlight the intricate interplay between the near-field and far-field chiral response of a nanostructure and establishes a clear link to the emerging field of hot carrier plasmonics with numerous potential applicati...
Optics and Photonics Society of Iran, Mar 15, 2015
Optical tweezers have become powerful tools in many areas. By transferring light momentum from ph... more Optical tweezers have become powerful tools in many areas. By transferring light momentum from photons to micro-and nano-particles, one could immobilize submicron particles, transport them and also measure sub-picoNewton forces. In this paper we show by utilizing the angular momentum of a circularly polarized light, metallic nano particles rotate. Rotation speed depends to laser power and particle shape and size. Here, we show that rotation speed for round shape particle raise up to few kHz.
The phonon Raman spectra of Bi 2 Sr 2 Ca 1Ϫx Y x Cu 2 O 8ϩd (xϭ0Ϫ1) have been investigated in a n... more The phonon Raman spectra of Bi 2 Sr 2 Ca 1Ϫx Y x Cu 2 O 8ϩd (xϭ0Ϫ1) have been investigated in a number of well-defined single-crystal and polycrystalline samples. From the polarization and Y-doping dependence, and from a comparison with previous reports on Bi-based cuprates, we identify the (6A 1g ϩ1B 1g) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. A large number of extra ''disorder-induced'' phonon bands are observed in the ab-plane polarized spectra. In contrast to most previous reports, we argue that the c-axis polarized phonon band around 629 cm Ϫ1 is due to the O͑2͒ Sr A 1g vibration, while the exclusively ab-plane polarized band around 463 cm Ϫ1 is induced by the O͑3͒ Bi A 1g vibration. With increasing Y doping we find that the vibrational modes involving atoms in the CuO 2 planes rapidly increase in intensity as a result of the reduced metallic screening in the hole-depleted Y-doped samples. We also find that Y substitution gives rise to a substantial hardening of the O͑1͒ Cu A 1g and B 1g phonons by ϳ40 cm Ϫ1 , whereas the O͑2͒ Sr A 1g phonon is found to soften by ϳ20 cm Ϫ1 , when x increases from 0 to 1. The phonon frequency changes can be explained by the ''internal pressure'' induced by the decrease in the average Ca/Y ion size and an additional ''charge-transfer'' induced by the change in the Cu and Bi valences with Y doping.
Threats from chemical warfare agents, commonly known as nerve gases, constitute a serious securit... more Threats from chemical warfare agents, commonly known as nerve gases, constitute a serious security issue of increasing global concern because of surging terrorist activity worldwide. However, nerve gases are difficult to detect using current analytical tools and outside dedicated laboratories. Here we demonstrate that surface-enhanced Raman scattering (SERS) can be used for sensitive detection of femtomol quantities of two nerve gases, VX and Tabun, using a handheld Raman device and SERS substrates consisting of flexible gold-covered Si nanopillars. The substrate surface exhibits high droplet adhesion and nanopillar clustering due to elasto-capillary forces, resulting in enrichment of target molecules in plasmonic hot-spots with high Raman enhancement. The results may pave the way for strategic life-saving SERS detection of chemical warfare agents in the field.
The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructu... more The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been a subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be realized in plasmonic pentamers constructed from metal−insulator− metal (MIM) sandwich particles. Each MIM unit acts as a magnetic meta-atom and the optical magnetism is rendered quasi-broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamers exhibit multiple Fano resonances and a broad subradiant spectral window that signals the magnetic interaction and a hierarchy of coupling effects in these intricate three-dimensional nanoparticle oligomers.
