Abstract

The multiphoton fluorescence excitation observed in a continuous-wave (cw) single-beam gradient force optical trap (optical tweezers) is reported for latex beads labeled with a yellow-green fluorescent dye (BODIPY). The fluorescence emission spectra of the yellow-green beads trapped and excited by the same 1064-nm laser light are identical to the spectra excited by the 365-nm UV light. The influence of the numerical aperture of the objective on the slope of the log–log power-dependence has been demonstrated for BODIPY–Oil solution under cw and pulsed-laser conditions. The possibility that three-photon excitation process occurs is discussed within the context of a dog-bone saturation model. Other possibilities for the observed fluorescence excitation have been discussed.

© 1998 Optical Society of America

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