Researchers from the Universität Würzburg in Germany have discovered that selective excitation of individual molecule types in a heterogeneous solution, while not attainable through manipulation of single parameters such as wavelength or linear chirp control, is possible through adaptive femtosecond pulse shaping.

The team used a combination of a pulse shaper and an automated "learning loop" algorithm to selectively excite one of two similar -- yet chemically distinct -- dye molecules suspended in the same solution. The pulse shaper used spectral phase modulation to vary laser fields based upon a signal from the algorithm, which used feedback from the solution to find laser fields optimized for the molecular excitation.

The researchers, who reported their results in the Nov. 1 issue of Nature, suggest that this method should be useful in any situation where chemically selective excitation is required, such as bimolecular reaction control and multiphoton fluorescence microscopy.