The resonance behavior of the oxygen breathing mode at 700 cm(-1) and its higher orders is studie... more The resonance behavior of the oxygen breathing mode at 700 cm(-1) and its higher orders is studied between 1.8 eV (676 nm) and 4.2 eV (300 nm) in the perovskite LaFe(0.5)Cr(0.5)O(3). The Franck-Condon induced higher order scattering present in the x=0.1, 0.5 and 0.9 compounds dominates the Raman spectrum in the visible energy region while a feature in the 1400 cm −1 energy region dominates using UV lasers. The energy location of this peak coincides both with the second order Franck-Condon mode as well as similar feature seen in the x=0 and 1 compounds (and to some extent in the low doping compounds (x=0.02, 0.04, 0.06 and 0.08)) using the 2.41 eV (λ=514) laser, believed to be a two-magnon caused by a spin-flip excitation in the AFM spin-state. Thus the complex magnetism in the Fe/Cr perovskite is likely to be influenced by the competition between the magnetically ordered state and the lattice dynamics through the resonant Franck-Condon effect.
High energy x-ray diffraction is used to investigate the bulk oxygen ordering properties of YBa_2... more High energy x-ray diffraction is used to investigate the bulk oxygen ordering properties of YBa_2Cu_3O_{6+x}. Superstructures of Cu-O chains aligned along the b axis and ordered with periodicity ma, along the a axis have been observed. For $x < 0.62$ the only observed superstructure is ortho-II with m=2. At room temperature we find ortho-III (m=3) for $0.72\le x\le 0.82$, ortho-V
High-energy x-ray diffraction is used to investigate the bulk oxygen-ordering properties of YBa 2... more High-energy x-ray diffraction is used to investigate the bulk oxygen-ordering properties of YBa 2 Cu 3 O 6ϩx. Four different superstructures of Cu-O chains aligned along the b axis and ordered with periodicity ma, along the a axis have been observed. For xϽ0.62, the only observed superstructure is ortho-II with mϭ2. At room temperature, we find ortho-III (mϭ3) for 0.72рxр0.82, ortho-V (mϭ5) in a mixed state with ortho-II at xϭ0.62, and ortho-VIII (mϭ8) at xϭ0.67. Ortho-II is a three-dimensional ordered structural phase, the remaining ones are essentially two-dimensional. None of the superstructures develops long-range ordering. The temperature dependence of the observed superstructure ordering is investigated explicitly and a structural phase diagram is presented.
Raman measurements in YBa 2 Cu 3 O x (xϭ6.72-6.82͒ high-T c superconductors reveal intense phonon... more Raman measurements in YBa 2 Cu 3 O x (xϭ6.72-6.82͒ high-T c superconductors reveal intense phonon scattering due to an electronic resonance localized near oxygen vacancies on the CuO chains. Below room temperature the resonance can be photobleached in a manner similar to reported persistent photoinduced superconductivity effects, indicating photon-assisted oxygen ordering or electron vacancy capture. By comparing Raman and x-ray diffraction data we establish a correlation between the stability of the photoinduced state and the oxygen-ordering kinetics in the CuO chains. ͓S0163-1829͑98͒50222-6͔ RAPID COMMUNICATIONS
Light in the visible range can be stressful to non-photosynthetic organisms. The yeast Saccharomy... more Light in the visible range can be stressful to non-photosynthetic organisms. The yeast Saccharomyces cerevisiae has earlier been reported to respond to blue light via activation of the stress-regulated transcription factor Msn2p. Environmental changes also induce activation of calcineurin, a Ca 2+ /calmodulin dependent phosphatase, which in turn controls gene transcription by dephosphorylating the transcription factor Crz1p. We investigated the connection between cellular stress caused by blue light and Ca 2+ signalling in yeast by monitoring the nuclear localization dynamics of Crz1p, Msn2p and Msn4p. The three proteins exhibit distinctly different stress responses in relation to light exposure. Msn2p, and to a lesser degree Msn4p, oscillate rapidly between the nucleus and the cytoplasm in an apparently stochastic fashion. Crz1p, in contrast, displays a rapid and permanent nuclear localization induced by illumination, which triggers Crz1p-dependent transcription of its target gene CMK2. Moreover, increased extracellular Ca 2+ levels stimulates the light-induced responses of all three transcription factors, e.g. Crz1p localizes much quicker to the nucleus and a larger fraction of cells exhibits permanent Msn2p nuclear localization at higher Ca 2+ concentration. Studies in mutants lacking Ca 2+ transporters indicate that influx of extracellular Ca 2+ is crucial for the initial stages of light-induced Crz1p nuclear localization, while mobilization of intracellular Ca 2+ stores appears necessary for a sustained response. Importantly, we found that Crz1p nuclear localization is dependent on calcineurin and the carrier protein Nmd5p, while not being affected by increased protein kinase A activity (PKA), which strongly inhibits light-induced nuclear localization of Msn2/4p. We conclude that the two central signalling pathways, cAMP-PKA-Msn2/4 and Ca 2+-calcineurin-Crz1, are both activated by blue light illumination.
