Showing papers by "Olivier J. F. Martin published in 2016"
TL;DR: In this paper, a surface integral equation approach based on the tangential Poggio-Miller-Chang-Harrington-Wu-Tsai formulation was used to obtain a better understanding of the second-harmonic response of 3D plasmonic nanostructures.
Abstract: Using a surface integral equation approach based on the tangential Poggio–Miller–Chang–Harrington–Wu–Tsai formulation, we present a full wave analysis of the resonant modes of 3D plasmonic nanostructures. This method, combined with the evaluation of second-harmonic generation, is then used to obtain a better understanding of their nonlinear response. The second-harmonic generation associated with the fundamental dipolar modes of three distinct nanostructures (gold nanosphere, nanorod, and coupled nanoparticles) is computed in the same formalism and compared with the other computed modes, revealing the physical nature of the second-harmonic modes. The proposed approach provides a direct relationship between the fundamental and second-harmonic modes in complex plasmonic systems and paves the way for an optimal design of double resonant nanostructures with efficient nonlinear conversion. In particular, we show that the efficiency of second-harmonic generation can be dramatically increased when the modes with the appropriate symmetry are matched with the second-harmonic frequency.
56 citations
TL;DR: In this paper, the authors presented a method for Nanophotonics using plasmonics reference EPFL-reference EPFL and the Web of Science Record created on 2016-10-18.
Abstract: Keywords: Nanophotonics ; Plasmonics Reference EPFL-ARTICLE-221844doi:10.1002/adom.201500740View record in Web of Science Record created on 2016-10-18, modified on 2017-05-10
41 citations
TL;DR: In this paper, the second-harmonic generation (SHG) from gold split-ring resonators is investigated using different theoretical methods, namely, Miller's rule, the nonlinear effective susceptibility method, and full-wave computation based on a surface integral equation method.
Abstract: In this article, the second-harmonic generation (SHG) from gold split-ring resonators is investigated using different theoretical methods, namely, Miller’s rule, the nonlinear effective susceptibility method, and full-wave computation based on a surface integral equation method. The results confirm that Miller’s rule is, in general, not well suited for the description of SHG from plasmonic metasurfaces. On the other hand, the comparison of the nonlinear effective susceptibility method with full-wave computations shows that this method permits us to evaluate second-harmonic (SH) emission patterns from noncentrosymmetric nanoparticles with good accuracy. However, the nonlinear effective susceptibility method fails to reproduce the multipolar nature of the SH emission from centrosymmetric nanoparticles. This shortcoming is attributed to the intrinsic nature of the nonlinear effective susceptibility method, which neglects the exact positions of the nonlinear sources. The numerical implementations of these two methods are also discussed in detail, revealing that the main limitation of the nonlinear effective susceptibility method, aside from the inaccuracy observed in specific cases, is its higher numerical requirements when several emitting directions need to be considered. This limitation stands for most of the numerical methods used for solving Maxwell’s equations at the nanoscale. This work provides clear insight into the limitations and advantages of the different methods available for evaluation of SHG from plasmonic metasurfaces.
41 citations
TL;DR: In this paper, the second harmonic generation and two-photon photoluminescence have different behaviors despite the same expected fundamental intensity-dependence, and the underlying mechanisms explaining the differences between these two optical processes are investigated using a surface integral equation method for the nonlinear computations.
Abstract: In this article we compare the two-photon photoluminescence and second harmonic generation from single connected gold nanodimers. Analyzing the particle size-dependent nonlinear optical spectra and performing excitation polarization resolved measurements using an experimental setup combining a femtosecond laser source with a parabolic mirror, we show that second harmonic generation and two-photon photoluminescence have different behaviors despite the same expected fundamental intensity-dependence. For further understanding of the observed phenomena, the plasmon resonances of single nanodimers are investigated using dark-field optical microscopy, and calculations are performed with Green’s tensor method. Furthermore, the underlying mechanisms explaining the differences between these two optical processes are investigated using a surface integral equation method for the nonlinear computations. This study reveals that the different trends in the polarization-dependences of two-photon photoluminescence and se...
26 citations
TL;DR: A multi-layered microfluidic chip with an integrated optical sensor for the continuous sensitive detection of extracellular hydrogen peroxide (H2O2), one of the most stable ROS, is introduced.
