We proposed a cost-effective and compact optical setup for laser Interference lithography. The system is based on the special designed wave-front splitting prisms with only one spatial filter for two and tree coplanar beams interference.
This configuration allows to reduce the total size of the setup. Employing a low coherence laser diode source allows to reduce the price and the size of the setup as well. The coherence length of the source was improved by Littrow type external cavity configuration. The patterning on large area (1 cm2) with sub-micron resolution was successfully demonstrated.
The aim of this study was to develop mid-infrared chalcogenide sensor and perform its functionalization by polymers in order to detect various hydrocarbon pollutants in water and to ensure an efficient attenuation of the water absorption bands. Selenide waveguides were fabricated by radiofrequency magnetron sputtering on silicon substrates using two different glass target compositions, for cladding and guiding layers. A hydrophobic polymer was deposited on the surface of zinc selenide prisms to allow its characterization by ATR-FTIR (Attenuated Total Reflectance-Fourier Transform InfraRed) spectroscopy. Benzene, toluene and ortho-, meta- and para-xylenes in solutions of distilled water at concentrations ranging from 10 ppb to 20 ppm were simultaneously detected and the measured limit of detection was determined to be equal to 250 ppb. However, the limit of detection must be improved to meet environmental standards. To achieve this goal, metallic nanostructures were deposited on the surface of the chalcogenide waveguides to increase the sensitivity of the future optical sensor thanks to the plasmon resonance phenomena. Thus, the fabrication of a heterostructure composed of gold nanoparticles deposited by electron beam evaporation was performed on a slab selenide waveguide in order to assess SEIRA (Surface-Enhanced InfraRed Absorption) effect.
ZnO is a multifunctional nanomaterial having various applications. The real challenge is to produce large scale, well-aligned, reproducible ZnO nanowires (NWs) using low-cost techniques. The aim of this work is to show a simple approach for the uniform growth of NWs, on entire silicon wafers, using a low-temperature chemical method. A study of the substrate size dependent growth of NWs was conducted to understand the limitations in the growth. A time dependent growth study was performed on ZnO NWs grown on 3-inch wafers to track their morphological evolution. Simultaneous growth of ZnO NWs on two 4-inch wafers will be demonstrated.
We present the design and the numerical modeling of electrically-tunable plasmonic metasurface absorber based on the Babinet’s principle in the mid-infrared spectrum. The plasmonic metasurface consist of an array of gold nanoantennas on a dielectric layer followed by gold substrate in a metal-insulator-metal (MIM) configuration. A graphene layer placed on top of the array enables electrical tuning of the antenna optical response. Finite-difference time-domain (FDTD) -based simulations were carried out using a commercially implemented FDTD Solutions to obtain the optical response of the metasurface. Based on the Babinet’s principle, we design and numerically modeled the complementary metasurface. We found that, even with the graphene layer, the complementary metasurfaces comply with the Babinet’s principle. These metasurfaces can found application as electrically-tunable sources in the mid-infrared range.
Quantum technologies are seen to be within reach for ripe applications with recent developments in quantum optics and photonics resulting into better control of quantum systems [1]. Many platforms, such as photonic crystals and cavities involving complex fabrications as well as many materials such as diamond or III-V semiconductors have been proposed for quantum photonics. We will report on a different material approach and in particular with the use of ZnO as a promising quantum photonics materials. Several aspects will be covered where we will show some results on using ZnO as a photonics material for guiding light and have a strong light-matter interaction with other quantum emitters. We will also show how ZnO nanowires (NWs) can be used as photodetectors and as such being integrated on optical circuits. Finally, we will develop why ZnO is interesting intrinsically for quantum technologies and in particular by manipulating and using defects within its band gap.
The detection of high energy radiation relies frequently on its conversion to visible or near-ultraviolet light by means of scintillator crystals. As the generated visible light then needs to be detected outside the crystal, it is of paramount importance to model the complete system involving the scintillator, the conversion process and the final detection outside the crystal. In this work we present a general modeling scheme of such detection process. Taking into account the bulk scintillator crystal shape and the precise geometry of the scintillator output interface (at micron or nanometric scale), we evaluate the performance of the system in terms of the number of photons and their spatial distribution on the detector. This numerical tool can be used, for example, to assess the performance of image reconstruction techniques used for Positron Emission Tomography (PET) scanners. The influence of nanostructures placed on top of the output interface on the overall response is analyzed and compared to that of a plane exit surface. Our results indicate that the electromagnetic response of the scintillator output interface plays a crucial role in the final detection.
