Browsing by Author "Moilanen, Antti J."
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Item Bose–Einstein condensation in a plasmonic lattice(2018-07) Hakala, Tommi K.; Moilanen, Antti J.; Väkeväinen, Aaro I.; Guo, Rui; Martikainen, Jani Petri; Daskalakis, Konstantinos S.; Rekola, Heikki T.; Julku, Aleksi; Törmä, Päivi; Department of Applied Physics; Quantum DynamicsBose–Einstein condensation is a remarkable manifestation of quantum statistics and macroscopic quantum coherence. Superconductivity and superfluidity have their origin in Bose–Einstein condensation. Ultracold quantum gases have provided condensates close to the original ideas of Bose and Einstein, while condensation of polaritons and magnons has introduced novel concepts of non-equilibrium condensation. Here, we demonstrate a Bose–Einstein condensate of surface plasmon polaritons in lattice modes of a metal nanoparticle array. Interaction of the nanoscale-confined surface plasmons with a room-temperature bath of dye molecules enables thermalization and condensation in picoseconds. The ultrafast thermalization and condensation dynamics are revealed by an experiment that exploits thermalization under propagation and the open-cavity character of the system. A crossover from a Bose–Einstein condensate to usual lasing is realized by tailoring the band structure. This new condensate of surface plasmon lattice excitations has promise for future technologies due to its ultrafast, room-temperature and on-chip nature.Item Bose–Einstein condensation in plasmonic lattices(Aalto University, 2021) Moilanen, Antti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Quantum Dynamics; Perustieteiden korkeakoulu; School of Science; Törmä, Päivi, Prof., Aalto University, Department of Applied Physics, FinlandPlasmonics is the study of the interaction between light and metallic structures at the nanoscale. This dissertation explores metallic nanostructures which enable coupling photons to the electrons in the metal, thereby confining light in space smaller than the wavelength. This allows for observing macroscopic quantum-coherent phenomena at room temperature, such as the first Bose-Einstein condensate made of light and electrons observed in this dissertation. The research focuses on periodic arrays (lattices) of gold nanoparticles that are overlaid with organic fluorescent molecules. The molecules can be excited optically by an external laser. The molecules emit photons into the lattice, exciting optical resonances supported by the array structure. When the concentration of molecules is sufficiently high, the lattice resonances can be strongly coupled with the molecules, which modifies the energy states of both. At strong coupling, the lattice resonances and the molecules form new type of quasiparticles with properties of both light and matter. The dissertation consists of five research articles. In Publication I, we introduce the first Bose-Einstein condesate in a plasmonic system. The condensate is formed at room temperature in a picosecond timescale. In Publication II, we achieve the first plasmonic Bose-Einstein condensate at the strong coupling regime. The strongly coupled condensate is 100000 times more luminous than the first plasmonic condensate. Due to the room temperature operation and high luminosity, the strongly coupled plasmonic condensate provides a promising platform for fundamental studies of condensates of light and also for possible applications, for example, in the fields of sensing and optical communications. In Publication III, we study spatial and temporal coherence of the strongly coupled plasmonic Bose-Einstein condensate in large arrays. The condensate studied in this work is half a millimeter long, making it reportedly the largest luminous condensate to date. In Publication IV, we report our observations on the phase and polarization properties of the strongly coupled plasmonic Bose-Einstein condensate. We observe a non-trivial phase distribution, which allows for creating different polarization textures. In Publication V, we present a new theoretical model for strongly coupled organic systems. With the new model we compute, for instance, lasing phase diagrams both at the weak and the strong coupling regime and pinpoint the origin of effective interactions in strongly coupled organic systems.Item Converting an organic light-emitting diode from blue to white with bragg modes(ACS Publications, 2019-10-08) Daskalakis, Konstantinos S.; Freire-Fernández, Francisco; Moilanen, Antti J.; Van Dijken, Sebastiaan; Törmä, Päivi; Department of Applied Physics; Quantum Dynamics; Nanomagnetism and SpintronicsOrganic light-emitting