Submitted for the MAR10 Meeting of The American Physical Society Calculations of optical properti... more Submitted for the MAR10 Meeting of The American Physical Society Calculations of optical properties of nanohole systems in metallic films PETER JOHANSSON, Orebro University, VLADIMIR MILJKOVIC, MIKAEL KALL, Chalmers University-We present a computational study of the optical properties of systems of nanohole system in thin (the typical thickness is less than 100 nm) noble metal films. The Green's tensor technique adopted to layered systems forms the analytical framework to the calculations. We have studied individual holes as well as several interacting holes, and calculated quantities related both to far-field properties such as scattering cross sections and near fields and nearfield properties such as resonance energy transfer between molecules. The resonance properties of nanoholes are determined by their size and shape[1]. The interaction between two holes can, at a basic level, be understood as a dipole-dipole interaction between the holes, however, the interaction strength is strongly modulated by the properties of the surface plasmons of the metal film[2]. [1]. B.
... Thomas Härtling,* † Yury Alaverdyan, ‡ § Marc Tobias Wenzel, † René Kullock, † Mikael Käll, ‡... more ... Thomas Härtling,* † Yury Alaverdyan, ‡ § Marc Tobias Wenzel, † René Kullock, † Mikael Käll, ‡ and Lukas M. Eng †. Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany, Department ...
Flat metaoptics components are looking to replace classical optics elements and could lead to ext... more Flat metaoptics components are looking to replace classical optics elements and could lead to extremely compact biophotonics devices if integrated with on-chip light sources and detectors. However, using metasurfaces to shape light into wide angular range wavefronts with high efficiency, as is typically required in high-contrast microscopy applications, remains a challenge. Here we demonstrate curved GaAs metagratings integrated on vertical-cavity surface-emitting lasers (VCSELs) that enable on-chip illumination in total internal reflection and dark field microscopy. Based on an unconventional design that circumvents the aspect ratio dependent etching problems in monolithic integration, we demonstrate off-axis emission centred at 60° in air and 63° in glass with > 90% and > 70% relative deflection efficiency, respectively. The resulting laser beam is collimated out-of-plane but maintains Gaussian divergence in-plane, resulting in a long and narrow illumination area. We show th...
luorescence microscopy has been a long-standing workhorse in biochemistry and biophysics 1-5. How... more luorescence microscopy has been a long-standing workhorse in biochemistry and biophysics 1-5. However, a key limitation is the need for labeling with fluorescent tags. Therefore, one current research frontier is the development of methods that enable label-free studies of single biological nanoparticles (BNPs) and biomolecules to complement fluorescence-based techniques. Label-free methods bypass the following limitations of fluorescence microscopy: (1) attaching a fluorescent label to a target may alter its properties 6,7 ; (2) there is a limited number of label colors that can be used simultaneously; and (3) long-term measurements are complicated by photobleaching. In addition, in cell-secretion-related studies 8 , it is very difficult to specifically label biomolecules of interest and, most importantly, it is only possible to detect predefined labeled secreted entities, which means unlabeled but potentially important entities are probably overlooked. Label-free single-biomolecule detection has been enabled recently by dielectric microresonators 9 , plasmonic approaches based on metallic continuous films 10 and nanostructures 11 , and interferometric scattering microscopy (iSCAT) 12-16. iSCAT has been used to investigate, for example, single cell secretion dynamics 13 and protein motion on a dielectric substrate 14 , on a supported lipid bilayer 17,18 or on actin filaments 15. Furthermore, in contrast to alternative methods, iSCAT enables quantitative molecular weight (MW) measurements of biomolecules, since the signal intensity is proportional to the weight of the imaged object 12,16. However, and as a key point, these three label-free optical single-molecule detection methods require the investigated species to bind to a surface to be "visible". This requirement can lead to misinterpretations when applied to biomolecular interaction studies because binding to a surface may affect the properties and accessibility of molecular binding sites 19. In addition, binding is a selective process, meaning that only molecules that actually bind are detected, while a large fraction remains unseen. Consequently, the ability to label-free image and track