München 2004 – scientific programme
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MO: Molekülphysik
MO 20: Schwingung und Rotation
MO 20.6: Talk
Friday, March 26, 2004, 12:15–12:30, HS 355
Four-wave mixing spectroscopy of the S1 state of all-trans-β-Carotene using ultrashort laser pulses — •Hrvoje Skenderović1,2, Thomas Hornung1,3 und Marcus Motzkus1,4 — 1Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching — 2Institute of Physics, Bijenička cesta 46, 10000 Zagreb, Croatia — 3Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge MA 02139-4307 — 4Philipps-Universität, D-35032 Marburg, Germany
Time-resolved degenerate four wave mixing (DFWM) and pump + DFWM with a temporal resolution of 16 fs is used to excite and probe the modes of the electronic ground state 11Ag−, (S0), and the lowest lying dipole forbidden excited electronic state 21Ag−, (S1), of all-trans-β-Carotene. In a first step, we performed resonant (center wavelength 490-507nm) and non resonant (560nm) DFWM spectroscopy to characterize the temporal dynamics of the S0 modes. The signal shows long time dynamics together with pronounced oscillations. The decay with a time constant of 6-8 ps corresponds to the well-known relaxation of S1-S0, while the oscillations are attributed to the high-frequency vibrational modes of the S0 state (1000 - 1500 cm−1).
When an additional pump pulse (485 nm) is introduced, population in the excited S1 state is generated by energy relaxation and its vibrational dynamics can be probed by the time-resolved DFWM (560 nm) probe. Fast oscillations are observed which correspond exclusively to high-frequency vibrations of the S1 state.