We demonstrate coherent control of isotope selective fragmentation processes of potassium dimers into differing atomic isotopes using shaped fs-laser pulses. When applying evolution strategies in a feedback loop, optimizing K-39(+) VS. K-41(+) for different center wavelengths, we astonishingly exposed molecular fingerprints. Moreover, we performed two criteria optimizations by maximizing the fragment vs. the dimer ion isotope ratio with selected weighting factors. Insight into the coherent ultrafast interaction of spectral pulse components with the dimer wave functions is provided by analyzing the optimized pulse forms. (c) 2005 Elsevier B.V. All rights reserved.