diodes (OLEDs) have been established as versatile light sources that allow for easy integration in large-area surfaces and flexible substrates. In addition, the low fabrication cost of OLEDs renders them particularly attractive as general lighting sources. Current methods for the fabrication of white-light OLEDs rely on the combination of multiple organic emitters and/or the incorporation of multiple cavity modes in a thick active medium. These architectures introduce formidable challenges in both device design and performance improvements, namely, the decrease of efficiency with increasing brightness (efficiency roll-off) and short operational lifetime. Here we demonstrate, for the first time, white-light generation in an OLED consisting of a sub-100 nm thick blue single-emissive layer coupled to the photonic Bragg modes of a dielectric distributed Bragg reflector (DBR). We show that the Bragg modes, although primarily located inside the DBR stack, can significantly overlap with the emissive layer, thus efficiently enhancing emission and outcoupling of photons at selected wavelengths across the entire visible light spectrum. Moreover, we show that color temperature can be tuned by the DBR parameters, offering great versatility in the optimization of white-light emission spectra.Item Lasing and condensation in plasmonic lattices(SPIE, 2019) Hakala, Tommi K.; Rekola, Heikki T.; Väkeväinen, Aaro I.; Martikainen, Jani P.; Nečada, Marek; Moilanen, Antti J.; Törmä, Päivi; Department of Applied Physics; Subramania, Ganapathi S.; Foteinopoulou, Stavroula; Quantum DynamicsI review our recent findings on lasing / condensation in plasmonic nanoparticle lattices1-5. The system properties can be tailored with high precision, including the lasing / condensation energies, linewidths, as well as the dimensionality of the feedback. For a 2-dimensional (2-D) square lattice, we identify lasing in the bright and the dark mode of the system1. By reducing the dimensionality to 1-D we observe the dark mode lasing2. In broken symmetry 2-dimensional rectangular lattices, we observe multimode lasing3. In honeycomb lattices with hexagonal symmetry, we observe 6 beams with specific off-normal angles and polarization properties corresponding to six-fold symmetry of such a lattice4. Finally, I review our recent studies in plasmonic Bose-Einstein condensation in plasmonic lattices5.Item Mode switching dynamics in organic polariton lasing(American Physical Society, 2022-11-15) Moilanen, Antti J.; Arnardóttir, Kristín B.; Keeling, Jonathan; Törmä, Päivi; Department of Applied Physics; Quantum Dynamics; Technical University of Denmark; University of St AndrewsWe study the dynamics of multimode polariton lasing in organic microcavities by using a second-order cumulant equation approach. By inspecting the time evolution of the photon mode occupations, we show that if multiple lasing peaks are observed in time-integrated mode occupations, the reason can be either bimodal lasing or temporal switching between several modes. The former takes place within a narrow range of parameters while the latter occurs more widely. We find that the origin of the temporal switching is different in the weak- and strong-coupling regimes. At weak coupling the different gradients of mode occupation vs pump power is the determining factor, while for strong coupling it is changes in the eigenmodes and gain spectrum upon pumping. This difference is revealed by investigating the photoluminescence and momentum-resolved gain spectra. Our results underscore the importance of understanding the time evolution of the populations when characterizing the lasing behavior of a multimode polariton system, and show how these features differ between weak and strong coupling.Item Multimode Organic Polariton Lasing(American Physical Society, 2020-12-02) Arnardottir, Kristin B.; Moilanen, Antti J.; Strashko, Artem; Törmä, Päivi; Keeling, Jonathan; Department of Applied Physics; Quantum Dynamics; University of St Andrews; Flatiron InstituteWe present a beyond-mean-field approach to predict the nature of organic polariton lasing, accounting for all relevant photon modes in a planar microcavity. Starting from a microscopic picture, we show how lasing can switch between polaritonic states resonant with the maximal gain, and those at the bottom of the polariton dispersion. We show how the population of nonlasing modes can be found, and by using two-time correlations, we show how the photoluminescence spectrum (of both lasing and nonlasing modes) evolves with pumping and coupling strength, confirming recent experimental work on the origin of blueshift for polariton