of John and Steffen's project was to study the
trapping of microscopic bubbles in an optical tweezers, and the factors
affect the magnitude of the trapping force, such as laser power, bubble
and trap size and geometry.
microbubbles are a commercially available ultrasound
contrast agent, and have diameters of up to 10 mm.
They are interesting to trap because their refractive index is lower
that of the suspending fluid, so they are repelled from the part of the
with highest intensity.
Contact Phil Jones if
you are interested in a BSc, MSci or MSc project for the coming year
Hilgemann operating the optical tweezers
overcome this by rapidly scanning the laser beam in a
circle such that the bubbles experience a time-averaged trap that is a
volume surrounded by higher intensity in all
picture below shows two optically trapped microbubbles in
the tweezers, demonstrating that they may be manipulated in all three
Wright preparing microbubbles on a microscope slide
John and Steffen's results
helped us to determine how the optical trapping force depends on the
microbubble and trap size, finding that the efficiency of the trap (in
the axial direction) is
Some of the data from this
project appeared in a paper in a
special issue of the Journal of Optics A (2007).
microscopic bubbles being manipulated in the optical tweezers