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 vi brational wave packet dynamics in the electronic ground state of cold K-2 m olecules. A spectral analysis of the time domain signal reveals two differe nt wave packet contributions: one from a stimulated Raman process and one f rom stimulated emission pumping. Also femtosecond time-resolved degenerate four-wave mixing (DFWM) spectroscopy is performed in order to investigate m olecular dynamics in iodine molecules in the gas phase. Depending on the ti ming of the laser pulses different dynamics are reflected in the DFWM trans ient signal. By the use of time-evolution diagrams, the varying contributio n of ground and excited state dynamics can be explained conclusively. (C) 1 999 Elsevier Science B.V. All rights reserved.