Abstract: Reactive oxygen species (ROS) play an important role in the life of every cell, including cellular defense and signaling mechanisms. Continuous and quantitative ROS sensing can provide valuable information about the cell state, but it remains a challenge to measure. Here, we introduce a multi-layered microfluidic chip with an integrated optical sensor for the continuous sensitive detection of extracellular hydrogen peroxide (H2O2), one of the most stable ROS. This platform includes hydraulically controlled microvalves and microsieves, which enable the precise control of toxicants and complex exposure sequences. In particular, we use this platform to study the dynamics of toxicity-induced ROS generation in the green microalga Chlamydomonas reinhardtii during short-term exposures, recovery periods, and subsequent re-exposures. Two cadmium-based toxicants with distinct internalization mechanisms are used as stress inducers: CdSe/ZnS quantum dots (Qdots) and ionic cadmium (Cd(2+)). Our results show the quantitative dynamics of ROS generation by the model microalga, the recovery of cell homeostasis after stress events and the cumulative nature of two consecutive exposures. The dissolution of quantum dots and its possible influence on toxicity and H2O2 depletion is discussed. The obtained insights are relevant from ecotoxicological and physiological perspectives.
17 citations
TL;DR: The results emphasize the importance of the phase in the nonlinear optical processes arising in plasmonic nanostructures, in addition to the increase in conversion yield associated with the excitation of localized surface plAsmon resonances.
Abstract: We numerically investigate the second harmonic generation from different plasmonic systems and evidence the key role played in their nonlinear response by the phase at the fundamental wavelength. In the case of a single plasmonic nanorod, the interference between the second harmonic dipolar and quadrupolar emission modes depends on their relative phase, which is deeply related to the excitation wavelength. The knowledge obtained in this simple case is then used to describe and understand the nonlinear response from a more complex structure, namely a gold nanodolmen. The complex phase evolution associated with a Fano resonance arising at the fundamental wavelength enables dramatically modifying the second harmonic emission patterns from plasmonic metamolecules within minute wavelength shifts. These results emphasize the importance of the phase in the nonlinear optical processes arising in plasmonic nanostructures, in addition to the increase in conversion yield associated with the excitation of localized surface plasmon resonances.
17 citations
TL;DR: In this paper, the authors provide a pedagogical treatment of the complex nature of the polarisation charge and its relevance in plasmonics, and discuss how to understand and visualise them clearly using techniques such as phase correction and polarisation ellipse representation, to extract the underlying physical information.
Abstract: Polarisation charge formed on nanostructure surfaces upon optical excitation provides a useful tool to understand the underlying physics of plasmonic systems. Plasmonic simulations in the frequency domain typically calculate the polarisation charge as a complex quantity. In this paper, we provide a pedagogical treatment of the complex nature of the polarisation charge and its relevance in plasmonics, and discuss how naively extracting the real part of the complex quantities to obtain physical information can lead to pitfalls. We analyse the charge distributions on various plasmonic systems and explain how to understand and visualise them clearly using techniques such as phase-correction and polarisation ellipse representation, to extract the underlying physical information.
12 citations
TL;DR: It is demonstrated that a plasmonic nanodisk array can be utilized as a plAsmonic optical flat, with which nanometer-deep grooves can be directly visualized using a low-cost microscope.
Abstract: Two parallel optical surfaces often exhibit colorful fringes along the lines of equal thickness because of the interference of light. This simple phenomenon allows one to observe subwavelength corrugations on a reflective surface by simply placing on it a flat reference dielectric surface, a so-called optical flat, and inspecting the resultant interference pattern. In this work, we extend this principle from dielectric surfaces to two-dimensional plasmonic nanostructures. Optical couplings between an Au nanodisk array and an Au thin film were measured quantitatively using two different techniques, namely, the classical Newton’s rings method and a closed-loop nano-positioning system. Extremely high spectral sensitivity to the inter-surface distance was observed in the near-field coupling regime, where a 1-nm change in distance could alter the resonance wavelength by almost 10 nm, >40 times greater than the variation in the case without near-field coupling. With the help of a numerical fitting technique, the resonance wavelength could be determined with a precision of 0.03 nm, corresponding to a distance precision as high as 0.003 nm. Utilizing this effect, we demonstrated that a plasmonic nanodisk array can be utilized as a plasmonic optical flat, with which nanometer-deep grooves can be directly visualized using a low-cost microscope. By using an array of gold nanodisks as an optical flat, a team has shown that a normal microscope can image nanoscale grooves on surfaces. Optical interference between a reflective surface and a flat reference mirror (an optical flat) permits subwavelength corrugations on the surface to be imaged. Now, Weihua Zhang and co-workers at Nanjing University, China, with collaborators in Switzerland, have achieved high-resolution imaging of surface features by replacing the dielectric optical flat with a two-dimensional plasmonic nanostructure — a gold nanodisk array. They found that the resonance wavelength depends greatly on the gap between the surfaces. Specifically, a 1-nm change in distance can alter the resonance wavelength by almost 10 nm. The team is confident that this method will lead to rapid, low-cost, high-accuracy optical profiling of surfaces and high-precision machining.
