Optical discrimination of racemic from achiral solutions.

The use of femtosecond laser pulses to selectively trigger an asymmetric photoreaction is demonstrated in this study. Depending on the handedness of the laser polarization, more R- or S-enantiomers of a racemate are gradually destroyed, leading to the generation of enantiomeric excess. The kinetic evolution of this excess is detected with a sensitive polarimeter. Hence, discrimination between racemic and achiral solutions and selective preparation of an enantiomeric excess within seconds is achievable. Furthermore, this technique opens the possibility for quantum control with chiral substances if the laser pulses which trigger the photoreaction are adjusted by pulse-shaping techniques.