Light-force sensor and method for measuring axial optical-trap forces from changes in light momentum along an optic axis

摘要

An optical trap and method for measuring both transverse and longitudinal forces on a trapped particle. Laser light sources generate first and second light beams that are focused to the trap region in a counter-propagating manner for trapping the particle. Detectors measure changes in power deflections of the light beams leaving the trap region, and changes in power concentrations of the light beams leaving the trap region. A processor calculates the transverse forces on the particle based upon the measured changes in the power deflections of the light beams, and calculates the longitudinal forces on the particle based upon the measured changes in the power concentrations of the light beams. A single beam optical trap and method are also disclosed, where the second optical beam is generated by a reflection of the first optical beam off of the trapped particle.