Publications
114 results found
Tilmann B, Huq T, Possmayer T, et al., 2023, Comparison of Harmonic Generation from Crystalline and Amorphous Gallium Phosphide Nanofilms, Advanced Optical Materials, Vol: 11
Gallium phosphide (GaP) is a promising material for nanophotonics, given its large refractive index and a transparency over most of the visible spectrum. However, since easy phase-matching is not possible with bulk GaP, a comprehensive study of its nonlinear optical properties for harmonic generation, especially when grown as thin films, is still missing. Here, second harmonic generation is studied from epitaxially grown GaP thin films, demonstrating that the absolute conversion efficiencies are comparable to a bulk wafer over the pump wavelength range from 1060 to 1370 nm. Furthermore, the results are compared to nonlinear simulations, and the second order nonlinear susceptibility is extracted, showing a similar dispersion and magnitude to that of the bulk material. Furthermore, the third order nonlinear susceptibility of amorphous GaP thin films is extracted from third harmonic generation to be more than one order of magnitude larger than that of the crystalline material, and generation of up to the fifth harmonic is reported. The results show the potential of crystalline and amorphous thin films for nonlinear optics with nanoantennas and metasurfaces, particularly in the visible to near infrared part of the spectrum.
Zotev PG, Wang Y, Andres-Penares D, et al., 2023, Van der Waals Materials for Applications in Nanophotonics, Laser and Photonics Reviews, Vol: 17, ISSN: 1863-8880
Numerous optical phenomena and applications have been enabled by nanophotonic structures. Their current fabrication from high refractive index dielectrics, such as silicon (Si) or gallium phosphide (GaP), pose restricting fabrication challenges while metals, relying on plasmons and thus exhibiting high ohmic losses, limit the achievable applications. An emerging class of layered, so-called van der Waals (vdW), crystals is presented as a viable nanophotonics platform in this work. The dielectric response of 11 mechanically exfoliated thin-film (20–200 nm) vdW crystals is extracted, revealing high refractive indices up to n = 5, pronounced birefringence up to Δn = 3, sharp absorption resonances, and a range of transparency windows from ultraviolet to near-infrared. Nanoantennas are subsequently fabricated on silicon dioxide (SiO2) and gold, utilizing the compatibility of vdW thin films with a variety of substrates. Pronounced Mie resonances are observed due to the high refractive index contrast on SiO2, leading to a strong exciton-photon coupling regime as well as largely unexplored high-quality-factor, hybrid Mie-plasmon modes on gold. Additional vdW-material-specific degrees of freedom in fabrication are further demonstrated by realizing nanoantennas from stacked twisted crystalline thin-films, enabling control of nonlinear optical properties, and post-fabrication nanostructure transfer, important for nano-optics with sensitive materials.
Dranczewski J, Fischer A, Tiwari P, et al., 2023, Plasma etching for fabrication of complex nanophotonic lasers from bonded InP semiconductor layers, Micro and Nano Engineering, Vol: 19
Integrating optically active III-V materials on silicon/insulator platforms is one potential path towards improving the energy efficiency and performance of modern computing. Here we demonstrate the applicability of direct wafer bonding combined with plasma etching to the fabrication of complex nanophotonic systems out of InP layers. We explore and optimise the plasma etching of InP, validating existing processes and developing improved ones. We explore the use of microdisk lasing as a way to evaluate fabrication fidelity, and demonstrate that we can create complex lasing systems of interest to us: coupled disk cavities and random network lasers.