The optical properties of ZnO has been widely investigated in detail. Typical photoluminescence (PL) of ZnO contains two parts of emission: near bandgap transition induced ultraviolet emission, and a relatively wide visible emission ranging from green to red, which is closely related to concentration of the structural defects. While the green luminescent has been reported to be associated with oxygen vacancies Vo. In this work, we report on an efficient technique namely desulfurization to increase the amount of oxygen vacancy in a ZnO nanowires array. In the case of the desulfurized sample the PL is increased by more than 1 order of magnitude as to compare with the sulfurized one and more than 2 orders of magnitude as to compare with the as grown sample. Structural analysis as well as morphological analysis confirm the origin of the green band emission enhancement in PL emission. Samples preparation as well an in-depth analysis including quantum efficiency will be presented and discussed within the frame of new rare-earth free phosphor material.
Among alternative nanomaterials for energy related photonic applications, one-dimensional semiconductor nanowires are of a great interest due to their physical properties coming from electronic or quantum confinement. In particular, ZnO nanowires (or nanorods) has been widely investigated since ZnO has many unique properties such as wide direct band gap, large exciton binding energy and relatively high refractive index. Large optical gain also makes ZnO a well suited material for energy transfer in hybrid systems and especially optical energy transfer. There are however two issues remaining to be addressed, one is related to the control in size and dispersion in nanowires array and the other is related to the modeling of nanowires arrays. In this study, we report on a theoretical study on ZnO nanowires, in order to reach a better understanding of the mechanisms that govern the light propagation in nanowires arrays.
A phenomenological model has been developed and discussed. The model is able to describe the experimentally measured light transmission nanowires arrays. A slab of nanospheres and rough layers with thickness waviness were combined to simplify the nanowires structure description. This phenomenological description was proved to be feasible by fitting the experimental data. As a conclusion, light transmitted by randomly distributed nanowires can be explained by the combination of Mie theory and a rough Fresnel reflection at the interfaces.
Two-dimensional transition metal dichalcogenides (TMDs), which are atomically thin semiconductors consisting of transition metals M-(Mo, W, Sn, etc.) covalently bonded to chalcogens X-(S, Se, Te), have recently been the focus of extensive research activity due to their remarkable properties and especially emission properties. Nevertheless, such remarkable properties can strongly be altered once the atomically thin layer is deposited on a support.
In this study, we report on the integration of freestanding TMDs. Monolayer (1-L) MoS2, WS2, and WSe2 as representative TMDs are transferred on ZnO nanorods (NRs), used here as nanostructured substrates. The photoluminescence (PL) spectra of 1-L TMDs on NRs show a giant PL intensity enhancement, compared with those of 1-L TMDs on SiO2. The strong increases in Raman and PL intensities, along with the characteristic peak shifts, confirm the absence of stress in the TMDs on NRs. In depth analysis of the PL emission also reveals that the ratio between the exciton and trion peak intensity is almost not modified after transfer. The latter shows that the effect of charge transfer between the 1-L TMDs and ZnO NRs is here negligible. Furthermore, confocal PL and Raman spectroscopy reveal a fairly consistent distribution of PL and Raman intensities. These observations are in agreement with a very limited points contact between the support and the 1-L TMDs. The entire process reported here is scalable and may pave the way for the development of very efficient ultrathin optoelectronics.
ZnO is a promising II-VI semiconductor for UV applications although p-type ZnO is not yet available. Nevertheless it remains an alternative material for GaN and its alloy InGaN. For example, the exciton binding energy of ZnO (60 meV) is higher than that of GaN (21 meV). This allows ZnO to emit light at ambient temperature and interestingly, it increases the device brightness. Besides promising intrinsic properties, light-matter control and especially in the UV relies on the ability of material nanostructuring. We present here two different kinds of top-down process in order to nanostructure ZnO. The first one relies on Electron Beam Lithography (EBL) combined with a lift-off process and inductively coupled plasma (ICP) reactive ion etching (RIE). Nickel (Ni) has been used as a mask in order to have a high selectivity in the presence of C2F6 and O2 ionized gases. The etching rate used was 26nm/s in order to avoid roughness. The second process is called Direct Holographic Patterning (DHP). ZnO thin films have been holographicaly patterned for the first time by direct photodissolution in NaCl solution using laser interference lithography. Application of an electrical potential strongly increases the dissolution rate and decreases the pattern formation time. Both processes will be discussed in terms of their respective potential for light confinement in the UV.
