Microengines have shown promise for a variety of applications in nanotechnology, from microfluidics to nanomedicine and targeted drug delivery. However, their precise control over their dynamics is still challenging. We introduce a micro engine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that a gold-silica Janus particle illuminated by a high focused laser beam can be confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light the symmetry between these forces can be broken by transferring angular momentum to the particle, resulting in a tangential force that induces an orbital motion of the particle. We can simultaneously control the velocity and direction of rotation of the particle, changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. We validate our results using a geometrical optics model that incorporates optical force, the absorption of optical power, and the resulting heating of the particle.
Optical nano-printing provides a versatile platform to print various nanoparticles into arbitrary configurations. Optical printing, the use of light to direct the formation of a desired structure, has been of significant interest in the last two decades. For particles much smaller than the laser wavelength, optical forces can be well described in the dipole approximation. For a focused laser beam, two main optical force components are identified: the gradient force, which attracts particles toward the high-intensity focal spot, and the scattering force, which tends to push particles along the beam propagation direction. When the wavelength light is close to the particle localized surface plasmons resonance, a scattering force is dominant and can be used to efficiently push nanoparticles along the beam optical axis onto a substrate. In this context, optical forces can be applied to optically print nanoparticles into patterns aggregated on surfaces such as glass. Here, we report on use optical nanoprinting of plasmonic nanoparticles to create an active aggregate in a solution containing dyes or nanoplastics. The active aggregate, produced by optical forces, serves as a sensitive sensor which is used to detect dyes in concentrations below the limit of detection for Raman spectroscopy and/or to detection of plastic nanoparticles.
Cosmic dust particles are usually collected in space or in the Earth’s stratosphere and deposited on a substrate to be analysed at large terrestrial facilities.
We use Raman tweezers technique for the contacless manypulation of cosmic dust particles, to identify their compositions and to characterize their response to optical forces without any substrate effects, documenting the high potential of this novel technique for space exploration.
Electrospinning technologies for the realization of active polymeric nanomaterials can be easily up-scaled, opening perspectives to industrial exploitation, and due to their versatility they can be employed to finely tailor the size, morphology and macroscopic assembly of fibers as well as their functional properties. Light-emitting or other active polymer nanofibers, made of conjugated polymers or of blends embedding chromophores or other functional dopants, are suitable for various applications in advanced photonics and sensing technologies. In particular, their almost onedimensional geometry and finely tunable composition make them interesting materials for developing novel lasing devices. However, electrospinning techniques rely on a large variety of parameters and possible experimental geometries, and they need to be carefully optimized in order to obtain suitable topographical and photonic properties in the resulting nanostructures. Targeted features include smooth and uniform fiber surface, dimensional control, as well as filament alignment, enhanced light emission, and stimulated emission. We here present various optimization strategies for electrospinning methods which have been implemented and developed by us for the realization of lasing architectures based on polymer nanofibers. The geometry of the resulting nanowires leads to peculiar light-scattering from spun filaments, and to controllable lasing characteristics.
We present the result of an investigation into the optical trapping of micropaticles using laser beams with a spatially inhomogeneous polarization (cylindrical vector beams). We perform three-dimensional tracking of the Brownian fluctuations in position of a trapped particle and extract the trap spring constants. We characterize the trap geometry by the aspect ratio of spring constants in the directions transverse and parallel to the beam propagation direction and evaluate this figure of merit as a function of polarization angle. We show that the additional degree of freedom present in cylindrical vector beams (CVBs) allows us to control the optical trap strength and geometry by adjusting the polarization of the trapping beam only. Experimental results are compared with a theoretical model of optical trapping using CVBs derived from electromagnetic scattering theory in the T-matrix framework.
We investigate experimentally and theoretically plasmon-enhanced optical trapping of metal nanoparticles. We calculate
the optical forces on gold and silver nanospheres through a procedure based on the Maxwell stress tensor in the transition
T-matrix formalism. We compare our calculations with experimental results finding excellent agreement. We also
demonstrate how light-driven rotations can be generated and detected in non-symmetric nanorods aggregates. Analyzing
the motion correlations of the trapped nanostructures, we measure with high accuracy both the optical trapping
parameters, and the rotation frequency induced by the radiation pressure.
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