Barelli M, Vidal C, Fiorito S, et al., 2023, Single-Photon Emitting Arrays by Capillary Assembly of Colloidal Semiconductor CdSe/CdS/SiO2 Nanocrystals., ACS Photonics, Vol: 10, Pages: 1662-1670, ISSN: 2330-4022
The controlled placement of colloidal semiconductor nanocrystals (NCs) onto planar surfaces is crucial for scalable fabrication of single-photon emitters on-chip, which are critical elements of optical quantum computing, communication, and encryption. The positioning of colloidal semiconductor NCs such as metal chalcogenides or perovskites is still challenging, as it requires a nonaggressive fabrication process to preserve the optical properties of the NCs. In this work, periodic arrays of 2500 nanoholes are patterned by electron beam lithography in a poly(methyl methacrylate) (PMMA) thin film on indium tin oxide/glass substrates. Colloidal core/shell CdSe/CdS NCs, functionalized with a SiO2 capping layer to increase their size and facilitate deposition into 100 nm holes, are trapped with a close to optimal Poisson distribution into the PMMA nanoholes via a capillary assembly method. The resulting arrays of NCs contain hundreds of single-photon emitters each. We believe this work paves the way to an affordable, fast, and practical method for the fabrication of nanodevices, such as single-photon-emitting light-emitting diodes based on colloidal semiconductor NCs.
Tirole R, Vezzoli S, Galiffi E, et al., 2023, Double-slit time diffraction at optical frequencies, NATURE PHYSICS, ISSN: 1745-2473
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Granchi N, Lodde M, Stokkereit K, et al., 2023, Near-field imaging of optical nanocavities in hyperuniform disordered materials, Physical Review B, Vol: 107, ISSN: 2469-9950
Hyperuniform disordered photonic materials have recently been shown to display large, complete photonic band gaps and isotropic optical properties, and are emerging as strong candidates for a plethora of optoelectronic applications, making them competitive with many of their periodic and quasiperiodic counterparts. In this work, high quality factor optical cavities in hyperuniform disordered architectures are fabricated through semiconductor slabs and experimentally addressed by scanning near-field optical microscopy. The wide range of confined cavity modes that we detect arise from carefully designed local modifications of the dielectric structure. Previous works on hyperuniform disordered photonic systems have previously identified several Anderson localized states spectrally located at the PBG edges with relatively high quality factors. In this work, by engineering the structural parameters of the cavity, we achieve an experimental quality factor of order 6000 (higher than the one of the Anderson states) and we demonstrate that three types of localized modes of different nature coexist within a small area and in a relatively narrow spectral window of the disordered correlated system. Their compatibility with general boundary constraints, in contrast with ordered architectures that suffer strict layout constraints imposed by photonic crystals' axes orientation, makes optical cavities in disordered hyperuniform patterns a flexible optical insulator platform for planar optical circuits.
Kalinic B, Cesca T, Balasa IG, et al., 2023, Quasi-BIC Modes in All-Dielectric Slotted Nanoantennas for Enhanced Er3+Emission, ACS PHOTONICS, ISSN: 2330-4022
Sapienza R, Pendry J, Maier S, et al., 2022, Saturable time-varying mirror based on an epsilon-near-zero material, Physical Review Applied, Vol: 18, ISSN: 2331-7019
We report a switchable time-varying mirror, composed of an indium-tin-oxide–gold bilayer, displaying a tenfold modulation of reflectivity (ΔR≈0.6), which saturates for a driving-pump intensity Ipump≈100GW/cm2. Upon interacting with the saturated time-varying mirror, the frequency content of a reflected pulse is extended up to 31 THz, well beyond the pump spectral content (2.8 THz). We interpret the spectral broadening as a progressive shortening of the mirror rise time from 110 fs to below 30 fs with increasing pump power, which is confirmed by four-wave-mixing experiments and partially captured by a linear time-varying model of the mirror. A temporal response unbounded by the pump bandwidth enables applications for spectral manipulation from time-varying systems with impact for communication networks, optical switching, and computing.
Sapienza R, Barahona M, Saxena D, et al., 2022, Sensitivity and spectral control of network lasers, Nature Communications, Vol: 13, Pages: 1-7, ISSN: 2041-1723
Recently, random lasing in complex networks has shown efficient lasing over more than 50 localised modes, promoted by multiple scattering over the underlying graph. If controlled, these network lasers can lead to fast-switching multifunctional light sources with synthesised spectrum. Here, we observe both in experiment and theory high sensitivity of the network laser spectrum to the spatial shape of the pump profile, with some modes for example increasing in intensity by 280% when switching off 7% of the pump beam. We solve the nonlinear equations within the steady state ab-initio laser theory (SALT) approximation over a graph and we show selective lasing of around 90% of the strongest intensity modes, effectively programming the spectrum of the lasing networks. In our experiments with polymer networks, this high sensitivity enables control of the lasing spectrum through non-uniform pump patterns. We propose the underlying complexity of the network modes as the key element behind efficient spectral control opening the way for the development of optical devices with wide impact for on-chip photonics for communication, sensing, and computation.
