off-resonant four-wave mixing
'degenerate' four-wave mixing (DFWM) experiments were performed on gaseous
samples. By delaying one pulse a periodic recovery of the DFWM signal
is observed. From the period of the transients the observed experimental
findings can be unambiguously assigned to Raman transitions within the
laser bandwidth. Rotational constants of the molecules can be determined
accurately. The decay of the transients yields the collisional dephasing
of the Raman-induced polarization. At zero delay also optical-field-induced
birefringence of electronic nature contributes to the signal. The application
of the technique to molecular beam experiments and to molecules of lower
symmetry (CHCl3,SO2) has been demonstrated.
 H.-M. Frey, P. Beaud, T. Gerber, B. Mischler, P. Radi, A. Tzannis, Appl. Phys. B 68, 735, 1999.
 H.-M. Frey, P. Beaud, T. Gerber, B. Mischler, P. Radi, A. Tzannis, J. of Raman Spectrosc., 31, 71, 2000.
 B. Lavorel, H. Tran, E. Hertz, O. Faucher, P. Joubert, M. Motzkus, T. Buckup,
T. Lang, H. Skenderovi, G. Knopp, P. Beaud, H.-M. Frey, C.R. Physique, 5, 215-229, (2004).
Figure: Four wave mixing signal versus time delay of the probe pulse for Lab-air at
room temperature and for atmospheric pressure cells of poor O2,
N2 and CO2.