Optical trapping and rotation of resonant nanoparticles combined with determination of its internal and external temperatures create a perfect platform for study of rheology, temperature and basic thermodynamics in the micro- and nanoscale.
The optically powered train of microparticles waveguide the light, stabilized itself and move forward due to strong optical forces. This phenomenon is similar to the soliton creation in microparticles solution, but here particles develop one after another from the reservoir in direction of light propagation, similarly to a chain developing from a spool or a train. We experimentally study the effect and numerically evaluate the forces acting on microparticles in the chain. We find different regimes of behavior depending on the microparticles size.
The optical train of microparticles waveguide the light and stabilized itself due to strong optical and hydrodynamic forces. Particles develop one after another from the reservoir in direction of light propagation similarly to a chain developing from a spool or a train. We experimentally study the effect and numerically evaluate the forces acting on micorparticles in the train. When number of particles in reservoir is small we observe rapid shooting of microparticles like from the optically powered cannon.
In light absorbing liquids optical trapping of solid micro-objects but also gas bubbles can be achieved and explained by the mechanisms involving the hydrodynamic whirls formation. The various forms of these whirls, that arise due to optothermal Marangoni effect induced by laser light beam, are able to accelerate the objects movement, transport them and subsequently trap at the laser beam center but also close to it. The usual light gradient field force and scattering force solely are insufficient and even not adequate to properly describe the mentioned by us particle trapping effects as the trap potential extends to much larger distances that the beam waist. We will demonstrate the mechanism of optical trapping and transporting of gas bubbles and will discuss the physics of whirls formation in this case. The numerical modelling of Marangoni flows at the liquid-gas interface confirms the experimental findings. We also demonstrate a novel type of trapping of micro-objects that occurs inside a toroidal whirl induced by laser in dye-doped oil. This type of trapping is quite unusual but allows to transport objects immobilized far from the beam waist just avoiding their excessive heating.
Optical trapping is a widely used technique allowing for remote and precise manipulation of particles and measurement of forces acting on them. It also gives possibility of measuring viscosity, by analyzing the Brownian motion, and temperature by analyzing Raman scattering or luminescence of trapped particle. Large variety of nanoparticles including resonant one, like plasmonic and high-index dielectric, and non-resonant, like rare earth ions doped nanocrystals, and their hybrid combination makes them excellent probes for thermo-rheological measurements in microliter volumes and basic thermodynamic studies in nanoscale. Resonant nanoparticles, which strongly interact with light, allow better control of position and orientation, and give possibility of rapid rotation due to large optical forces and torques acting on them. The same property makes their optical trapping in 3D challenging and limited to a narrow size range due to the strong radiation pressure.
Here, we show how large plasmonic nanorods can be optically trapped and rapidly rotate in three dimensions using focus splitting in anisotropic crystal phenomenon [1]. We also show that it is possible to optically trap and rotate silicon nanoparticles of anisotropic shape and simultaneously measure their inner temperature from Raman scattering signal and outer one from Rotational Hot Brownian Motion analysis. We use NaYF4:Er,Yb up-converting nanocrystals and their hybrid combination with gold for simultaneous heating, temperature and viscosity measurements in microliter volumes.
[1] P. Karpinski, S. Jones, D. Andren, and M. Kall, Laser Photonics Rev. 2018, 1800139.
Optical trapping is a widely used technique allowing for remote and precise manipulation of particles and measurement of the forces acting on them. Yet, it has significant limitations when it comes to particles that strongly interact with light e.g. plasmonic and high-index dielectric nanoparticles. These particles have the cross section for the light-matter interaction much larger than their physical size. This makes them perfect nanoantennas for bio-sensing, SERS, local temperature measurements, and heat-therapy. It also allows for efficient transfer of spin and orbital angular momentum of light for realization of fast nanorotors. The same property makes their optical trapping in 3D challenging and limited to a narrow size range due to the strong radiation pressure.
We use a vector beams created using optically anisotropic crystals to optically trap and spin plasmonic nanorods in 3D fashion [1]. Using different configuration of the anisotropic crystals we can create a three dimensional optical vector field for realization of complicated motion and alignment of the trapped nanorod.
We also show that the Raman signal from the optically trapped silicon nanoparticle can be used to determine the internal temperature of nanoparticle. Temperature of the medium outside the nanoparticle can be retrieved form analysis of its stochastic motion. Comparing these two temperatures and including them in the nanoscale thermodynamic calculations, we can obtain information about the interfacial thermal Kapitza resistance, and the temperature and viscosity of the media surrounding the nanoparticle.
[1] P. Karpinski, S. Jones, D. Andren, and M. Kall, Laser Photonics Rev. 2018, 1800139.
We present trial calculations of surface light-induced patterns in photochromic azo-substituted polymers. Using microscope with nanopositioning stage various birefringence and surface structures have been recorded in photochromic azo-functionalized polymers. By systematic approach to the inscription experiment and controlling cw or pulsed laser light intensity, its polarization and beam scan speed we observed the dynamics of molecular photoorientation and its relation to mass transport. We discuss properties of holographically inscribed polarization gratings and analyze them spatially by monitoring of microscopic local diffraction efficiency. We report how azo-benzene molecules can work in other systems, i.e. azobenzene functionalized POSS molecules embedded in nematic liquid crystal.
Organic nanocrystals (ONCs) similarly to inorganic ones show interesting size effects. It has been already observed that
their luminescence properties can be changed in terms of enhanced luminescence and spectral shift of fluorescence bands
as compared to bulk materials. Usually these effects are observed for much larger size of nanoparticles from 50 nm up to
1000 nm. Noncentrosymmetric and fluorescent organic crystals are rare but particularly interesting as they exhibit both
nonlinear optical properties like Second Harmonic Generation (SHG) and fluorescence. Such ONC's could serve as
fluorescent and SHG probes for bio-imaging purposes simultaneously. This could be beneficial for situation in which the
dynamics of ordering of biological systems has to be studied. Here, we report on 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-
dihydro-1H-pyrazole (DCNP) compound which forms nanocrystals, exhibits large shifts of fluorescence maximum with
size and strong SHG signals. When embedded in polymeric or biopolymeric matrix DNA-CTMA shows efficient
amplified spontaneous emission. The unique properties of this compound in its various forms from molecules, ONC's to
macroscopic single crystals are studied and discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.