11 citations
TL;DR: In this paper, it was shown that the second-harmonic generation intensity is directly related to the square of the absorbed power, which reproduces both the electric field enhancement and the specific size dependence of second-armonic generation in the small-particle limit.
Abstract: The optimization of nonlinear optical processes in plasmonic structures is important for the design of efficient nonlinear nanosources of light. Considering the simple case of spherical nanoparticles, we clearly identify the most efficient channel for second-harmonic generation, thanks to physical insights provided by the generalized Mie theory. This channel corresponds to the excitation of electric dipolar modes at the fundamental wavelength and a quadrupolar second-harmonic emission. Interestingly, it is demonstrated that the second-harmonic generation intensity is directly related to the square of the absorbed power, which reproduces both the electric field enhancement and the specific size dependence of second-harmonic generation in the small-particle limit. Additionally, the absorbed power can be optimized by controlling the nanoparticle size. These results demonstrate that the optimization of the fundamental electric field is not sufficient for reaching the highest nonlinear conversion in plasmonic ...
10 citations
TL;DR: Results showed that nano-TiO2 suspensions generated ROS under UV light (abiotic origin) and promoted ROS accumulation in C. reinhardtii (biotic origin), however, extracellular and intracellular pro-oxidant processes differed, suggesting that ext racellular H2O2 cannot per se serve as a predictor of cellular oxidative stress or damage.
Abstract: This study sheds light on the short-term dynamics of pro-oxidant processes related to the exposure of C. reinhardtii microalgae to nano-TiO2 using (a) conventional fluorescence probes for cellular pro-oxidant process and (b) a recently developed cytochrome c biosensor for the continuous quantification of extracellular H2O2. The main aims are to investigate nano-TiO2 toxicity and the modifying factors thereof based on the paradigm of oxidative stress and to explore the utility of extracellular H2O2 as a potential biomarker of the observed cellular responses. This is the first study to provide continuous quantitative data on abiotic and biotic nano-TiO2-driven H2O2 generation to systematically investigate the link between extracellular and cellular pro-oxidant responses. Acute exposures of 1 h were performed in two different exposure media (MOPS and lake water), with nominal particle concentrations from 10 mg L−1 to 200 mg L−1, with and without UV pre-illumination. Abiotic and biotic extracellular H2O2 were continuously measured with the biosensor and complemented with endpoints for abiotic ROS (H2DCF-DA), oxidative stress (CellROX® Green) and damage (propidium iodide) measured by flow cytometry at the beginning and end of exposure. Results showed that nano-TiO2 suspensions generated ROS under UV light (abiotic origin) and promoted ROS accumulation in C. reinhardtii (biotic origin). However, extracellular and intracellular pro-oxidant processes differed. Hence, extracellular H2O2 cannot per se serve as a predictor of cellular oxidative stress or damage. The main predictors best describing the cellular responses included “exposure medium”, “exposure time”, “UV treatment” as well as “exposure concentration”.
9 citations
TL;DR: In this article, the orientation of dipolar emitters placed near plasmonic nanostructures has been investigated and shown to have a subtle dependence on the molecular orientation, which is lost when typical calculations assume a random orientation and perform an average over all directions.
Abstract: We computationally explore how the orientation of dipolar emitters placed near plasmonic nanostructures affects their radiative enhancement and spontaneous emission rate. We demonstrate that the expressions for these quantities show a subtle dependence on the molecular orientation, and this information is lost when typical calculations assume a random orientation and perform an average over all directions. This orientation dependence is strongly affected by the location of the emitter, the emission wavelength, and the symmetry of the system. While the plasmonic nanostructure can significantly modify the far-field from a molecule in its vicinity, this modification is heavily dependent on both the wavelength and the orientation of the emitter. We show that if a fluorescent molecule can be constrained to emit in a specific direction, we are able to obtain far superior control over its spontaneous emission and decay rate than otherwise and discuss implications for single molecule experiments.
TL;DR: For the first time, it is shown that by introducing a random medium with appropriate filling factor, absorption in a specific volume can be maximized and this absorption enhancement is broadband and wide-angle and can help design efficient solar cells, light trapping devices, biosensors and random lasers.
