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.
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