Sapienza R, 2022, Controlling random lasing action, NATURE PHYSICS, Vol: 18, Pages: 976-979, ISSN: 1745-2473
Trivedi M, Saxena D, Ng WK, et al., 2022, Self-organized lasers from reconfigurable colloidal assemblies, NATURE PHYSICS, Vol: 18, Pages: 939-+, ISSN: 1745-2473
Tavakoli N, Spalding R, Lambertz A, et al., 2022, Over 65% sunlight absorption in a 1 mu m Si slab with hyperuniform texture, ACS Photonics, Vol: 9, Pages: 1206-1217, ISSN: 2330-4022
Thin, flexible, and invisible solar cells will be a ubiquitous technology in the near future. Ultrathin crystalline silicon (c-Si) cells capitalize on the success of bulk silicon cells while being lightweight and mechanically flexible, but suffer from poor absorption and efficiency. Here we present a new family of surface texturing, based on correlated disordered hyperuniform patterns, capable of efficiently coupling the incident spectrum into the silicon slab optical modes. We experimentally demonstrate 66.5% solar light absorption in free-standing 1 μm c-Si layers by hyperuniform nanostructuring for the spectral range of 400 to 1050 nm. The absorption equivalent photocurrent derived from our measurements is 26.3 mA/cm2, which is far above the highest found in literature for Si of similar thickness. Considering state-of-the-art Si PV technologies, we estimate that the enhanced light trapping can result in a cell efficiency above 15%. The light absorption can potentially be increased up to 33.8 mA/cm2 by incorporating a back-reflector and improved antireflection, for which we estimate a photovoltaic efficiency above 21% for 1 μm thick Si cells.
Granchi N, Spalding R, Lodde M, et al., 2022, Near-field investigation of luminescent hyperuniform disordered materials, Advanced Optical Materials, Vol: 10, Pages: 1-9, ISSN: 2195-1071
Disordered photonic nanostructures have attracted tremendous interest in the past three decades, not only due to the fascinating and complex physics of light transport in random media, but also for peculiar functionalities in a wealth of interesting applications. Recently, the interest in dielectric disordered systems has received new inputs by exploiting the role of long-range correlation within scatterer configurations. Hyperuniform photonic materials, that share features of photonic crystals and random systems, constitute the archetype of systems where light transport can be tailored from diffusive transport to a regime dominated by light localization due to the presence of photonic band gap. Here, advantage is taken of the combination of the hyperuniform disordered (HuD) design in slab photonics, the use of embedded quantum dots for feeding the HuD resonances, and near-field hyperspectral imaging with sub-wavelength resolution in the optical range to explore the transition from localization to diffusive transport. It is shown, theoretically and experimentally, that photonic HuD systems support resonances ranging from strongly localized modes to extended modes. It is demonstrated that Anderson-like modes with high Q/V are created, with small footprint, intrinsically reproducible and resilient to fabrication-induced disorder, paving the way for a novel photonic platform for quantum applications.
Tirole R, Vezzoli S, Galiffi E, et al., 2022, Single and double slit time diffraction at optical frequencies
In a temporal version of a single slit and Young's double slit experiments, newly generated optical frequencies form a diffraction pattern. The spectral extent of these frequencies is beyond the expected bandwidth of the modulation.
Molkens K, Tanghe I, Saxena D, et al., 2022, Coupled Micro Ring Lasers based on Hybrid Integration of Colloidal Quantum Dots
Coupled and Random laser require flexible fabrication methods for photonic integration. Series of (random) coupled micro ring resonators were made with colloidal quantum dots and their unique properties investigated in both linear and lasing regimes.