diffusing single biomolecules directly in solution would constitute an important step in the field. However, the resolution of current state-of-the-art microscopy techniques allows imaging only of much larger diffusing objects, such as viruses 20 , extracellular vesicles 21 (EVs), or dielectric particles 22. This is mainly because the scattering cross-section of individual biomolecules is very small, preventing their direct detection, and because their fast Brownian motion permits the accumulation of the light they scatter only for the extremely short time they spend in a diffraction limited spot and/or before they diffuse out of the focal plane. To overcome these limitations, we present NSM, which enables the real-time label-free imaging of single BNPs and biomolecules in solution down to the few tens of kilo-Daltons regime inside a nanofluidic channel, without the need for surface immobilization. Furthermore, it allows the simultaneous determination of MW from the optical contrast of the imaged nano-object, and of its hydrodynamic radius (R s) and/or conformational state from the measured diffusivity. Results Nanofluidic scattering microscopy. NSM works by imaging nanofluidic channels nanofabricated into an optically transparent matrix, such as SiO 2 , by dark-field light-scattering microscopy (Fig. 1a). The channel cross-sectional dimensions can range from tens to hundreds of nanometers, depending on the size of the investigated
Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ul... more Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.
In developing micro- and nanodevices, stiction between their parts, that is, static friction prev... more In developing micro- and nanodevices, stiction between their parts, that is, static friction preventing surfaces in contact from moving, is a well-known problem. It is caused by the finite-temperature analogue of the quantum electrodynamical Casimir–Lifshitz forces, which are normally attractive. Repulsive Casimir–Lifshitz forces have been realized experimentally, but their reliance on specialized materials severely limits their applicability and prevents their dynamic control. Here we demonstrate that repulsive critical Casimir forces, which emerge in a critical binary liquid mixture upon approaching the critical temperature, can be used to counteract stiction due to Casimir–Lifshitz forces and actively control microscopic and nanoscopic objects with nanometre precision. Our experiment is conducted on a microscopic gold flake suspended above a flat gold-coated substrate immersed in a critical binary liquid mixture. This may stimulate the development of micro- and nanodevices by pre...
BackgroundA wide variety of photosynthetic and non-photosynthetic species sense and respond to li... more BackgroundA wide variety of photosynthetic and non-photosynthetic species sense and respond to light, having developed protective mechanisms to adapt to damaging effects on DNA and proteins. While the biology of UV light-induced damage has been well studied, cellular responses to stress from visible light (400–700 nm) remain poorly understood despite being a regular part of the life cycle of many organisms. Here, we developed a high-throughput method for measuring growth under visible light stress and used it to screen for light sensitivity in the yeast gene deletion collection.ResultsWe found genes involved in HOG pathway signaling, RNA polymerase II transcription, translation, diphthamide modifications of the translational elongation factor eEF2, and the oxidative stress response to be required for light resistance. Reduced nuclear localization of the transcription factor Msn2 and lower glycogen accumulation indicated higher protein kinase A (cAMP-dependent protein kinase, PKA) ac...
Phase-gradient metasurfaces have the potential to revolutionize photonics by offering ultrathin a... more Phase-gradient metasurfaces have the potential to revolutionize photonics by offering ultrathin alternatives to a wide range of common optical elements, including bulky refractive optics, waveplates, and axicons. However, the fabrication of stateof-the-art metasurfaces typically involves several expensive, timeconsuming, and potentially hazardous processing steps. To address this limitation, a facile methodology to construct phase-gradient metasurfaces from an exposed standard electron beam resist is developed. The method dramatically cuts the required processing time and cost as well as reduces safety hazards. The advantages of the method are demonstrated by constructing high-performance flat optics based on the Pancharatnam-Berry phase gradient concept for the entire visible wavelength range. Manufactured devices include macroscopic (1 cm diameter) positive lenses, gratings exhibiting anomalous reflection, and cylindrical metalenses on flexible plastic substrates.
