Gradient Force ：
Gradient of the medium from the small ball in the electric dipole moment in the uneven field by the force. It is proportional to the light intensity gradient, at the light intensity of the largest. Its effect makes optical power density of particles towards the biggest point movement. Gradient force proportional to the light intensity gradient, at the light intensity gradient direction.
Scattering Force：
Coal-in the uneven spread, as part of light is not directly forward, scattering in all directions will be open to a scattering phenomenon, the length of the wave scattering more. From the scattering of light in the process of scattering and photon momentum exchange obtained by the scattering of photons change the momentum of the photon from the media force. It along the direction of light propagation direction, making the effect of the particles along the beam propagation direction of movement. Proportional to the scattering of radiation intensity, at the direction of the beam propagation direction.
In fact, when light through the ball, the ball surface would produce a certain reflection, small balls of light absorbed to a certain extent, this will exert a thrust on the ball, often referred to as the power of scattering (Fs ). Scattering of light along the direction of pushing always run particles, and the gradient of particles is to drag the focus point of the beam. Optical Trap relies mainly on the formation of optical gradient force. Capture is a stable gradient force and scattering of a balanced outcome. Only near the focus of the scattering of more than gradient force, to form a three-dimensional optical trap to capture particulate and stable. In other words, such a beam can be as gripping as tweezers particles, mobile and particulate control.