Galiffi E, Tirole R, Yin S, et al., 2022, Photonics of time-varying media, ADVANCED PHOTONICS, Vol: 4
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- Citations: 42
Morozov S, Vezzoli S, Myslovska A, et al., 2021, Purifying single photon emission from a CdSe/CdS colloidal quantum dot, Publisher: ArXiv
Colloidal quantum dots are robust and flexible single photon emitters forroom-temperature applications, but their purity is strongly reduced at highpump powers, due to multiexcitonic emission which cannot be easily filtered dueto the photo-luminescence spectral broadening at room temperature. Giant-shellquantum dots feature a large blueshift of the biexciton spectrum due toelectron-hole wave function engineering and piezoelectric charge separation,which can be exploited for spectral separation of the single exciton from themultiexciton emission. Here, by spectral filtering, we show that we can recoveran excellent single-photon emission, with $g_2{(0)} < 0.05$ (resolutionlimited), even at high pump powers above saturation of the exciton emission.The bright and pure single-photon generation shown here has importantapplications in quantum information technology and random-number generation.
Glass D, Quesada-Cabrera R, Bardey S, et al., 2021, Probing the role of atomic defects in photocatalytic systems through photoinduced enhanced raman scattering, ACS Energy Letters, Vol: 6, Pages: 4273-4281, ISSN: 2380-8195
Even in ultralow quantities, oxygen vacancies (VO) drastically impact keyproperties of metal oxide semiconductors, such as charge transport, surface adsorption,and reactivity, playing central roles in functional materials performance. Currentmethods used to investigate VO often rely on specialized instrumentation under far fromideal reaction conditions. Hence, the influence of VO generated in situ during catalyticprocesses has yet to be probed. In this work, we assess in situ extrinsic surface VOformation and lifetime under photocatalytic conditions which we compare tophotocatalytic performance. We show for the first time that lifetimes of in situ generatedatomic VO play more significant roles in catalysis than their concentration, with strongcorrelations between longer-lived VO and higher photocatalytic activity. Our resultsindicate that enhanced photocatalytic efficiency correlates with goldilocks VOconcentrations, where VO densities must be just right to encourage carrier transportwhile avoiding charge carrier trapping.
Sortino L, Zotev PG, Phillips CL, et al., 2021, Bright single photon emitters with enhanced quantum efficiency in a two-dimensional semiconductor coupled with dielectric nano-antennas, Nature Communications, Vol: 12, ISSN: 2041-1723
Single photon emitters in atomically-thin semiconductors can be deterministically positioned using strain induced by underlying nano-structures. Here, we couple monolayer WSe2 to high-refractive-index gallium phosphide dielectric nano-antennas providing both optical enhancement and monolayer deformation. For single photon emitters formed on such nano-antennas, we find very low (femto-Joule) saturation pulse energies and up to 104 times brighter photoluminescence than in WSe2 placed on low-refractive-index SiO2 pillars. We show that the key to these observations is the increase on average by a factor of 5 of the quantum efficiency of the emitters coupled to the nano-antennas. This further allows us to gain new insights into their photoluminescence dynamics, revealing the roles of the dark exciton reservoir and Auger processes. We also find that the coherence time of such emitters is limited by intrinsic dephasing processes. Our work establishes dielectric nano-antennas as a platform for high-efficiency quantum light generation in monolayer semiconductors.
