Browsing by Author "Hakala, Tommi K."
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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 Hybrid plasmonic lattices with tunable magneto-optical activity(2016-02-22) Kataja, Mikko; Pourjamal, Sara; Maccaferri, Nicolò; Vavassori, Paolo; Hakala, Tommi K.; Huttunen, Mikko J.; Törmä, Päivi; Van Dijken, Sebastiaan; Department of Applied Physics; CIC nanoGUNE; Ikerbasque - Basque Foundation for ScienceWe report on the optical and magneto-optical response of hybrid plasmonic lattices that consist of pure nickel and gold nanoparticles in a checkerboard arrangement. Diffractive far-field coupling between the individual emitters of the lattices results in the excitation of two orthogonal surface lattice resonance modes. Local analyses of the radiation fields indicate that both the nickel and gold nanoparticles contribute to these collective resonances and, thereby, to the magneto-optical activity of the hybrid arrays. The strong effect of noble metal nanoparticles on the magneto-optical response of hybrid lattices opens up new avenues for the realization of sensitive and tunable magneto-plasmonic nanostructures.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 Lasing in Ni Nanodisk Arrays(AMERICAN CHEMICAL SOCIETY, 2019-05-28) Pourjamal, Sara; Hakala, Tommi K.; Nečada, Marek; Freire-Fernández, Francisco; Kataja, Mikko; Rekola, Heikki; Martikainen, Jani Petri; Törmä, Päivi; Van Dijken, Sebastiaan; Department of Applied Physics; Nanomagnetism and Spintronics; Quantum DynamicsWe report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.Item Lasing in small-sized aluminum nanoparticle arrays(SPIE, 2017) Rekola, Heikki T.; Hakala, Tommi K.; Törmä, Païvi; Department of Applied Physics; Engheta, Nader; Noginov, Mikhail A.; Zheludev, Nikolay I.; Quantum DynamicsWe study lasing in regular arrays made from aluminum nanoparticles. We show that these structures function as laser sources at visible wavelengths, even when scaled to an order of magnitude smaller areas compared to existing literature. The aluminum nanoparticles provide a robust platform for studying lasing in plasmonic systems, even when the optical losses are higher compared to silver or gold.Item Multimode Lasing in Supercell Plasmonic Nanoparticle Arrays(American Chemical Society, 2023-11-15) Heilmann, Rebecca; Arjas, Kristian; Hakala, Tommi K.; Törmä, Päivi; Department of Applied Physics; Quantum Dynamics; University of Eastern FinlandMulticolor light sources can be used in applications such as lighting and multiplexing signals. In photonic and plasmonic systems, one way to achieve multicolor light is via multimode lasing. To achieve this, plasmonic nanoparticle arrays are typically arranged in superlattices that lead to multiple dispersions of the single arrays coupled via the Bragg superlattice Bragg modes. Here, we show an alternative way to enable multimode lasing in plasmonic nanoparticle arrays. We design a supercell in a square lattice by leaving part of the lattice sites empty. This results in multiple dispersive branches caused by the supercell period and hence creates additional band edges that can support lasing. We experimentally demonstrate multimode lasing in such a supercell array. Furthermore, we identify the lasing modes by calculating the dispersion by combining the structure factor of the array design with an empty lattice approximation. We conclude that the lasing modes are the 74th Γ- and 106th X-point of the supercell. By tuning the square lattice period with respect to the gain emission, we can control the modes that lase. Finally, we show that the lasing modes exhibit a combination of transverse electric and transverse magnetic mode characteristics in polarization-resolved measurements.Item One-Dimensional Plasmonic Nanoparticle Chain Lasers(ACS Publications, 2018-05-16) Rekola, Heikki T.; Hakala, Tommi K.; Törmä, Päivi; Quantum Dynamics; Department of Applied PhysicsControlling and generating coherent light fields in the nanoscale is critical for reducing the size of photonic circuitry. There are several demonstrations of zero-, one-, two-, and three-dimensional nanolaser architectures. Here we experimentally demonstrate a one-dimensional plasmonic laser, which consists of a periodic chain of aluminum nanoparticles and organic gain media. Lasing is observed at visible wavelengths, with clear thresholds and line widths down to 0.11 nm. Lasing occurs in a dark mode that extends over the whole structure, even outside the pumped area. The single lithography step fabrication and one-dimensional character allow for easy integration of these laser sources with