Plasmonic optical antennas and metamaterials with an ability to boost light-matter interactions f... more Plasmonic optical antennas and metamaterials with an ability to boost light-matter interactions for particular incidence or emission angles could find widespread use in solar harvesting, biophotonics, and in improving photon source performance at optical frequencies. However, directional plasmonic structures have generally large footprints or require complicated geometries and costly nanofabrication technologies. Here, we present a directional metasurface realized by breaking the out-of-plane symmetry of its individual elements: tilted subwavelength plasmonic gold nanopillars. Directionality is caused by the complex charge oscillation induced in each individual nanopillar, which essentially acts as a tilted dipole above a dielectric interface. The metasurface is homogeneous over a macroscopic area and it is fabricated by a combination of facile colloidal lithography and off-normal metal deposition. Fluorescence excitation and emission from dye molecules deposited on the metasurface is enhanced in specific directions determined by the tilt angle of the nanopillars. We envisage that these directional metasurfaces can be used as cost-effective substrates for surface-enhanced spectroscopies and a variety of nanophotonic applications.
Three-dimensional chiral plasmonic nanostructures have been shown to be able to dramatically boos... more Three-dimensional chiral plasmonic nanostructures have been shown to be able to dramatically boost photon-spin selective light-matter interactions, potentially leading to novel photonics, molecular spectroscopy, and light-harvesting applications based on circularly polarized light. Here, we show that chiral split-ring gold nanoresonators interfaced to a wide band gap semiconductor exhibit a contrast in hot-electron transfer rate between left-handed and right-handed visible light that essentially mimics the far-field circular dichroism of the structures. We trace down the origin of this effect to the differential excitation of the thinnest part of the split-ring structures using dichroic-sensitive cathodoluminescence imaging with nanometer spatial resolution. The results highlight the intricate interplay between the near-field and far-field chiral response of a nanostructure and establishes a clear link to the emerging field of hot carrier plasmonics with numerous potential applicati...
Optics and Photonics Society of Iran, Mar 15, 2015
Optical tweezers have become powerful tools in many areas. By transferring light momentum from ph... more Optical tweezers have become powerful tools in many areas. By transferring light momentum from photons to micro-and nano-particles, one could immobilize submicron particles, transport them and also measure sub-picoNewton forces. In this paper we show by utilizing the angular momentum of a circularly polarized light, metallic nano particles rotate. Rotation speed depends to laser power and particle shape and size. Here, we show that rotation speed for round shape particle raise up to few kHz.
The phonon Raman spectra of Bi 2 Sr 2 Ca 1Ϫx Y x Cu 2 O 8ϩd (xϭ0Ϫ1) have been investigated in a n... more The phonon Raman spectra of Bi 2 Sr 2 Ca 1Ϫx Y x Cu 2 O 8ϩd (xϭ0Ϫ1) have been investigated in a number of well-defined single-crystal and polycrystalline samples. From the polarization and Y-doping dependence, and from a comparison with previous reports on Bi-based cuprates, we identify the (6A 1g ϩ1B 1g) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. A large number of extra ''disorder-induced'' phonon bands are observed in the ab-plane polarized spectra. In contrast to most previous reports, we argue that the c-axis polarized phonon band around 629 cm Ϫ1 is due to the O͑2͒ Sr A 1g vibration, while the exclusively ab-plane polarized band around 463 cm Ϫ1 is induced by the O͑3͒ Bi A 1g vibration. With increasing Y doping we find that the vibrational modes involving atoms in the CuO 2 planes rapidly increase in intensity as a result of the reduced metallic screening in the hole-depleted Y-doped samples. We also find that Y substitution gives rise to a substantial hardening of the O͑1͒ Cu A 1g and B 1g phonons by ϳ40 cm Ϫ1 , whereas the O͑2͒ Sr A 1g phonon is found to soften by ϳ20 cm Ϫ1 , when x increases from 0 to 1. The phonon frequency changes can be explained by the ''internal pressure'' induced by the decrease in the average Ca/Y ion size and an additional ''charge-transfer'' induced by the change in the Cu and Bi valences with Y doping.
