High-resolution axial and lateral position sensing using two-photon excitation of fluorophores by a continuous-wave Nd:YAG laser

Author :Ernst-Ludwig Florin, J. K. Heinrich Ho¨ rber, and Ernst H. K. Stelzer
Publication :Applied Physics Letters
Volume :69
Number :4
Pages :446-448
Year :1996

The change in position of fluorescent beads captured inside the focal volume of optical tweezers is
monitored using fluorescence emission induced by two-photon absorption of a continuous-wave
Nd:YAG laser ~l51064 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 position of a CY3-labeled latex bead with a diameter of 1.03 mm to a precision
better than 10 nm. At an intensity of 600 mW/ mm2 the two-photon bleaching rate is lower than 50%
per 2000 s.