Multiphoton-excited fluorescence imaging and photochemical modification ofdye-doped polystyrene microsphere arrays

The use of nonlinear optical methods for thin-film polymeric materials modi fication and characterization is explored. Ordered S-dimensional (3-D) dye- doped polystyrene microsphere arrays are photobleached and imaged in these studies. Efficient, irreversible photochemical bleaching of the dye within individual 0.5 and 1 mu m diameter microspheres occurs when 810 nm light fr om a mode-locked Ti:sapphire laser is focused to an similar to 400 nm diame ter spot within the spheres. Photobleaching is shown to result from three-p hoton absorption and may involve ionization of the dye. The three-photon-in duced photochemistry is dramatically more efficient than that resulting fro m single-photon excitation. Imaging of the unbleached and bleached arrays i s accomplished by monitoring the two-photon-excited fluorescence from the d ye. Both the nonlinear photobleaching and imaging methods provide inherent depth-discriminating capabilities, allowing for high-resolution 3-D control of the volume modified and imaged. The results suggest that the methods an d materials employed here may have important optical data storage applicati ons. The capabilities of these methods are demonstrated by bleaching indivi dual spheres in 3-D arrays, without affecting neighboring spheres. Optical data storage densities as high as 10(13) bits/cm(3) are readily achievable. Unique photobleaching patterns observed within the spheres are explained b y the radiation distribution within individual microspheres under focused-b eam illumination.