Progress toward Using an Optical Tweezer to Make Scattering-based Size Measurements

Matt Damon

2012

Knowing the size of an object is a crucial weapon in the arsenal of physics, but what about objects that are so small they cannot be measured by simply using a meter stick or another physical measuring device? One way to determine the size of these small ob jects is to study the scattering patterns they create when light is scattered off them. There are many different physical setups that could be used to study these scattering patterns, but this experiment focused on just one, optical tweezers. In an optical tweezers setup a small particle is trapped at the focus of a laser, making this setup ideal for studying the scattering patterns caused by that particle. Once the scattering patterns are recorded these scattering patterns must be compared to computer simulations to determine the size of the particle. The computer simulations were created using Complex Focus (CF) fields because CF fields allowed for multiple simulations to be created with all variables held constant, except the size of the particle. The experimental scattering pattern could then be compared to the CF field simulation and whichever simulation the experimental scattering pattern matched the best determined the size of the particle. Determining the size of particles with an optical tweezers setup was the ultimate goal of this experiment, but this goal was not achieved for various reasons. Instead this experiment will provide vital experience for future experiments.