Luminescent nanoscale materials (LNMs) have received widespread interest in sensing and lighting applications due to their enhanced emissive properties. For sensing applications, LNMs offer improved sensitivity and fast response time which allow for lower limits of detection. Meanwhile, for lighting applications, LNMs, such as quantum dots, offer an improved internal quantum efficiency and controlled color rendering which allow for better lighting performances. Nevertheless, due to their nanometric dimensions, nanoscale materials suffer from extremely weak luminescence excitation (i.e. optical absorption) limiting their luminescence intensity, which in turn results in a downgrade in the limits of detection and external quantum efficiencies. Therefore, enhancing the luminescence excitation is a major issue for sensing and lighting applications.
In this work, we report on a novel photonic approach to increase the luminescence excitation of nanoscale materials. Efficient luminescence excitation increase is achieved via a gain-assisted waveguided energy transfer (G-WET). The G-WET concept consists on placing nanoscale materials atop of a waveguiding active (i.e. luminescent) layer with optical gain. Efficient energy transfer is thus achieved by exciting the nanoscale material via the tail of the waveguided mode of the active layer emission. The G-WET concept is demonstrated on both a nanothin layer of fluorescent sensitive polymer and on CdSe/ZnS quantum dots coated on ZnO thin film, experimentally proving up to an 8-fold increase in the fluorescence of the polymer and a 3-fold increase in the luminescence of the CdSe/ZnS depending of the active layer emission regime (stimulated vs spontaneous emission). Furthermore, we will discuss on the extended G-WET concept which consists on coating nanoscale materials on a nanostructured active layer. The nanostructured active layer offers the necessary photonic modulation and a high specific surface which can presumably lead to a more efficient G-WET concept. Finally, the efficiency as well as the observation conditions of the GWET will be discussed and compared with more conventional charge transfer or dipole-dipole energy transfer.
Due to its wide direct band gap and large exciton binding energy allowing for efficient excitonic emission at room
temperature, ZnO has attracted attention as a luminescent material in various applications such as UV-light emitting
diodes, chemical sensors and solar cells. While low-cost growth techniques, such as chemical bath deposition
(CBD), of ZnO thin films and nanostructures have been already reported; nevertheless, ZnO thin films and
nanostructures grown by costly techniques, such as metalorganic vapour phase epitaxy, still present the most
interesting properties in terms of crystallinity and internal quantum efficiency.
In this work, we report on highly efficient and highly crystalline ZnO micropods grown by CBD at a low
temperature (< 90°C). XRD and low-temperature photoluminescence (PL) investigations on as-grown ZnO
micropods revealed a highly crystalline ZnO structure and a strong UV excitonic emission with internal quantum
efficiency (IQE) of 10% at room temperature. Thermal annealing at 900°C of the as-grown ZnO micropods leads to
further enhancement in their structural and optical properties. Low-temperature PL measurements on annealed ZnO
micropods showed the presence of phonon replicas, which was not the case for as-grown samples. The appearance
of phonon replicas provides a strong proof of the improved crystal quality of annealed ZnO micropods. Most
importantly, low-temperature PL reveals an improved IQE of 15% in the excitonic emission of ZnO micropods. The
ZnO micropods IQE reported here are comparable to IQEs reported on ZnO structures obtained by costly and more
complex growth techniques. These results are of great interest demonstrating that high quality ZnO microstructures
can be obtained at low temperatures using a low-cost CBD growth technique.
KEYWORDS: Nanostructures, Waveguides, Radio propagation, Geometrical optics, Near field optics, Silicon, Near field scanning optical microscopy, Surface plasmons, Wave propagation, Nanowires
The study of surface plasmon-polaritons interactions in metallic nanostructures has been a topic of interest during last years due to their use in various areas such as the photonics, chemistry and biology. Example of use is found in biosensors for the efficient detection of biological analyte and in nanophotonic elements for on-chip photonics.