Threats from chemical warfare agents, commonly known as nerve gases, constitute a serious securit... more Threats from chemical warfare agents, commonly known as nerve gases, constitute a serious security issue of increasing global concern because of surging terrorist activity worldwide. However, nerve gases are difficult to detect using current analytical tools and outside dedicated laboratories. Here we demonstrate that surface-enhanced Raman scattering (SERS) can be used for sensitive detection of femtomol quantities of two nerve gases, VX and Tabun, using a handheld Raman device and SERS substrates consisting of flexible gold-covered Si nanopillars. The substrate surface exhibits high droplet adhesion and nanopillar clustering due to elasto-capillary forces, resulting in enrichment of target molecules in plasmonic hot-spots with high Raman enhancement. The results may pave the way for strategic life-saving SERS detection of chemical warfare agents in the field.
The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructu... more The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been a subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be realized in plasmonic pentamers constructed from metal−insulator− metal (MIM) sandwich particles. Each MIM unit acts as a magnetic meta-atom and the optical magnetism is rendered quasi-broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamers exhibit multiple Fano resonances and a broad subradiant spectral window that signals the magnetic interaction and a hierarchy of coupling effects in these intricate three-dimensional nanoparticle oligomers.
The resonance behavior of the oxygen breathing mode at 700 cm(-1) and its higher orders is studie... more The resonance behavior of the oxygen breathing mode at 700 cm(-1) and its higher orders is studied between 1.8 eV (676 nm) and 4.2 eV (300 nm) in the perovskite LaFe(0.5)Cr(0.5)O(3). The Franck-Condon induced higher order scattering present in the x=0.1, 0.5 and 0.9 compounds dominates the Raman spectrum in the visible energy region while a feature in the 1400 cm −1 energy region dominates using UV lasers. The energy location of this peak coincides both with the second order Franck-Condon mode as well as similar feature seen in the x=0 and 1 compounds (and to some extent in the low doping compounds (x=0.02, 0.04, 0.06 and 0.08)) using the 2.41 eV (λ=514) laser, believed to be a two-magnon caused by a spin-flip excitation in the AFM spin-state. Thus the complex magnetism in the Fe/Cr perovskite is likely to be influenced by the competition between the magnetically ordered state and the lattice dynamics through the resonant Franck-Condon effect.
High energy x-ray diffraction is used to investigate the bulk oxygen ordering properties of YBa_2... more High energy x-ray diffraction is used to investigate the bulk oxygen ordering properties of YBa_2Cu_3O_{6+x}. Superstructures of Cu-O chains aligned along the b axis and ordered with periodicity ma, along the a axis have been observed. For $x < 0.62$ the only observed superstructure is ortho-II with m=2. At room temperature we find ortho-III (m=3) for $0.72\le x\le 0.82$, ortho-V
High-energy x-ray diffraction is used to investigate the bulk oxygen-ordering properties of YBa 2... more High-energy x-ray diffraction is used to investigate the bulk oxygen-ordering properties of YBa 2 Cu 3 O 6ϩx. Four different superstructures of Cu-O chains aligned along the b axis and ordered with periodicity ma, along the a axis have been observed. For xϽ0.62, the only observed superstructure is ortho-II with mϭ2. At room temperature, we find ortho-III (mϭ3) for 0.72рxр0.82, ortho-V (mϭ5) in a mixed state with ortho-II at xϭ0.62, and ortho-VIII (mϭ8) at xϭ0.67. Ortho-II is a three-dimensional ordered structural phase, the remaining ones are essentially two-dimensional. None of the superstructures develops long-range ordering. The temperature dependence of the observed superstructure ordering is investigated explicitly and a structural phase diagram is presented.
