Abstract
Particles held in optical tweezers are commonly thought to be at
thermodynamic equilibrium with their environment. Under this assumption
the elastic energy of the trap is equal to the thermal energy. As a
result the variance of the particle position is completely independent
of viscosity and inversely proportional to the optical power in the
trap. Here we show that these conditions only hold for very high
symmetry cases e.g. perfectly spherical particles in unaberrated,
linearly polarized Gaussian traps. Here we show that any reduction in
symmetry leads to asymmetrically coupled degrees of freedom. The
associated force field is linearly non-conservative and the tweezer is
no longer at equilibrium. In overdamped systems the effect is a
underlying systematic bias to the Brownian motion. In underdamped
systems, this systematic component can accumulate momentum, eventually
destabilizing the trap. We illustrate this latter effect with reference
to two systems, (i) an isotropic sphere in a circularly polarized trap,
and (ii) a birefringent sphere in a linearly polarized trap. In both
cases the instability can be approached either by decreasing air
pressure or by increasing optical power. Close to instability, the
trapped particle executes increasingly coherent motion that is highly
sensitive to external perturbations. Potential applications to weak
force sensing are discussed.
Original language | English |
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Title of host publication | Complex Light and Optical Forces XIV |
Editors | David L. Andrews, Enrique J. Galvez, Halina Rubinsztein-Dunlop |
Publisher | SPIE |
ISBN (Electronic) | 9781510633575 |
DOIs | |
Publication status | Published - 24 Feb 2020 |
Event | Complex Light and Optical Forces XIV 2020 - San Francisco, United States Duration: 4 Feb 2020 → 5 Feb 2020 Conference number: 14 |
Publication series
Name | Proceedings of SPIE - The International Society for Optical Engineering |
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Volume | 11297 |
ISSN (Print) | 0277-786X |
ISSN (Electronic) | 1996-756X |
Conference
Conference | Complex Light and Optical Forces XIV 2020 |
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Abbreviated title | SPIE OPTO 2020 |
Country/Territory | United States |
City | San Francisco |
Period | 4/02/20 → 5/02/20 |
Keywords
- Birefringence
- Instability
- Optical force
- Spin