lasing.Item Polarization and Phase Textures in Lattice Plasmon Condensates(AMERICAN CHEMICAL SOCIETY, 2021-06-23) Taskinen, Jani M.; Kliuiev, Pavel; Moilanen, Antti J.; Törmä, Päivi; Department of Applied PhysicsPolarization textures of light may reflect fundamental phenomena, such as topological defects, and can be utilized in engineering light beams. They have been observed, for instance, in photonic crystal lasers and semiconductor polariton condensates. Here we demonstrate domain wall polarization textures in a plasmonic lattice Bose-Einstein condensate. A key ingredient of the textures is found to be a condensate phase that varies spatially in a nontrivial manner. The phase of the Bose-Einstein condensate is reconstructed from the real- and Fourier-space images using a phase retrieval algorithm. We introduce a simple theoretical model that captures the results and can be used for design of the polarization patterns and demonstrate that the textures can be optically switched. The results open new prospects for fundamental studies of non-equilibrium condensation and sources of polarization-structured beams.Item Spatial and Temporal Coherence in Strongly Coupled Plasmonic Bose-Einstein Condensates(American Physical Society, 2021-12-15) Moilanen, Antti J.; Daskalakis, Konstantinos S.; Taskinen, Jani M.; Törmä, Päivi; Department of Applied Physics; Quantum DynamicsWe report first-order spatial and temporal correlations in strongly coupled plasmonic Bose-Einstein condensates. The condensate is large, more than 20 times the spatial coherence length of the polaritons in the uncondensed system and 100 times the healing length, making plasmonic lattices an attractive platform for studying long-range spatial correlations in two dimensions. We find that both spatial and temporal coherence display nonexponential decay; the results suggest power-law or stretched exponential behavior with different exponents for spatial and temporal correlation decays.Item Sub-picosecond thermalization dynamics in condensation of strongly coupled lattice plasmons(Nature Publishing Group, 2020-12-01) Väkeväinen, Aaro I.; Moilanen, Antti J.; Nečada, Marek; Hakala, Tommi K.; Daskalakis, Konstantinos S.; Törmä, Päivi; Department of Applied Physics; Quantum DynamicsBosonic condensates offer exciting prospects for studies of non-equilibrium quantum dynamics. Understanding the dynamics is particularly challenging in the sub-picosecond timescales typical for room temperature luminous driven-dissipative condensates. Here we combine a lattice of plasmonic nanoparticles with dye molecule solution at the strong coupling regime, and pump the molecules optically. The emitted light reveals three distinct regimes: one-dimensional lasing, incomplete stimulated thermalization, and two-dimensional multimode condensation. The condensate is achieved by matching the thermalization rate with the lattice size and occurs only for pump pulse durations below a critical value. Our results give access to control and monitoring of thermalization processes and condensate formation at sub-picosecond timescale. Understanding the sub-picosecond dynamics of driven-dissipative condensates of interacting bosons is challenging. Here the authors combine a lattice of plasmonic nanoparticles with a dye molecule solution in strong coupling and reveal distinct lasing, stimulated thermalization, and condensation regimes.Item Temporal mode switching during polariton condensation(Nature Publishing Group, 2024-12) Urbonas, Darius; Moilanen, Antti J.; Arnardottir, Kristin B.; Scherf, Ullrich; Mahrt, Rainer F.; Törmä, Päivi; Stöferle, Thilo; Department of Applied Physics; Quantum Dynamics; IBM Zurich Research Laboratory; Technical University of Denmark; University of WuppertalMultimode behavior plays a key role in a wide range of nonlinear optical phenomena. Multiple exciton-polariton modes can attain macroscopic population as observed in time-integrated measurements. Recent theory work has shown that, rather than being simultaneously in many modes, the population may temporally switch between the modes. However, the origin and the dynamics of multimode condensation has not been experimentally addressed. Here, we study the dynamics of exciton-polariton condensation into multiple modes of Gaussian defect microcavities filled with ladder type polymer gain material methyl-substituted ladder-type poly(p-phenylene) MeLPPP. We deploy a second-order cumulant model to simulate the dynamics of the system and find picosecond-timescale switching between condensate modes. By interferometric measurements we reveal the experimental signatures of such mode competition behaviour.