Solar Transparent Radiators by Optical Nanoantennas

Architectural windows are a major cause of thermal discomfort as the inner glazing during cold days can be several degrees colder than the indoor air. Mitigating this, the indoor temperature has to be increased, leading to unavoidable thermal losses. Here we present solar thermal surfaces based on complex nanoplasmonic antennas that can raise the temperature of window glazing by up to 8 K upon solar irradiation while transmitting light with a color rendering index of 98.76. The nanoantennas are directional, can be tuned to absorb in different spectral ranges, and possess a structural integrity that is not substrate-dependent, and thus they open up for application on a broad range of surfaces.status: publishe

Laser manipulation of plasmonic nanoparticles for SERS and sensing

Optical tweezers have found widespread use in studies of biological macromolecules and in manipulation of microscopic objects, including biological cells and a variety of dielectric particles. But rapid progress over the last decade has demonstrated that optical tweezers also can be used as a powerful method for manipulation and control of plasmonic metal nanostructures. Here, we review our recent results in this area with a focus on the interaction between nanoparticles confined in an optical trap and applications in surface-enhanced Raman scattering spectroscopy

Optical tweezers for Raman spectroscopy

The integration of laser tweezers with Raman spectroscopy for optical manipulation and spectroscopic analysis of individual micro- and nanoscopic objects in physics, chemistry, and the life sciences

Optical manipulation of plasmonic nanoparticles using laser tweezers

Plasmonic nanoparticles, typically gold and silver colloids, can be trapped by a highly focused Gaussian beam. The behavior of the particles in an optical trap, such as the alignment, stability and interaction between particles, depends on their plasmonic nature, determined by the correlation between the size, shape and material of the particles, and the wavelength and polarization of the trapping laser. For instance, an elongated nanoparticle aligns parallel to the polarization of a NIR trapping laser to minimize the optical potential energy. However, nanowires tend to align perpendicular to the polarization. A dimer of two isotropic nanoparticles in principle acts similar to a nanorod with its "long axis" (dimer axis) parallel to the laser polarization. These results are evidenced by dark-field scattering imaging and spectra, and agree well with discrete dipole approximation simulations of the near-fields around different nanostructures. Elongated nanoparticles, dimers and nanowires all rotate when the laser polarization is rotated. Irradiated under a circularly polarized laser, trapped objects spin spontaneously due to the transfer of angular momentum from the incident photons. The interaction between two gold nanoparticles in a dimer is complex because it involves the optical potential and the DLVO potential. The latter can be probed to some extent using dark-field scattering spectroscopy. \ua9 2010 SPIE

Optical manipulation of plasmonic nanoparticles using laser tweezers

Plasmonic nanoparticles, typically gold and silver colloids, can be trapped by a highly focused Gaussian beam. The behavior of the particles in an optical trap, such as the alignment, stability and interaction between particles, depends on their plasmonic nature, determined by the correlation between the size, shape and material of the particles, and the wavelength and polarization of the trapping laser. For instance, an elongated nanoparticle aligns parallel to the polarization of a NIR trapping laser to minimize the optical potential energy. However, nanowires tend to align perpendicular to the polarization. A dimer of two isotropic nanoparticles in principle acts similar to a nanorod with its "long axis" (dimer axis) parallel to the laser polarization. These results are evidenced by dark-field scattering imaging and spectra, and agree well with discrete dipole approximation simulations of the near-fields around different nanostructures. Elongated nanoparticles, dimers and nanowires all rotate when the laser polarization is rotated. Irradiated under a circularly polarized laser, trapped objects spin spontaneously due to the transfer of angular momentum from the incident photons. The interaction between two gold nanoparticles in a dimer is complex because it involves the optical potential and the DLVO potential. The latter can be probed to some extent using dark-field scattering spectroscopy. \ua9 2010 SPIE

Alignment, Rotation, and Spinning of Single Plasmonic Nanoparticles and Nanowires Using Polarization Dependent Optical Forces

We demonstrate optical alignment and rotation of individual plasmonic nanostructures with lengths from Lens of nanometers to several micrometers using a single beam of linearly polarized near-infrared laser light. Silver nanorods and dimers of gold nanoparticles align parallel to the laser polarization because of the high long-axis dipole polarizability. Silver nanowires, in contrast, spontaneously turn perpendicular to the incident polarization and predominantly attach at the wire ends, in agreement with electrodynamics simulations. Wires, rods, and dimers all rotate if the incident polarization is turned. In the case of nanowires, we demonstrate spinning at an angular frequency of similar to 1 Hz due to transfer of spin angular momentum from circularly polarized light

Nanogaps for SERS applications

The nanogap is possibly the single most important physical entity in surface-enhanced Raman scattering. Nanogaps between noble metal nanostructures deliver extremely high electric field-enhancement, resulting in an extraordinary amplification of both the excitation rate and the emission rate of Raman active molecules situated in the gap. In some cases, the resulting surface-enhancement in the gap can be so high that Raman spectra from single molecules can be measured. Here, we briefly review some important concepts and experimental results on nanoscale gaps for SERS applications

Recent Advances in Plasmonic Sensors

Plasmonic sensing has been an important multidisciplinary research field and has been extensively used in detection of trace molecules in chemistry and biology. The sensing techniques are typically based on surface-enhanced spectroscopies and surface plasmon resonances (SPRs). This review article deals with some recent advances in surface-enhanced Raman scattering (SERS) sensors and SPR sensors using either localized surface plasmon resonances (LSPRs) or propagating surface plasmon polaritons (SPPs). The advances discussed herein present some improvements in SERS and SPR sensing, as well as a new type of nanowire-based SPP sensor

Highly directional bottom-up 3D nanoantenna for visible light

Controlling light at the nanoscale is of fundamental importance and is essential for applications ranging from optical sensing and metrology to information processing, communications, and quantum optics. Considerable efforts are currently directed towards optical nanoantennas that directionally convert light into strongly localized energy and vice versa. Here we present highly directional 3D nanoantenna operating with visible light. We demonstrate a simple bottom-up approach to produce macroscopic arrays of such nanoantennas and present a way to address their functionality via interaction with quantum dots (QDs), properly embedded in the structure of the nanoantenna. The ease and accessibility of this structurally robust optical antenna device prompts its use as an affordable test bed for concepts in nano-optics and nanophotonics applications

Plasmon Hybridization Reveals the Interaction between Individual Colloidal Gold Nanoparticles Confined in an Optical Potential Well

The understanding of interaction forces between nanoparticles in colloidal suspension is central to a wide range of novel applications and processes in science and industry. However, few methods are available for actual characterization of such forces at the single particle level. Here we demonstrate the first measurements of colloidal interactions between two individual diffusing nanoparticles using a colorimetric assay based on plasmon hybridization, that is, strong near-field coupling between localized surface plasmon resonances. The measurements are possible because individual gold nanoparticle pairs can be loosely confined in an optical potential well created by a laser tweezers. We quantify the degree of plasmon hybridization for a large number of individual particle pairs as a function of increasing salt concentration. The data reveal a considerable heterogeneity at the single particle level but the estimated average surface separations are in excellent agreements with predictions based on the classical theory of Derjaguin, Landau, Verwey, and Overbeek