Abstract: Efficient optical energy transfer is key to many technologies, ranging from biosensing to photovoltaics. Here, for the first time we show that by introducing a random medium with appropriate filling factor, absorption in a specific volume can be maximized. Using both numerical simulations and an analytical diffusion model, we identify design rules to maximize absorption in the system with different geometrical and scattering properties. By combining a random medium with an open photonic cavity, we numerically demonstrate a 23-fold enhancement of the absorbed energy. We also show how absorption as high as 99% can be reached in a device as thin as 500 μm for normal incidence illumination. Finally, our data indicate that introducing a non-absorbing random medium into a light trapping system for thin solar cells can enhance absorption of energy by a factor of 2.2. This absorption enhancement, caused by the random medium, is broadband and wide-angle and can help design efficient solar cells, light trapping devices, biosensors and random lasers.
TL;DR: In this article, the intrinsic properties of the plasmonic nanostructures studied with the electron energy-loss (EEL) measurements are used to interpret the EELS data.
Abstract: Electron energy-loss spectroscopy (EELS) has become an experimental method of choice for the investigation of localized surface plasmon resonances, allowing the simultaneous mapping of the associated field distributions and their resonant energies with a nanoscale spatial resolution. The experimental observations have been well-supported by numerical models based on the computation of the Lorentz force acting on the impinging electrons by the scattered field. However, in this framework, the influence of the intrinsic properties of the plasmonic nanostructures studied with the electron energy-loss (EEL) measurements is somehow hidden in the global response. To overcome this limitation, we propose to go beyond this standard, and well-established, electron perspective and instead to interpret the EELS data using directly the intrinsic properties of the nanostructures, without regard to the force acting on the electron. The proposed method is particularly well-suited for the description of coupled plasmonic systems, because the role played by each individual nanoparticle in the observed EEL spectrum can be clearly disentangled, enabling a more subtle understanding of the underlying physical processes. As examples, we consider different plasmonic geometries in order to emphasize the benefits of this new conceptual approach for interpreting experimental EELS data. In particular, we use it to describe results from samples made by traditional thin film patterning and by arranging colloidal nanostructures.
TL;DR: In this paper, the opto-mechanical design of the NFIRAOS beam splitters subsystems (NBS) is presented, and surface deformations are fit to Zernike polynomials using SigFit software.
Abstract: The early-light facility adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). The science beam splitter changer mechanism and the visible light beam splitter are subsystems of NFIRAOS. This paper presents the opto-mechanical design of the NFIRAOS beam splitters subsystems (NBS). In addition to the modal and the structural analyses, the beam splitters surface deformations are computed considering the environmental constraints during operation. Surface deformations are fit to Zernike polynomials using SigFit software. Rigid body motion as well as residual RMS and peak-to-valley surface deformations are calculated. Finally, deformed surfaces are exported to Zemax to evaluate the transmitted and reflected wave front error. The simulation results of this integrated opto-mechanical analysis have shown compliance with all optical requirements.
TL;DR: In this article, the authors discuss and compare different methods (namely full-wave computations based on the surface integral equations method, mode analysis, the Miller's rule, and the effective nonlinear susceptibility method) proposed for the evaluation of the second harmonic generation from plasmonic nanoparticles emphasizing their limitations and advantages.
Abstract: During the last decade, important attention has been devoted to the observation of nonlinear optical processes in plasmonic nanosystems, giving rise to a new field of research called nonlinear plasmonics. The cornerstone of nonlinear plasmonics is the use of the large field enhancement associated with the excitation of localized surface plasmon resonances to reach high nonlinear conversion yields. Among all the nonlinear optical processes, second harmonic generation (SHG), the process whereby two photons at the fundamental frequency are converted into one photon at the second harmonic frequency, is undoubtedly the most studied one due to the relative simplicity of its experimental observation. However, the physical origin of SHG from plasmonic nanostructures hides a lot of subtleties, which are mainly related to its particular behavior upon inversion symmetry. In order to catch all the peculiarities of SHG, it is mandatory to develop dedicated numerical methods able to accurately describe all the underlying physical processes and the influence of the initial assumptions needs to be well-characterized. In this presentation, we discuss and compare different methods (namely full-wave computations based on the surface integral equations method, mode analysis, the Miller’s rule, and the effective nonlinear susceptibility method) proposed for the evaluation of the SHG from plasmonic nanoparticles emphasizing their limitations and advantages. In particular, the design of double resonant antennas for efficient nonlinear conversion at the nanoscale is addressed in detail.