Here, we study the interactions properties of localized surface plasmons in a hybrid waveguiding structure made of bi-dimensional array of gold nanowires vertically integrated on silicon-on-insulator waveguides across the near infrared spectrum. With the use of near-field scanning optical microscopy (NSOM) in perturbation mode, we qualitatively obtained the spectral response of such hybrid structure through intensity near field maps of the light propagation. These experimental results demonstrate that metallic nanostructures integrated on silicon are suitable for the development of localized surface plasmon integrated devices or metallic metamaterials.
We discuss here different strategies for making arrays of Au nanoparticles using copolymer templates. Top-down and
bottom-up routes are considered and the optical properties of as-prepared Au nanoparticles are discussed and compared
to numerical simulations. Potential for applications such as biosensors or strain sensors is also assessed.
KEYWORDS: Waveguides, Metamaterials, Near field scanning optical microscopy, Silicon, Near field optics, Dielectric polarization, Light wave propagation, Dielectrics, Interfaces
We address the experimental validation of the technological feasibility and operation of the metamaterials in a guided wave configuration in the spectral domain around 1.5μm. For our experiments we considered a 2D array of 200×50×50nm gold cut wires placed on the top of a 10μm wide and 200nm thick silicon waveguide. The transmission spectral measurements performed in the spectral range between 1.25 and 1.64μm using an end-fire coupling setup, revealed a marked dip for TE polarized light, corresponding to the cut wires resonance frequency obtained by numerical modeling. No such a dip in transmission was observed for TM polarized light, i.e. when the electric filed is perpendicular to the layers interface and the orientation of the cut wires. The scanning near field optical microscopy experiments (SNOM), performed in the same spectral range, revealed for TE polarized light a strong enhancement of the electric field confined in the region between the ends of the adjacent cut wires. These results confirm the efficient excitation of the cut wires resonance in a guided wave configuration for the TE polarization. The ability for local engineering of the field interaction with the metamaterial layer and thus the control in such a way of the light flow in a guiding slab, paves the way to a novel class of photonic devices.
In this work, we demonstrate successful interfacing between metallic nanoparticle (MNP) chain supporting localized
surface plasmons (LSP) and silicon-on-insulator (SOI) waveguides. We show that the optical energy carried by a TE SOI
waveguide mode at telecom wavelengths can be efficiently transferred into MNP chains deposited on the waveguide top,
whatever the number of metallic particles (from 5 to 50). Especially in short chains, most of the energy can be
transferred into the fourth or fifth MNP of the chains. Predictions from theoretical models are fully corroborated by
transmission and near-field measurements.
KEYWORDS: Waveguides, Near field optics, Plasmonics, Silicon, Near field scanning optical microscopy, Copper, Near field, Wave propagation, Light wave propagation, Atomic force microscopy
Plasmonic waveguiding structures have the ability to confine and propagate light over short distances, typically
less than a hundred micrometers. This short propagation length is the price that is paid for confining light to
dimensions on the order of a hundred of nanometers. With these scales in mind, several plasmonic devices can be
proposed (e.g. wavelength multiplexors) and some of them have been already demonstrated such as Y junctions
and directional couplers. Although the dimensions involved in such structures are below the diffraction limit,
large-scale optical characterization techniques, such as transmitted power, are still employed. In this contribution,
we present a characterization technique for the study of the guided modes in plasmonic gap waveguiding structures
that resolves subwavelength-scale features, as it is based on atomic force microscope and on near field scattering
optical microscope in guided detection.
KEYWORDS: Waveguides, Near field scanning optical microscopy, Near field optics, Brain-machine interfaces, Near field, Wave propagation, Silicon, Multimode interference devices, Silicon photonics, Light wave propagation
Optical devices based on SOI have been fabricated and tested for the last decade by using far field optics.
Alternatively, near-field scanning optical microscopes (NSOM) have the ability to reach unique optical resolution
by converting the evanescent waves into radiation waves that can be detected by conventional far field optics.
Thus, the aim of this paper is to show the most recent capabilities of the NSOM in a guided detection to probe
SOI-based structures. By using this simple yet powerful configuration, we can observe the propagation of the
light in Si-based devices and thus measure the propagation characteristics of the guided modes.
