Keen, Stephen Alexander Juhani
(2009)
High-speed video microscopy in
optical tweezers.
PhD thesis, University of Glasgow.
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Abstract
Optical tweezers have become an invaluable tool for measuring and
exerting forces in the pico-Newton regime. Force measurements have
in the past concentrated on using only one trapped particle as a
probe, partly due to the difficulties in tracking more than one par-
ticle at high enough frame rate. Recent advances in video camera
technology allow the collection of images at several kHz. However,
there has been little use of high-speed cameras in optical tweezers,
partly due to data management problems and affordability. This the-
sis presents seven experiments carried out during my PhD involving
the use of several different high-speed cameras.
Chapter 3 presents the use of a CMOS high-speed camera with in-
tegrated particle tracking built by Durham Smart Imaging. The
camera was used in a Shack-Hartmann sensor setup to determine
rapidly and non-ambiguously the sign and magnitude of the orbital
angular momentum of a helically-phased beam light beam, as an
alternative to interferometric techniques. Chapter 4 presents a di-
rect comparison of a CCD high-speed video camera with a quadrant
photodiode to track particle position. Particle tracking was possible
at high enough accuracy and bandwidth to allow convenient trap
calibration by thermal analysis. Chapter 5 reports an investigation
of the resulting change in trap stiffness during the update of trap
positions in holographic optical tweezers. Chapter 6 presents the re-
sults from using a high-speed camera to successfully track multiple
particles in a microfluidic channel to measure the viscosity at sev-
eral points simultaneously. The last three chapters investigate the
hydrodynamic interactions between trapped particles under different
conditions and comparisons were made with theory.
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