Switching nanoscale temperature fields with high-order plasmonic modes in transition metal nanorods.

Depending on the photoirradiation conditions, metal nanostructures exhibit various plasmonic modes, including dipolar, quadrupolar, and hexapolar modes. This work demonstrates numerically that these high-order plasmonic modes can be used to switch nanoscale temperature distributions during the plasmonic heating of a manganese (Mn) nanorod. The key feature of Mn is its low thermal conductivity.

Fluctuation-mediated orbital rotation of microparticles in non-coaxially counter-propagating optical tweezers.

We have demonstrated in the present report that dielectric microparticles exhibited orbital rotation in the light field of non-coaxially configured two counter-propagating laser beams both in numerical simulations and experiments. A series of computational simulations indicated that when irradiated with two non-coaxially counter-propagating parallel laser beams with the same intensity distributions in the absence of thermal (Brownian) motion, a microparticle did not exhibit orbital rotation due to the symmetry of the optical field. However, the computations predicted that a microparticle exhibited one directional orbital rotation in the presence of thermal motion because of the symmetry breaking of the optical force acting on the particle.

Plasmonic nanoscale temperature shaping on a single titanium nitride nanostructure.

Arbitrary shaping of temperature fields at the nanometre scale is an important goal in nanotechnology; however, this is challenging because of the diffusive nature of heat transfer. In the present work, we numerically demonstrated that spatial shaping of nanoscale temperature fields can be achieved by plasmonic heating of a single titanium nitride (TiN) nanostructure. A key feature of TiN is its low thermal conductivity ( = 29 [W m K]) compared with ordinary plasmonic metals such as Au ( = 314 [W m K]).

Opto-thermophoretic separation and trapping of plasmonic nanoparticles.

Optical tweezers are powerful tools to trap, transport, and analyse individual nano-objects at dilute concentrations. However, it is still challenging to manipulate isolated single nano-objects in dense target environments with various kinds of materials, such as in living cells and mixtures of nanocolloids. In the present work, we have succeeded in the selective trapping of a few gold nanoshells with specific sizes and sweeping others out completely, only by irradiating the dense colloidal suspension of gold nanoshells with a focused near infrared continuous-wave (CW) laser.

Mesoscopic Motion of Optically Trapped Particle Synchronized with Photochromic Reactions of Diarylethene Derivatives.

Not only the energy but also the momentum of photons transfers to material via photoabsorption; this momentum transfer, known as radiation pressure, can induce motions of small particles. It can therefore be expected to induce mechanical motions of mesoscopic materials synchronized with the reversible change of their absorption coefficient by external stimuli. We demonstrated quantitative photomechanical motions in mesoscopic regions by combining optical tweezer and photochromic reactions of diarylethene (DAE).

Plasmonic Control and Stabilization of Asymmetric Light Scattering from Ag Nanocubes on TiO.

When plasmonic nanoparticles are placed on a highly refractive semiconductor substrate, we can expect three different effects: (i) resonance mode splitting, (ii) asymmetric light scattering based on the split modes, and (iii) site-selective nanoetching due to plasmon-induced charge separation (PICS) at the nanoparticle-semiconductor interface. Here, we develop novel photofunctional materials by taking advantage of those three effects. More specifically, we control the asymmetric scattering of Ag nanocubes on TiO by PICS, so as to develop materials for photodrawing of one-way visible translucent images and multicolor scattering images.

Stationary bubble formation and Marangoni convection induced by CW laser heating of a single gold nanoparticle.

Gold nanoparticles (Au NPs) efficiently convert incident light into heat under the resonant conditions of localized surface plasmon. Controlling mass transfer through plasmonic heating of Au NPs has potential applications such as manipulation and fabrication within a small space. Here, we describe the formation of stationary microbubbles and subsequent fluid convection induced by CW laser heating of Au NPs in water.

Stepwise Two-Photon-Induced Fast Photoswitching via Electron Transfer in Higher Excited States of Photochromic Imidazole Dimer.

Stepwise two-photon excitations have been attracting much interest because of their much lower power thresholds compared with simultaneous two-photon processes and because some stepwise two-photon processes can be initiated by a weak incoherent excitation light source. Here we apply stepwise two-photon optical processes to the photochromic bridged imidazole dimer, whose solution instantly changes color upon UV irradiation and quickly reverts to the initial color thermally at room temperature. We synthesized a zinc tetraphenylporphyrin (ZnTPP)-substituted bridged imidazole dimer, and wide ranges of time-resolved spectroscopic studies revealed that a ZnTPP-linked bridged imidazole dimer shows efficient visible stepwise two-photon-induced photochromic reactions upon excitation at the porphyrin moiety.

Laser-driven phase transitions in aqueous colloidal gold nanoparticles under high pressure: picosecond pump-probe study.

Pump-probe transient extinction spectroscopy was used to analyze 355 nm picosecond laser heating-induced phenomena in 60 nm-diameter aqueous gold nanoparticles (AuNPs) under a high pressure of 60 MPa. Kinetic spectroscopy revealed that a supercritical layer surrounding the AuNP nucleated with a lifetime of approximately 1 ns during its dynamic expansion and decay for a fluence of 19.6 mJ cm(-2).

CW-laser-induced morphological changes of a single gold nanoparticle on glass: observation of surface evaporation.

Pulsed-laser heating of colloidal noble-metal nanoparticles in an aqueous solution induces morphological changes such as size reduction. However, the technique suffers disadvantages through polydispersed products. Here, we show that continuous-wave (CW) laser heating of single gold nanoparticles is capable of generating particles of smaller diameters with superb control in terms of exposure time and intensity.

Picosecond-to-nanosecond dynamics of plasmonic nanobubbles from pump-probe spectral measurements of aqueous colloidal gold nanoparticles.

The photothermal generation of nanoscale vapor bubbles around noble metal nanoparticles is of significant interest, not only in understanding the underlying mechanisms responsible for photothermal effects, but also to optimize photothermal effects in applications such as photothermal cancer therapies. Here, we describe the dynamics in the 400-900 nm regime of the formation and evolution of nanobubbles around colloidal gold nanoparticles using picosecond pump-probe optical measurements. From excitations of 20-150 nm colloidal gold nanoparticles with a 355 nm, 15 ps laser, time-dependent optical extinction signals corresponding to nanobubble formation were recorded.

Observation of nanoscale cooling effects by substrates and the surrounding media for single gold nanoparticles under CW-laser illumination.

Understanding the nanoscale heating-induced local thermal response is important but hampered by lack of information on temperatures at such small scales. This paper reports laser-induced heating and thermal equilibration of metal nanoparticles supported on different substrates and immersed in several media. We use single-particle spectroscopy to monitor nanoparticle temperature rises due to laser excitation.