Observation and characterization of nonlinear processes in organic and biological samples by excited state absorption (ESA) spectroscopy

By excited state absorption (ESA) spectroscopy, electronic transitions from the first excited states to higher ones are probed. These transitions are often much more sensitive to the environment of the specimen under investigation than ground state absorption spectra as well as fluorescence spectra. Therefore ESA spectroscopy on intermolecular interactions becomes a candidate for efficient biochemical sensors. In addition, many applications where fluorescence probes are used today may be improved in future regarding sensitivity and speed by the use of ESA, because absorptive measurements principally allow much faster detection in comparison to fluorescence.