Femtosecond pump-probe and four-wave mixing spectroscopies applied to simple molecules

A femtosecond three color pump/dump-probe scheme in combination with a time-of-flight (TOF) mass selective detection unit has been applied to study vibrational wave packet dynamics in the electronic ground state of cold K-2 molecules. A spectral analysis of the time domain signal reveals two different wave packet contributions: one from a stimulated Raman process and one from stimulated emission pumping. Also femtosecond time-resolved degenerate four-wave mixing (DFWM) spectroscopy is performed in order to investigate molecular dynamics in iodine molecules in the gas phase. Depending on the timing of the laser pulses different dynamics are reflected in the DFWM transient signal. By the use of time-evolution diagrams, the varying contribution of ground and excited state dynamics can be explained conclusively. (C) 1999 Elsevier Science B.V. All rights reserved.