Optical gate action of a molecular thin film probed with femtosecond near-field optical microscopy

We have combined a near-field scanning optical microscope with a two-color time-resolved pump-probe measurement system. The sample was a molecular thi n film that revealed an excitonic resonance and also had a characteristic d omain structure. The measurement system has a noise-equivalent transmittanc e change as small as 5.0x10(-5) for a probe pulse with an intensity of 30 n W, which allows us to detect an optical gate action of a single domain. The results suggest that the film composition is uniform over a distance of se veral microns while it may vary on a greater scale. (C) 2000 American Insti tute of Physics. [S0003-6951(00)00135-2].