other plasmonic structures.Item Optical characterization of DNA origami-shaped silver nanoparticles created through biotemplated lithography(Royal Society of Chemistry, 2022-07-14) Kabusure, Kabusure M.; Piskunen, Petteri; Yang, Jiaqi; Kataja, Mikko; Chacha, Mwita; Ojasalo, Sofia; Shen, Boxuan; Hakala, Tommi K.; Linko, Veikko; Department of Bioproducts and Biosystems; Biohybrid Materials; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; University of Eastern Finland; Department of Bioproducts and BiosystemsHere, we study optically resonant substrates fabricated using the previously reported BLIN (biotemplated lithography of inorganic nanostructures) technique with single triangle and bowtie DNA origami as templates. We present the first optical characterization of BLIN-fabricated origami-shaped silver nanoparticle patterns on glass surfaces, comprising optical transmission measurements and surface-enhanced Raman spectroscopy. The formed nanoparticle patterns are examined by optical transmission measurements and used for surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Polarization-resolved simulations reveal that the higher SERS enhancement observed for the bowties is primarily due to spectral overlap of the optical resonances with the Raman transitions of R6G. The results manifest the applicability of the BLIN method and substantiate its potential in parallel and high-throughput substrate manufacturing with engineered optical properties. While the results demonstrate the crucial role of the formed nanogaps for SERS, the DNA origami may enable even more complex nanopatterns for various optical applications.Item Plasmon-induced demagnetization and magnetic switching in nickel nanoparticle arrays(2018-02-12) Kataja, Mikko; Freire-Fernández, Francisco; Witteveen, Jorn P.; Hakala, Tommi K.; Törmä, Päivi; Van Dijken, Sebastiaan; Department of Applied Physics; Nanomagnetism and Spintronics; Quantum DynamicsWe report on the manipulation of magnetization by femtosecond laser pulses in a periodic array of cylindrical nickel nanoparticles. By performing experiments at different wavelengths, we show that the excitation of collective surface plasmon resonances triggers demagnetization in zero field or magnetic switching in a small perpendicular field. Both magnetic effects are explained by plasmon-induced heating of the nickel nanoparticles to their Curie temperature. Model calculations confirm the strong correlation between the excitation of surface plasmon modes and laser-induced changes in magnetization.Item Polarization dependent beaming properties of a plasmonic lattice laser(IOP Publishing Ltd., 2021-06) Asamoah, Benjamin O.; Partanen, Henri; Mohamed, Sughra; Heikkinen, Janne; Halder, Atri; Koivurova, Matias; Nečada, Marek; Set, Tero; Turunen, Jari; Friberg, Ari T.; Hakala, Tommi K.; Department of Applied Physics; Quantum Dynamics; University of Eastern Finland; Tampere UniversityWe study beaming properties of laser light produced by a plasmonic lattice overlaid with organic fluorescent molecules. The crossover from spontaneous emission regime to stimulated emission regime is observed in response to increasing pump fluence. This transition is accompanied by a strong reduction of beam divergence and emission linewidth due to increased degree of spatial and temporal coherence, respectively. The feedback for the lasing signal is shown to be mainly one-dimensional due to the dipolar nature of the surface lattice resonance. Consequently, the beaming properties along x and y directions are drastically different. From the measurements, we obtain the M 2 value along both principal directions of the square lattice as a function of the pump fluence. Our work provides the first detailed analysis of the beam quality in plasmonic lattice lasers and reveals the underlying physical origin of the observed strong polarization dependent asymmetry of the lasing signal.Item Quasi-BIC mode lasing in a quadrumer plasmonic lattice(ACS Publications, 2022-01-19) Heilmann, Rebecca; Salerno, Grazia; Cuerda, Javier; Hakala, Tommi K.; Törmä, Päivi; Department of Applied Physics; Quantum Dynamics; University of Eastern FinlandPlasmonic lattices of metal nanoparticles have emerged as an effective platform for strong light–matter coupling, lasing, and Bose–Einstein condensation. However, the full potential of complex unit cell structures has not been exploited. On the other hand, bound states in continuum (BICs) have attracted attention, as they provide topologically protected optical modes with diverging quality factors. Here, we show that quadrumer nanoparticle lattices enable lasing in a quasi-BIC mode with a