Dagdeviren OE, Glass D, Sapienza R, et al., 2021, The effect of photoinduced surface oxygen vacancies on the charge carrier dynamics in TiO2 films, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 8348-8354, ISSN: 1530-6984
Metal-oxide semiconductors (MOS) are widely utilized for catalytic and photocatalytic applications in which the dynamics of charged carriers (e.g., electrons, holes) play important roles. Under operation conditions, photoinduced surface oxygen vacancies (PI-SOV) can greatly impact the dynamics of charge carriers. However, current knowledge regarding the effect of PI-SOV on the dynamics of hole migration in MOS films, such as titanium dioxide, is solely based upon volume-averaged measurements and/or vacuum conditions. This limits the basic understanding of hole-vacancy interactions, as they are not capable of revealing time-resolved variations during operation. Here, we measured the effect of PI-SOV on the dynamics of hole migration using time-resolved atomic force microscopy. Our findings demonstrate that the time constant associated with hole migration is strongly affected by PI-SOV, in a reversible manner. These results will nucleate an insightful understanding of the physics of hole dynamics and thus enable emerging technologies, facilitated by engineering hole-vacancy interactions.
Ta VD, Caixeiro S, Saxena D, et al., 2021, Biocompatible Polymer and Protein Microspheres with Inverse Photonic Glass Structure for Random Micro‐Biolasers, Advanced Photonics Research, Vol: 2, ISSN: 2699-9293
Ta VD, Caixeiro S, Saxena D, et al., 2021, Biocompatible polymer and protein microspheres with inverse photonic glass structure for random micro‐biolasers, Advanced Photonics Research, Vol: 2, Pages: 1-7, ISSN: 2699-9293
The miniaturization of random lasers to the micrometer scale is challenging but fundamental for the integration of lasers with photonic integrated circuits and biological tissues. Herein, it is demonstrated that random lasers with a diameter from 30 to 160 μm can be achieved by using a simple emulsion process and selective chemical etching. These tiny random laser sources are made of either dye-doped polyvinyl alcohol (PVA) or bovine serum albumin (BSA) and they are in the form of microporous spheres with monodisperse pores of 1.28 μm in diameter. Clear lasing action is observed when the microporous spheres are optically excited with powers larger than the lasing threshold, which is 154 μJ mm−2 for a 75 μm diameter PVA microporous sphere. The lasing wavelength redshifts 10 nm when the PVA microsphere diameter increases from 34 to 160 μm. For BSA microspheres, the lasing threshold is around 55 μJ mm−2 for a 70 μm diameter sphere and 104 μJ mm−2 for a 35 μm diameter sphere. The simple fabrication process reported allows for detail studies of morphology and size, important for fundamental studies of light–matter interaction in complex media, and applications in photonic integrated circuits, photonic barcoding, and optical biosensing.
Tirole R, Attavar T, Dranczewski J, et al., 2021, Time Diffraction in an Epsilon-Near-Zero Metasurface
We observe strong, efficient all-optical modulations and frequency-shift due to time diffraction in a thin film of ITO over gold. Excitation of the Berreman mode leads to redshift and spectral broadening from a nonlinear grating.
Sortino L, Zotev PG, Sapienza R, et al., 2021, Enhanced light-matter interaction in atomically thin semiconductors and 2D single photon emitters coupled to dielectric nano-antennas
Tirole R, Attavar T, Dranczewski J, et al., 2021, Time Diffraction in an Epsilon-Near-Zero Metasurface, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Sortino L, Zotev PG, Sapienza R, et al., 2021, Enhanced light-matter interaction in atomically thin semiconductors and 2D single photon emitters coupled to dielectric nano-antennas, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Lee JB, Walker H, Li Y, et al., 2020, Template dissolution interfacial patterning of single colloids for nanoelectrochemistry and nanosensing, ACS Nano, Vol: 14, Pages: 17693-17703, ISSN: 1936-0851
Deterministic positioning and assembly of colloidal nanoparticles (NPs) onto substrates is a core requirement and a promising alternative to top-down lithography to create functional nanostructures and nanodevices with intriguing optical, electrical, and catalytic features. Capillary-assisted particle assembly (CAPA) has emerged as an attractive technique to this end, as it allows controlled and selective assembly of a wide variety of NPs onto predefined topographical templates using capillary forces. One critical issue with CAPA, however, lies in its final printing step, where high printing yields are possible only with the use of an adhesive polymer film. To address this problem, we have developed a template dissolution interfacial patterning (TDIP) technique to assemble and print single colloidal AuNP arrays onto various dielectric and conductive substrates in the absence of any adhesion layer, with printing yields higher than 98%. The TDIP approach grants direct access to the interface between the AuNP and the target surface, enabling the use of colloidal AuNPs as building blocks for practical applications. The versatile applicability of TDIP is demonstrated by the creation of direct electrical junctions for electro- and photoelectrochemistry and nanoparticle-on-mirror geometries for single-particle molecular sensing.
