KEYWORDS: Optical Tweezers, Birefringent particles, Biophysics.
Optical tweezers is a very useful tool in physics, chemistry and biology. Although the
translational motion of trapped particles is extensively studied, exploration of the rotational
motion has started more recently. Of the rotations, in-plane or yaw motion has been developed
over the last couple of decades. The other rotations, like the pitch and the roll, are less
investigated compared to the yaw. In this work, we study the rotations of the birefringent
particle. Firstly we explore the yaw motion and then explore the first out-of-plane rotation
which we call the pitch motion in the nomenclature of the airlines.
At the beginning of the work, we look for the suitability of the cylindrical approximation for
spherical particles executing yaw rotation in the first chapter [1]. Then we find new methods
to generate yaw rotations with low ellipticity beams [2]. After that, we move on to apply the
rotations to study soft matter systems. We study the adhesivity of surfaces using yaw rotations
[3] and then move on to detect pitch motion at high resolution to explore cell biological
applications [4]. Lastly, we use the translation motion of a particle to calibrate optical tweezers
inside cells [5] in view of the rotational calibration which is beyond the scope of this thesis.
1. Rahul Vaippully, Venkata Siva Gummaluri, C Vijayan and Basudev Roy, “Validity of cylindrical
approximation for spherical birefringent microparticles in rotational optical tweezers”, Journal of
Physics Communications, 4, 015005 (2020).
2. Rahul Vaippully, Muruga Lokesh and Basudev Roy, “Continuous rotational motion in birefringent
particles using two near-orthogonally polarized optical tweezers beams at different wavelengths with
low ellipticity.” Journal of Optics, 23, 094001(2021)
3. Rahul Vaippully, Dhanush Bhatt, Anand Dev Ranjan and Basudev Roy, “Study of adhesivity of surfaces
using rotational optical tweezers”, Physica Scripta, 94, 105008 (2019).
4. Rahul Vaippully, Vaibavi Ramanujan, Manoj Gopalakrishnan, Saumendra Bajpai and Basudev Roy,
“Detection of sub-degree angular fluctuations of the local cell membrane slope using optical tweezers”,
Soft Matter, 16, 7606 (2020).
5. Rahul Vaippully, Vaibavi Ramanujan, Saumendra Bajpai and Basudev Roy, “Measurement of viscoelastic
properties of the cellular cytoplasm using optically trapped Brownian probes”, Journal of Physics
Condensed Matter , 32, 235101 (2020).