We study both experimentally and numerically far-field radiation patterns of single metallic nanowires coupled
to weak confined optical waveguides. The radiation pattern resulting from the interaction of the nanowire and
the optical mode depends strongly on the mode properties (polarization and wavenumber) and on the antenna
properties (material and size). To investigate these phenomena we compare the electric far-field distributions
computed with different numerical methods (Green's tensor technique, rigourous coupled wave method, Fourier
modal method). We also compare simulated results to experimental measurements obtained over a large spectral
domain ranging from 400 nm to 1000 nm. This study should be useful for optimizing nanostructured photonic
circuits elements.
We developed a home-made sample-holder unit used for 2D nano-positioning with millimeter travelling ranges. For each
displacement axis, the system includes a long range travelling stage and a piezoelectric actuator for accurate positioning.
Specific electronics is integrated according to metrological considerations, enhancing the repeatability performances.
The aim of this work is to demonstrate that near-field microscopy at the scale of a chip is possible. We chose here to
characterize highly integrated optical structures. For this purpose, the sample-holder is integrated into an Atomic Force
Microscope in order to perform optical imaging. To demonstrate the overall performances, a millimeter scale optical
images have been realized.
KEYWORDS: Near field optics, Near field scanning optical microscopy, Waveguides, Heterodyning, Atomic force microscopy, Brain-machine interfaces, Silicon, Integrated optics, Dispersion, Wave propagation
This article presents recent advances in scattering-type near field optical scanning microscopy used as a powerful
characterization tool for integrated optics. By significant examples, it is shown that this specific probe microscopy based
on an Atomic Force Microscope setup with optical heterodyne detection functionalities allows for in situ quantitative
study of the complex field propagating in compact silicon on insulator photonic structures (single channel waveguides,
MMI splitters and microdisk resonators).
This paper deals with a new spectrograph on integrated optics. It is composed of an Y-junction where the two
junction arms are guided in a loop structure in order to obtain an interference pattern. The measurement of this
intensity distribution gives access to the optical spectrum source after a Inverse Fourier Transform. To measure
it, we use the property of the loop composed of a bent waveguide which is a leaky structure. Depending on
the radius of the bent waveguide, a part of the light leaks from the waveguide to outside. The radiated power,
proportional to the intensity in the waveguide, is coupled into a plan waveguide set near the bent waveguide.
Indeed the two structures are separated by a gap which changes along the periphery of the loop. This structure
enables both to control the leaking light part and to confine in the plan waveguide the propagation of the radiated
field. Thereby, the radiated intensity is measured at a peculiar distance of the loop on a perpendicular plan to the
input waveguide. So, the interference pattern measured is magnified by the ratio of the plan waveguide length
over the loop radius, allowing to use a commercial photodetectors array to sufficiently sample the interference
pattern. The spectrum is finally obtained operating a Discrete Fourier Transform. The device modelization is
divided in two parts. The first part describes the coupling between the bent and the plan waveguide modelised by
a modal method based on a Fourier series expansion (RCWA) combined with an exponential conformal mapping
in order to simulate the electromagnetic field near the loop. The second part describes the Helmholtz-Kirchhoff
theorem to simulate the far-electromagnetic field. From the interference pattern modelized, the spectrum of the
signal is then calculated. A demonstrator in integrated optics on glass is being developed.
In this work, a new micro-extensometric technique to study the local heterogeneities of strain fields in metallic alloys is introduced. It is based on the optical full-field measurement method called the grid method adapted to the micrometric scale. In the first part of the paper, the making of a periodic grating at the surface of the sample by direct interferometric photolithography is explained. The optimization of the grids in terms of phase noise is then addressed.
Local surface plasmons resonances are widely accepted to be the basis for improving the efficiency of absorption and emission processes through a local electromagnetic field enhancement. Nonlinear processes in gold surfaces such as second harmonic generation or two-photon induced photoluminescence are particularly sensitive to this local effect due to their quadratic dependence on the intensity. Isolated regions of enhanced photoluminescence yield on rough gold surfaces were identified emphasizing the physical similarities with surface enhanced Raman scattering (SERS) substrates. In this vein, we investigated luminescence from individual gold nanorods and found that their emission characteristics closely resemble surface plasmon behavior. In particular, we observed spectral similarities between the scattering spectra of individual nanorods and their photoluminescence emission. We also measured a blue-shift of the photoluminescence peak wavelength with decreasing aspect ratio of the nanorods as well as an optically tuneable shape-dependent spectrum of the photoluminescence. The emission yield of single nanorods strongly depends on the orientation of the incident polarization consistent with the properties of surface plasmons.
