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We introduce nonlinear microscopy with phase-engineered incident beams. By controlling the phase across an incident Hermite-Gaussian HG10 beam, we vary the longitudinal electric field component at focus, allowing tailoring of second-harmonic generation from vertically-oriented nanowires.
The optical properties of metal nanoparticles are mostly due to localized surface plasmon resonances. Such resonances can be strongly modified by interparticle coupling when the particles are arranged in regular arrays. We investigate the role of lattice effects in the second-harmonic generation from arrays of metal nanoparticles.
We investigate second-harmonic generation from arrays of metal nanoparticles as a function of the incident angle of light into the structure. The generated signal is significantly affected by the surface-lattice resonances of the structure.
We discuss various mechanisms that are important in optimizing the second-order nonlinear optical response of metamaterials based on arrays of plasmonic metal nanoparticles. The response is enhanced by high quality particle resonances as well as interparticle coupling through the lattice. In addition, geometrical effects may play an unexpected role, superseding straightforward resonant effects.
Chirality is one of the most fundamental and essential structural properties of biological molecules. Many important biological molecules including amino acids and polysaccharides are intrinsically chiral. Conventionally, chiral species can be distinguished by interaction with circularly polarized light, and circular dichroism is one of the best‐known approaches for chirality detection. As a linear...
Using the ultrafast excitation, surface enhancement effect on the dynamics of vibrational modes coupled to the electronic transition of the lowest excited state of MEH-PPV has been studied in MEH-PPV-functionalized nanoantennas for the first time.
Since the discovery of carbon nanotubes (CNT), tremendous efforts have been done to control and characterize their properties [1]. To this date, however, the nonlinear optical properties of CNTs remain underexploited. Although second-harmonic generation (SHG), third-harmonic generation (THG), and four-wave mixing (FWM) techniques have been used earlier, such studies used CNT films, bulk CNT samples,...
Development of non-invasive and sensitive characterization tools for lipids is essential e.g. for atherosclerosis research. Although third-harmonic generation (THG) microscopy has been shown to be capable of imaging lipid structures [1], polarization-sensitivity in this imaging mode remains unexplored. Furthermore, the use of unconventional polarizations, e.g., radial polarization (RP), in label-free...
Organic materials are expected to provide an inexpensive and easily processable alternative to inorganic crystals, which are currently used as high-performance nonlinear optical (NLO) materials [1]. In addition to strong and ultrafast NLO response, some organic molecules possess an advantage that the response can be switched “on” and “off by external means. However, turning the molecular level changes...
Optical antennas convert propagating far-field radiation into localized near-fields [1]. Perhaps the simplest optical antenna is a sharp metal tip, which is commonly utilized in near-field microscopy and spectroscopy [1,2]. Usually, the coupling of far-field light to the near-field requires either a field polarized along the tip axis (longitudinal field) [2] or a surface grating on the tip [3]. Here,...
Second-harmonic generation from arrays of gold nanoparticles exhibits interference between electric-dipole and higher multipole (magnetic-dipole and electric-quadrupoles) effects. We show that improved sample quality suppresses the role of higher multipole effects in second-harmonic generation from L-shaped gold nanoparticles, thereby opening the possibility of reaching the pure dipole limit. This...
Plasmon resonances of metal nanoparticles can lead to strong local electromagnetic fields near the particles and thus enhance their optical response. Nanoscale variations in the local fields can also enable magnetic dipoles and electric quadrupoles to contribute to the optical responses [1]. Very small nanoscale features, such as defects, can also support their own plasmonic modes and thereby modify...
We demonstrate a resonant waveguide structure that enhances second-harmonic generation by a factor of at least 5500 compared to a flat reference surface in the same geometry. We further show that the structure diffracts second-harmonic radiation in four different directions.
We use two-beam second-harmonic generation to separate the surface (electric-dipole) and bulk (magnetic-dipole and electric-quadrupole)-type contributions to the second-order nonlinear optical response of gold films of different thicknesses. Surprisingly, the bulk-type response is more sensitive to surface morphology than the surface-type response.
We propose new second-harmonic-generation probes of surface chirality, based on circular polarizations or handed superpositions of radial and azimuthal polarizations. Because of normal incidence focusing, the techniques are not sensitive to anisotropy.
We use two-beam second-harmonic generation to separate the surface and bulk contributions to the second-order nonlinearity of gold. The results provide direct evidence of bulk contributions, nevertheless, surface-like contributions dominate the measured signals.
We present evidence of local-field and multipole effects in second-harmonic generation from optical metamaterials consisting of arrays of metal nanoparticles and nanodimers with a nanogap. Second-harmonic generation from T-shaped nanodimers is not driven primarily by strong gap fields, instead symmetry of the local fundamental field distribution in the structure plays a key role. Interference between...
We present a centimeter-scale array of gold nanocones realized by nanoimprint lithography and e-beam evaporation. Field concentration at the tip of the cones is shown to enhance second-harmonic generation from the array significantly.
T-shaped gold nanodimers with nanogaps are chiral when their horizontal and vertical bars have non-orthogonal orientations. The resulting optical activity in second-harmonic generation exhibits unexpected gap dependence, which is explained by local-field effects.
We prepare diffractive arrays of metal nanoparticles that possess molecular and structural chirality. Both cases lead to comparative chiral polarization effects, which must be interpreted as arising from chirality of the experimental setup.
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