HIGH-RESOLUTION AXIAL AND LATERAL POSITION SENSING USING 2-PHOTON EXCITATION OF FLUOROPHORES BY A CONTINUOUS-WAVE ND-ALPHA-YAG LASER

The change in position of fluorescent beads captured inside the focal volume of optical tweezers is monitored using fluorescence emission in duced by two-photon absorption of a continuous-wave Nd:YAG laser (lamb da = 1064 nm). The displacement of a bead due to interactions with its environment leads to a fluorescence intensity variation that is used to design a novel spatial sensor. We determine changes in the axial po sition of a CY3-labeled latex bead with a diameter of 1.03 mu m to a p recision better than 10 nm. At an intensity of 600 mW/mu m(2) the two- photon bleaching rate is lower than 50% per 2000 s. (C) 1996 American Institute of Physics.