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SUMMARY:Laser Manipulation in Liquid Crystals: an approach to microfluidic
 s and micromachines - Prof Helen Gleeson\, Manchester Centre for Nonlinear
  Dynamics\, Manchester University
DTSTART:20061103T141500Z
DTEND:20061103T151500Z
UID:TALK5205@talks.cam.ac.uk
CONTACT:Dr Kalin Dragnevski
DESCRIPTION:Laser trapping of particles in three-dimensions can occur as a
  result of the refraction of strongly focused light through micron-sized p
 articles.  The use of this effect to produce laser tweezers is extremely c
 ommon in fields such as biology\, but it is only relatively recently that 
 the technique has been applied to liquid crystals.  The possibilities are 
 exciting: droplets of liquid crystals can be trapped\, moved and rotated i
 n an isotropic fluid medium\, or both particles and defects can be trapped
  and manipulated within a liquid crystalline medium.  This talk considers 
 both possibilities.  The mechanism of transfer of optical angular momentum
  from circularly polarised light to small droplets of nematic liquid cryst
 als is described.  Further\, it is shown that droplets of chiral liquid cr
 ystal can be made to rotate when illuminated with linearly polarised light
  and possible mechanisms are discussed.  The trapping and manipulation of 
 micron sized particles in an aligned liquid crystal medium is used to prov
 ide a measure of local shear viscosity coefficients and a unique test of t
 heory at low Erickson number in liquid crystals.
LOCATION:IRC in Superconductivity Seminar Room\, Cavendish Laboratory
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