engleski

Four-wave mixing spectroscopy of the S1 state of all trans ß-Carotene using ultrashort laser pulses

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 11Ag-, (S0), and the lowest lying dipole forbidden excited electronic state 2 1Ag-, (S1), of all trans-ß-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 of 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.

Time-resolved degenerate four wave mixing

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