In the context of optical interconnection applications, we report on results obtained on strained InGaAs quantum well Vertical Cavity Surface Emitting Lasers (VCSELs). Our devices are top p-type DBR oxide-confined VCSEL, grown by metalorganic vapour-phase epitaxy (MOVPE). These lasers exhibit low threshold currents and deliver up to 1.77 mW in continuous wave operation at room temperature. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm at room temperature is reached for a 4 μm oxide diameter VCSEL. The particular design of the active layer based on a large detuning between the gain maximum and the cavity resonance gives our devices a very specific thermal and modal behaviour. Therefore, we study the spectral and spatial distributions of the transverse modes by near field scanning optical microscopy using a micropolymer tip at the end of an optical fibre.
KEYWORDS: Actuators, Near field, Interferometers, Control systems, Mirrors, Heterodyning, Near field optics, Phase shifts, Electronic circuits, Optoelectronics
We report on a new high accuracy home-made sample holder for near field characterization of millimeter long wave guiding structures (Y junction, Multi Modes Interference coupler). The principle of near field characterization is based on an atomic force microscopy tip that is brought to the surface of the sample (in the near field zone) in order to coupled out a small amount of the light confined inside the wave guiding structures. Due to the size of the components, scans as long as a few millimeters are required to get an entire optical mapping of the structure [1]. With the commonly available equipments such a scan is performed by acquiring step by step more than 100 images for a 2 mm scan. The overlapping of the different images is time consuming and unsatisfactory unless a numerical stitching procedure based on topographical details is used. Effective refractive indexes are typically determined with a precision of 10-3 which could be further improved by increasing the millimeter scan resolution. The reason why successive images do not overlap is mainly due to the mechanical system supporting the sample. Actually, the nonlinearity of the actuator and the thermal expansion of the mechanical part prevent us to reach nanometric scale of repeatability on the positioning for micrometric range of displacements. In order to enable long range scans with nanometric repeatability and accuracy, we develop a specific mechanical system controlled by a heterodyne interferometric apparatus and a home-made high frequency electronic board [2]. The position of the sample is measured in real time with a resolution of 0.3 nm. The servo-loop allows to control the position of the sample with a repeatability of 1 nm (1σ) for a displacement of 1 mm. Furthermore our method is insensitive to the nonlinearity of the actuator.
We present a method for mapping the electromagnetic field distribution in the vicinity of noble metal nanoparticles able to sustain localised surface plasmon resonance (LSPR). The field distribution is coded by topographic change in a self-developing photosensitive polymer (PMMA-DR1). Metallic nanostructures are fabricated by e-beam lithography and optically characterised by extinction spectroscopy. Photoinduced topographic changes are checked by means of atomic force microscopy (AFM). The dipolar character of the surface modification around the particles agrees qualitatively with theoretical predictions and a strong correlation between LSPR position and the relief depth is found.
We describe a new method for doping high-quality porous silicon microcavities with erbium using ion implantation, where the erbium is confined to the spacer layer of the structure. This method involves fabricating porous silicon microcavities from a crystalline silicon wafer that has been implanted with erbium to a depth that coincides with a spacer layer of the microcavity. Using this technique erbium doped microcavities with Q-factors in excess of 1500 have been demonstrated. From low temperature photoluminescence measurements we observe a strong modification of the spontaneous emission spectrum of the erbium doped PSi, where the emission is enhanced 25 times at the resonance and suppressed elsewhere. Temperature dependent photoluminescence exhibited strong thermal quenching and excitation power dependent photoluminescence measurement showed saturation at high excitation powers. Both of these trends are characteristically similar to luminescent erbium centres in crystalline silicon. In addition we discuss the merits of localising the erbium in the crystalline part of the PSi and its potential for reducing the effects of Auger recombination and energy back-transfer, which limit the performance of the structures at room high temperatures.
We review a number of optical devices made from microporous silicon. Particular emphasis is placed on the fabrication method of porous silicon laser-mirrors, optical microcavities and one-dimensional photonic crystals with true photonic bandgap.
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