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 thin film that revealed an excitonic resonance and also had a characteristic domain structure. The measurement system has a noise-equivalent transmittance change as small as 5.0×10−5 for a probe pulse with an intensity of 30 nW, 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 several microns while it may vary on a greater scale.