Raman measurements in YBa 2 Cu 3 O x (xϭ6.72-6.82͒ high-T c superconductors reveal intense phonon... more Raman measurements in YBa 2 Cu 3 O x (xϭ6.72-6.82͒ high-T c superconductors reveal intense phonon scattering due to an electronic resonance localized near oxygen vacancies on the CuO chains. Below room temperature the resonance can be photobleached in a manner similar to reported persistent photoinduced superconductivity effects, indicating photon-assisted oxygen ordering or electron vacancy capture. By comparing Raman and x-ray diffraction data we establish a correlation between the stability of the photoinduced state and the oxygen-ordering kinetics in the CuO chains. ͓S0163-1829͑98͒50222-6͔ RAPID COMMUNICATIONS
Light in the visible range can be stressful to non-photosynthetic organisms. The yeast Saccharomy... more Light in the visible range can be stressful to non-photosynthetic organisms. The yeast Saccharomyces cerevisiae has earlier been reported to respond to blue light via activation of the stress-regulated transcription factor Msn2p. Environmental changes also induce activation of calcineurin, a Ca 2+ /calmodulin dependent phosphatase, which in turn controls gene transcription by dephosphorylating the transcription factor Crz1p. We investigated the connection between cellular stress caused by blue light and Ca 2+ signalling in yeast by monitoring the nuclear localization dynamics of Crz1p, Msn2p and Msn4p. The three proteins exhibit distinctly different stress responses in relation to light exposure. Msn2p, and to a lesser degree Msn4p, oscillate rapidly between the nucleus and the cytoplasm in an apparently stochastic fashion. Crz1p, in contrast, displays a rapid and permanent nuclear localization induced by illumination, which triggers Crz1p-dependent transcription of its target gene CMK2. Moreover, increased extracellular Ca 2+ levels stimulates the light-induced responses of all three transcription factors, e.g. Crz1p localizes much quicker to the nucleus and a larger fraction of cells exhibits permanent Msn2p nuclear localization at higher Ca 2+ concentration. Studies in mutants lacking Ca 2+ transporters indicate that influx of extracellular Ca 2+ is crucial for the initial stages of light-induced Crz1p nuclear localization, while mobilization of intracellular Ca 2+ stores appears necessary for a sustained response. Importantly, we found that Crz1p nuclear localization is dependent on calcineurin and the carrier protein Nmd5p, while not being affected by increased protein kinase A activity (PKA), which strongly inhibits light-induced nuclear localization of Msn2/4p. We conclude that the two central signalling pathways, cAMP-PKA-Msn2/4 and Ca 2+-calcineurin-Crz1, are both activated by blue light illumination.
Submitted for the MAR10 Meeting of The American Physical Society Calculations of optical properti... more Submitted for the MAR10 Meeting of The American Physical Society Calculations of optical properties of nanohole systems in metallic films PETER JOHANSSON, Orebro University, VLADIMIR MILJKOVIC, MIKAEL KALL, Chalmers University-We present a computational study of the optical properties of systems of nanohole system in thin (the typical thickness is less than 100 nm) noble metal films. The Green's tensor technique adopted to layered systems forms the analytical framework to the calculations. We have studied individual holes as well as several interacting holes, and calculated quantities related both to far-field properties such as scattering cross sections and near fields and nearfield properties such as resonance energy transfer between molecules. The resonance properties of nanoholes are determined by their size and shape[1]. The interaction between two holes can, at a basic level, be understood as a dipole-dipole interaction between the holes, however, the interaction strength is strongly modulated by the properties of the surface plasmons of the metal film[2]. [1]. B.
... Thomas Härtling,* † Yury Alaverdyan, ‡ § Marc Tobias Wenzel, † René Kullock, † Mikael Käll, ‡... more ... Thomas Härtling,* † Yury Alaverdyan, ‡ § Marc Tobias Wenzel, † René Kullock, † Mikael Käll, ‡ and Lukas M. Eng †. Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany, Department ...
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Papers by Mikael Käll