High nonlinear optical coefficient (χ3=10−7 esu) of cyanine dye J aggregates doped silica film synthesized by a simple sol–gel method

We have synthesized, for the first time, a thin silica film doped with condensed J aggregates of 1,1′-diethyl-2,2′-cyanine bromide dye using a simple sol–gel method. The film is homogeneous in thickness and stable at room temperature. The J band formed in the spin coating process is independent of polarizer angle and the film is isotropic without any dichroism. The high optical nonlinearity (χ3=5.0×10−7 esu) of the film at the resonance wavelength (=577 nm) of the J aggregates was first observed by Z-scan using a 180 fs pulse laser at 77 K under a vacuum (<10−5 torr). The doping ratio of J aggregates in silica film suggests that the net ∣χ(3)∣ value of pure J aggregates is 4.0×10−6 esu. Preliminary experiments using a pump-probe showed the film to have a response time τ of 0.5 ps under 575 nm excitation at room temperature. Since the J aggregates are incorporated into the silica film, further research is likely to lead to improved stability.