Vibrational climbing
Vibrational climbing allows coherent control of vibrational motion in molecules. It relies on the use of a chirped infrared pulse resonant with the targeted vibration, the pulse chirp allowing to account for the anharmonicity of the vibration. We have used intense infrared pulses, stretched through linear dispersion in dispersive materials insuring either positive (Ge) or negative (CaF2) group velocity dispersion. We thus excited the CO vibration in carboxyhemoglobin. The vibrational excitation has been evidenced by use of infrared spectrally-resolved pump-probe spectroscopy.
The above figure shows a few differential spectra measured using an infrared probe pulse delayed by 16 ps after the pump pulse. The positive peak at 1950 cm-1 corresponds to the bleaching of the v=0 to v=1 transition, while the series of negative peaks, with frequencies shifted due to the potential anharmonicity, correspond to induced absorption between excited vibrational levels. This figure shows that in the case of an appropriate chirp value (-32000 fs²), vibrational climbing allows to reach a highly excited state (here v=6). In some cases, we have also observed a population inversion, which directly illustrates that vibrational climbing is a coherent process. This experiment is a first exploration of the potential surface far from the harmonic region, one remarkable result being the good vibrational coherence observed even for highly excited vibrational states.
Generation and complete characterization of intense mid-infrared ultrashort pulses
C. Ventalon, J. M. Fraser, J.-P. Likforman, D. M. Villeneuve, P. B. Corkum, M. Joffre
J. Opt. Soc. Am. B 23, 332 (2006) PDF
Coherent vibrational climbing in carboxy-hemoglobin
C. Ventalon, J.M. Fraser, M.H. Vos, A. Alexandrou, J.-L. Martin, M. Joffre
Proc. Natl. Acad. Sc. (USA) 101, 13216 (2004) PDF
Time-domain interferometry for direct electric field reconstruction of mid-infrared femtosecond pulses
C. Ventalon, J.M. Fraser, M. Joffre
Opt. Lett. 28, 1826 (2003) PDF