Mapping of Three-Dimension Optical Force Field on Micro-particle in Optical Tweezers

We use a pair of orthogonal tracking beams to track and analyze the Brownian motion of a micro-particle or a living cell trapped in optical tweezers to map the three-dimensional optical force field on these samples. For optical trapping with λ = 532nm, NA = 0.85, and total power = 100mW, the axial and the transverse spring constants are around 1x10
^-8
N/m and 2x10
^-8
N/m, respectively for a silica particle (diameter = 2.58 μm), and 3x10
^-8
N/m and 2x10
^-7
N/m, respectively for a Chinese hamster ovary cell (diameter ∼15 μm).