An experimental characterization of the 3D forces, acting on a trapped polystyrene bead in a counter-propagating beam geometry, is reported. Using a single optical trap with a large working distance (in the BioPhotonics Workstation), we simultaneously measure the transverse and longitudinal trapping force constants. Two different methods were used: The Drag force method and the Equipartition method. We show that the counterpropagating beams traps are simple harmonic for small displacements. The force constants reveal a transverse asymmetry as - = 9.7 pN/µm and + = 11.3 pN/µm (at a total laser power of 2x35 mW) for displacements in opposite directions. The Equipartition method is limited by mechanical noise and is shown to be applicable only when the total laser power in a single 10 µm counter-propagating trap is below 2x20 mW.
|Journal||Proceedings of SPIE, the International Society for Optical Engineering|
|Publication status||Published - 2010|
|Event||SPIE NanoScience + Engineering 2010, The International Society for Optical Engineering (SPIE), 2010 - San Diego, California, USA|
Duration: 1 Jan 2010 → …
|Conference||SPIE NanoScience + Engineering 2010, The International Society for Optical Engineering (SPIE), 2010|
|City||San Diego, California, USA|
|Period||01/01/2010 → …|