We 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.
This Letter describes strong coupling of densely packed molecular emitters in metal−organic frameworks (MOFs) and plasmonic nanoparticle (NP) lattices. Porphyrin-derived ligands with small transition dipole moments in an ordered MOF film were grown on Ag NP arrays. Angle-resolved optical measurements of the MOF-NP lattice system showed the formation of a polariton that is lower in energy and does not cross the uncoupled MOF Q 1 band. Modeling predicted the upper polariton energy and a calculated Rabi splitting of 110 meV. The coupling strength was systematically controlled by detuning the plasmon energy by changing the refractive index of the solvents infiltrating the MOF pores. Through transient absorption spectroscopy, we found that the lower polariton decays quickly at shorter time scales (<500 ps) and slowly at longer times because of energy transfer from the upper polariton. This hybrid system demonstrates how MOFs can function as an accessible excitonic material for polariton chemistry.
We report on the manipulation of magnetization by femtosecond laser pulses in a periodic array of cylindrical nickel nanoparticles. By performing experiments at different wavelength, 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.Plasmonic nanostructures enable strong local enhancements of the optical field in areas that are substantially smaller than the wavelength of incident light. This capability offers prospects for magnetic recording. In heat-assisted magnetic recording (HAMR), a plasmonic near-field transducer (NFT) reduces the switching field of high-anisotropy materials via local heating. 1-3 The NFT in this application is a noble metal nanostructure that is placed near the recording medium. Excitation of the NFT at the plasmon resonance frequency efficiently transfers optical energy to a nanoscale region, enabling local switching at reduced magnetic field. In the realm of ultrafast all-optical switching (AOS), 4,5 the use of noble metal plasmonic antennas has also been considered. By placing gold antennas on top of a ferrimagnetic TbFeCo film, Liu and co-workers demonstrated the confinement of magnetic switching to sub-100 nm length scales. 6 .Independent from HAMR and AOS, a new discipline combining plasmonics and magnetism has emerged recently. 7,8 Experiments on pure ferromagnetic metals demonstrate that, despite stronger ohmic damping, they also support surface plasmon resonances. [9][10][11] This raises the question if one could nanostructure the magnetic medium itself to trigger magnetic switching via local enhancements of the optical field. To study the effect of plasmon resonances on magnetic switching it is advantageous to consider ferromagnetic nanoparticles of uniform size and shape. In such nanoparticles, plasmon resonances determine the magneto-optical activity via the excitation of two orthogonal electric dipoles. 12 Plasmon resonances in single ferromagnetic nanoparticles are rather broad. Yet, ordering of the particles into a periodic array significantly narrows the spectral response. 13 In this geometry, hybridization between localized surface plasmons and the diffracted orders of the array produces intense surface lattice resonances (SLRs). SLR modes a) sebastiaan.van.dijken@aalto.fi and, thereby, the optical, magneto-optical, and magnetic circular dichroism (MCD) properties of a ferromagnetic nanoparticle array can be tuned by changing the period or symmetry of the lattice 13-15 or the shape of the nanoparticles. 16 These versatile designer tools could thus be exploited to spectrally gauge the significance of the inverse Faraday effect and MCD on all-optical switching in ferromagnetic materials, a topic of intense sc...
Organic 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.
Titanium nitride (TiN) is an advantageous plasmonic material for optoelectronic applications that require resilience to extreme irradiation or temperatures. Although TiN is optically similar to noble metals at near-infrared wavelengths under steadystate excitation conditions, their photoexcited properties are distinct at ultrafast time scales. This paper describes the differences in optical properties between coupled TiN nanoparticles in 2D arrays that support surface lattice resonances (SLRs) and TiN nanoparticle arrays that support only localized surface plasmons (LSPs). Compared to symmetric photoinduced peak broadening in the LSPs, we found that SLRs show asymmetric broadening at ps-time scales in transient absorption measurements. Furthermore, TiN nanoparticle arrays were robust and withstood pump fluences exceeding 50 mJ/cm 2 for over half an hour with little to no change in bleach wavelength.
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