Many fundamental processes in chemistry and biology occur on extremely short time scales inaccessible by conventional analytical methods. Here we show how femtosecond transient absorption spectroscopy reveals intimate details of key molecular processes such as electron or energy transfer. We describe in detail experimental set-up and discuss various parameters necessary to obtain desired information. Application of the method is demonstrated on peridinin-chlorophyll protein from marine photosynthetic organisms, in which we follow dynamics of energy transfer between carotenoids and chlorophylls., Petr Hříbek, Marcel Fuciman, Pavel Chábera, Tomáš Polívka., and Obsahuje bibliografii