Light can exert force on physical objects. In optical trapping this is used to immobilize objects (often beads) in a focussed laser beam. These videos describe the principles of optical traps, show how to build and calibrate optical traps and show how optical traps are used in the study of molecular motors.
- Which of the following is false for optical trapping of particles that are greater than the wavelength of light?
- Can be better described by refraction of light by the particle than by an induced dipole of particle by interacting with light.
- Requires focused light from a high numerical aperture objective
- The particle is trapped at the center of the beam and slightly above the focus (between the focus and coverslip)
- Conservation of momentum can be used to explain the forces acting upon a particle in an optical trap.
- True or false. A highly reflective particle makes it easier to trap.
- For particles that are considerably smaller than the wavelength of light, which of the following is true:
- The light induces a dipole momentum in the particle,
- The dipole will move if the electromagnetic field of the light beam is non-homogeneous; ie towards a more intense region of illumination at center of a focused beam of light.
- The particle will gain momentum if it absorbs light.
- Small particles do not have appreciable scattering.
- Filling the back of the objective with light is important for trapping because
- It allows for optical trapping in the x-y plane
- It reduces light absorption by the particle.
- The momentum change of lateral light rays interacting through the particle generates forces that counter the scattering forces to allow stable optical trapping
- It provides a better means of increasing laser intensity than turning up the laser power
Dr. Bustamante received his B.S. in biology from Cayetano Heredia Universtiy in Lima, Peru, and his M.S. in biochemistry from San Marcos University, also in Lima. He then moved to the University of California, Berkeley where here completed his Ph.D. in biophysics. Currently, Dr. Bustamante is a Howard Hughes Medical Institute Investigator and a Professor… Continue Reading