Optical Tweezers Project
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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 Measurement

Particles 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
beadís horizontal displacement from the center
of the trap.

On the Theory of Brownian Motion (pdf)

Optical-Tweezers Presentation (pdf)

Optical Tweezers

Optical Tweezers - Wiki