Optical Tweezers Wiki Page
Our Setup: Red fiber-coupled diode laser, 70mW at 637nm. 100X, 1.3NA, 0.20mmWD oil immersion microscope objective. 150W Halogen fiber-bundled output light source. CCD camera with video-capture card and computer.
See 5um spheres on video monitor.
Movies of tweezers in action ->
5um diameter silica spheres.
Schematic of setup.
Brownian Motion Trap Stiffness
MeasurementParticles suspended in liquid exhibit random
movement due to collisions with the moving
molecules that make up the liquid. This
phenomenon is known as Brownian motion.
The equipartition theorem states that a
molecule in thermal equilibrium has an average
kinetic energy for each degree of freedom.
Assuming that the movement of the trapped
bead is due only to thermal fluctuations, we can
set the kinetic energy equal to the potential
energy of the trap:
Where <x2> is the time-averaged square of the
bead’s horizontal displacement from the center
of the trap.
On the Theory of Brownian Motion (pdf)
Optical-Tweezers Presentation (pdf)
Optical Tweezers
Links:
Optical Tweezers - Wiki