Summer Undergraduate Research Fellowships

Department of Physics

University of Toronto

SURF: AFM/OPT

Coordinator: David Bailey

Lasers can be used to manipulate small particles, or to measure small displacements. This project involve understanding and improving our optical tweezers experiment, and developing new LabView control software for new Atomic Force Microscope.

Two students will work on this project.

Specific Safety Issues

• A dangerous invisible laser beam, delicate components, chemicals.
• Must receive appropriate laser safety training

Optical Tweezers

1. Become familiar with existing Thorlabs Optical Tweezers experiment, and review our existing studies of the system.
• Carefully follow instructions to avoid damage to equipment or yourself.
• Confirm beam is fully enclosed (except at focal point).
2. Study trapping of various size spheres, measuring trapping potential as a function of intensity, trying to understand currently observed unexplained variations.
   • In addition to thermal motion method, may want to try study response of bead to moving trap. Need to think if this might provide additional information. This requires borrowing stage controller from AFM.
   • Possible causes of the variations could be related to:
   • Vertical position of bead; is it close to slide or cover slip?
   • Larger than expected variations in bead sizes. Can we measure bead mass and radius?
   • Local viscosity variations in fluid.
3. Can diffraction patterns be used to measure height of sphere above the slide?
4. Investigate how to obtain or simply create other interesting samples, e.g. DNA attached to slide, but with bead at other end.

Atomic Force Microscope

1. Read about principles of Atomic Force Microscopy.
2. Review our existing studies of the system.
3. Confirm system works.
4. Start learning LabView. (Lego MindStorms robotics use related software.)
5. Convert and document existing LabWindows/CVI control software to LabView/VI. Unfortunately, this conversion must be done by hand, although the instrument drivers can be converted by the LabVIEW Instrument Driver Import Wizard.
• x,y,z stage control
• NanoMax MAX311 stage controlled through THORLABS T-Cube USB Controller Hub
• OTcontroller.vi should exist
• photodetector readout
• Control panels
• Image display

Some additional resources:

• "Optical tweezers for undergraduates: Theoretical analysis and experiments", M. S. Rocha, Am. J. Phys. 77 (8), August 2009.
• "Faster, cheaper, safer optical tweezers for the undergraduate laboratory", John Bechhoefer and Scott Wilson, Am. J. Phys. 70 (4), April 2002.

Links:

• Advanced Physics Lab
• Advanced Physics Lab Optical Tweezers Experiment
• Optical TrappingTA Manual

Last updated on 10 March 2012