Rubino A, Huq T, Dranczewski J, et al., 2020, Efficient third harmonic generation from FAPbBr(3) perovskite nanocrystals, Journal of Materials Chemistry C, Vol: 8, Pages: 15990-15995, ISSN: 2050-7526
The development of versatile nanostructured materials with enhanced nonlinear optical properties is relevant for integrated and energy efficient photonics. In this work, we report third harmonic generation from organic lead halide perovskite nanocrystals, and more specifically from formamidinium lead bromide nanocrystals, ncFAPbBr3, dispersed in an optically transparent silica film. Efficient third order conversion is attained for excitation in a wide spectral range in the near infrared (1425 nm to 1650 nm). The maximum absolute value of the modulus of the third order nonlinear susceptibility of ncFAPbBr3, χ(3)NC, is derived from modelling both the linear and nonlinear behaviour of the film and is found to be χ(3)NC = 1.46 × 10−19 m2 V−2 (or 1.04 × 10−11 esu) at 1560 nm excitation wavelength, which is of the same order as the highest previously reported for purely inorganic lead halide perovskite nanocrystals (3.78 × 10−11 esu for ncCsPbBr3). Comparison with the experimentally determined optical constants demonstrates that maximum nonlinear conversion is attained at the excitonic resonance of the perovskite nanocrystals where the electron density of states is largest. The ease of synthesis, the robustness and the stability provided by the matrix make this material platform attractive for integrated nonlinear devices.
Persano L, Szukalski A, Gaio M, et al., 2020, Dye stabilization and wavelength tunability in lasing fibers based on DNA, Advanced Optical Materials, Vol: 8, ISSN: 2195-1071
Lasers based on biological materials are attracting an increasing interest in view of their use in integrated and transient photonics. Deoxyribonucleic acid (DNA) as optical biopolymer in combination with highly emissive dyes has been reported to have excellent potential in this respect. However, achieving miniaturized lasing systems based on solid-state DNA shaped in different geometries to confine and enhance emission is still a challenge, and the physicochemical mechanisms originating fluorescence enhancement are not fully understood. Herein, a class of wavelength-tunable lasers based on DNA nanofibers is demonstrated, for which optical properties are highly controlled through the system morphology. A synergistic effect is highlighted at the basis of lasing action. Through a quantum chemical investigation, it is shown that the interaction of DNA with the encapsulated dye leads to hindered twisting and suppressed channels for the nonradiative decay. This is combined with effective waveguiding, optical gain, and tailored mode confinement to promote morphologically controlled lasing in DNA-based nanofibers. The results establish design rules for the development of bright and tunable nanolasers and optical networks based on DNA nanostructures.
Sapienza R, Morozov S, Vezzoli S, et al., 2020, Electrical control of single-photon emission in highly-charged individual colloidal quantum dots, Science Advances, Vol: 6, ISSN: 2375-2548
Electron transfer to an individual quantum dot promotes the formation of charged excitons with enhanced recombination pathways and reduced lifetimes. Excitons with only one or two extra charges have been observed and exploited for very efficient lasing or single–quantum dot light-emitting diodes. Here, by room-temperature time-resolved experiments on individual giant-shell CdSe/CdS quantum dots, we show the electrochemical formation of highly charged excitons containing more than 12 electrons and 1 hole. We report the control over intensity blinking, along with a deterministic manipulation of quantum dot photodynamics, with an observed 210-fold increase in the decay rate, accompanied by 12-fold decrease in the emission intensity, while preserving single-photon emission characteristics. These results pave the way for deterministic control over the charge state, and room-temperature decay rate engineering for colloidal quantum dot–based classical and quantum communication technologies.
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