Ultrafast confocal microscope for time-resolved imaging of thin films

A peculiar feature of organic semiconductors is structural inhomogeneity: in the solid state they are generally amorphous or polycrystalline, with local order only achieved in mesoscopic domains with size typically ranging from 10 nm to 1 µm [1]. The dimensions and types of these domains have a decisive influence on excited state dynamics, which in turn determines fluorescence quantum yield, charge carrier mobility and generation efficiency, crucial parameters for optimizing the efficiency of organic optoelectronic devices. Femtosecond pump-probe spectroscopy provides a wealth of information on the photophysics of organic semiconductors [2]. Experiments are usually performed over relatively large sample areas, with diameter of the order of several tens of microns, thus obtaining a macroscopic information that is averaged over many mesoscopic domains. In this paper we present a novel instrument which combines the spatial resolution of confocal microscopy with the temporal resolution and spectral sensitivity of femtosecond pump-probe spectroscopy using broadband detection.