highly out-of-plane character. By combining theory with polarization-resolved measurements of the emission, we show that the lasing mode has a topological charge. Our analysis reveals that the mode is primarily polarized out-of-plane as a result of the quadrumer structure. The quality factors of the out-of-plane BIC modes of the quadrumer array can be exceedingly high. Our results unveil the power of complex multiparticle unit cells in creating topologically protected high-Q modes in periodic nanostructures.Item Raman enhancement in bowtie-shaped aperture-particle hybrid nanostructures fabricated with DNA-assisted lithography(Royal Society of Chemistry, 2023-05-21) Kabusure, Kabusure M.; Piskunen, Petteri; Yang, Jiaqi; Linko, Veikko; Hakala, Tommi K.; Department of Bioproducts and Biosystems; Biohybrid Materials; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; University of Eastern FinlandWe report on efficient surface-enhanced Raman spectroscopy (SERS) supporting substrates, which are based on deoxyribonucleic acid (DNA)-assisted lithography (DALI) and a layered configuration of materials. In detail, we used nanoscopic DNA origami bowtie templates to form hybrid nanostructures consisting of aligned silver bowtie-shaped particles and apertures of similar shape in a silver film. We hypothesized that this particular geometry could facilitate a four-fold advantage in Raman enhancement compared to common particle-based SERS substrates, and further, we verified these hypotheses experimentally and by finite difference time domain simulations. In summary, our DALI-fabricated hybrid structures suppress the background emission, allow emission predominantly from the areas of high field enhancement, and support additional resonances associated with the nanoscopic apertures. Finally, these nanoapertures also enhance the fields associated with the resonances of the underlying bowtie particles. The versatility and parallel nature of our DNA origami-based nanofabrication scheme and all of the above-mentioned features of the hybrid structures therefore make our optically resonant substrates attractive for various SERS-based applications.Item Scattering dominated spatial coherence and phase correlation properties in plasmonic lattice lasers(IOP Publishing Ltd., 2022-12-01) Heikkinen, Janne I.; Asamoah, Benjamin; Calpe, Roman; Nečada, Marek; Koivurova, Matias; Hakala, Tommi K.; Institute of Photonics; Quantum Dynamics; Tampere University; Department of Applied PhysicsWe present a comprehensive study of the polarization and spatial coherence properties of the lasing modes supported by a four-fold symmetric plasmonic lattice. We can distinguish the scattering induced effects from the lattice geometry induced effects by modifying only the diameter of the particles while keeping the lattice geometry constant. Customized interferometric measurements reveal that the lasing emission undergoes a drastic change from 1D to 2D spatial coherence with increasing particle size, accompanied with dramatic changes in the far field polarization and beaming properties. By utilizing T-matrix scattering simulations, we reveal the physical mechanism governing this transition. In particular, we find that there exists increased radiative coupling in the diagonal directions at the plane of the lattice when the particle diameter is increased. Finally, we demonstrate that the x- and y-polarized (degenerate) lasing modes become phase locked with sufficiently large particles.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 Ultrafast Pulse Generation in an Organic Nanoparticle-Array Laser(2018-04-11) Daskalakis, Konstantinos S.; Väkeväinen, Aaro I.; Martikainen, Jani Petri; Hakala, Tommi K.; Törmä, Päivi; Department of Applied Physics; Quantum DynamicsNanoscale coherent light sources offer potentially ultrafast modulation speeds, which could be utilized for novel sensors and optical switches. Plasmonic periodic structures combined with organic gain materials have emerged as promising candidates for such nanolasers. Their plasmonic component provides high intensity and ultrafast nanoscale-confined electric fields, while organic gain materials offer fabrication flexibility and a low acquisition cost. Despite reports on lasing in plasmonic arrays, lasing dynamics in these structures have not been experimentally studied yet. Here we demonstrate, for the first time, an organic dye nanoparticle-array laser with more than a 100 GHz modulation bandwidth. We show that the lasing modulation speed can be tuned by the array parameters. Accelerated dynamics is observed for plasmonic lasing modes at the blue side of the dye emission.
