Experimental demonstration of the coherent control of the molecular iodine vibrational dynamics by chirped femtosecond light pulses (original) (raw)
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Vibrational dynamics of excited electronic states of molecular iodine
The Journal of Chemical Physics, 2007
Femtosecond degenerate four-wave-mixing spectroscopy following an initial pump laser pulse was used to observe the wave packet dynamics in excited electronic states of gas phase iodine. The focus of the investigation was on the ion pair states belonging to the first tier dissociating into the two ions I − ͑ 1 S͒ +I + ͑ 3 P 2 ͒. By a proper choice of the wavelengths of the initial pump and degenerate four-wave-mixing pulses, we were able to observe the vibrational dynamics of the B 3 ⌸ u + state of molecular iodine as well as the ion pair states accessible from there by a one-photon transition. The method proves to be a valuable tool for exploring higher lying states that cannot be directly accessed from the ground state due to selection rule exclusion or unfavorable Franck-Condon overlap.
The role of pulse sequences in controlling ultrafast intramolecular dynamics with four-wave mixing
International Reviews in Physical Chemistry, 2000
This article seeks to provide a fundamental understanding of time-resolved four-wave mixing (FWM) processes based on a large body of experimental measurements on a model system consisting of isolated iodine molecules. The theoretical understandingis based primarily on a diagrammatic approach. Doublesided Feynman diagrams are used to classify and describe the coherent FWM processes involved in the signal obtained with each pulse sequence. DiOE erent pulse sequences of degenerate femtosecond pulses are shown to control the optical phenomena observed, that is transient grating, reverse-transient grating, photon echo and virtual photon echo. The experimental data reveal clear diOE erences between the nonlinear optical phenomena. We ® nd that the virtual photon echo sequencek " ® k # k $ is the most e cient for controllingthe observation of groundor excited-state dynamics. The strategy followed to make this assessment was to compare transients when the time delay between two of the three pulses set in or out of phase with the excited-state vibrational dynamics. We have obtained a signal from pulse sequences k " k # ® k $ for which FWM signal generation for this twoelectronic-level system is forbidden. This signal can be explained by the cascading of a ® rst-order polarization and a second-order process to generate the FWM signal. The implications of our ® ndings are discussed in the context of multiplepulse methods for the control of intramolecular dynamics. ‹ Permanent address: N.N. Semenov
Optical Response of Fluorescent Molecules Studied by Synthetic Femtosecond Laser Pulses
The Journal of Physical Chemistry Letters, 2012
The optical response of the fluorescent molecule IR144 in solution is probed by pairs of collinear pulses with intensity just above the linear dependence using two different pulse shaping methods. The first approach mimics a Michelson interferometer, while the second approach, known as multiple independent comb shaping (MICS), eliminates spectral interference. The comparison of interfering and noninterfering pulses reveals that linear interference between the pulses leads to the loss of experimental information at early delay times. In both cases, the delay between the pulses is controlled with attosecond resolution and the sample fluorescence and stimulated emission are monitored simultaneously. An out-of-phase behavior is observed for fluorescence and stimulated emission, with the fluorescence signal having a minimum at zero time delay. Experimental findings are modeled using a two-level system with relaxation that closely matches the phase difference between fluorescence and stimulated emission and the relative intensities of the measured effects.
The Journal of Physical Chemistry A, 1999
Experimental control and characterization of intramolecular dynamics are demonstrated with chirped femtosecond three-pulse four-wave mixing (FWM). The two-dimensional (spectrally dispersed and timeresolved) three-pulse FWM signal is shown to contain important information about the population and coherence of the electronic and vibrational states of the system. The experiments are carried out on gas-phase I 2 and the degenerate laser pulses are resonant with the X (ground) to B (excited) electronic transition. In the absence of laser chirp, control over population and coherence transfer is demonstrated by selecting specific pulse sequences. When chirped lasers are used to manipulate the optical phases of the pulses, the two-dimensional data demonstrate the transfer of coherence between the ground and excited states. Positive chirps are also shown to enhance the signal intensity, particularly for bluer wavelengths. A theoretical model based on the multilevel density matrix formalism in the perturbation limit is developed to simulate the data. The model takes into account two vibrational levels in the ground and the excited states, as well as different pulse sequences and laser chirp values. The analytical solution allows us to predict particular pulse sequences that control the final electronic state of the population. In a similar manner, the theory allows us to find critical chirp values that control the transfer of vibrational coherence between the two electronic states. Wave packet calculations are used to illustrate the process that leads to the observation of ground-state dynamics. All the calculations are found to be in excellent agreement with the experimental data. The ability to control population and coherence transfer in molecular systems is of great importance in the quest for controlling the outcome of laser-initiated chemical reactions.
Chemical Physics Letters, 1995
Solvent-induced electronic predissociation (X -~ B -~ als(31-1) state) of molecular iodine is discussed using a classical ensemble representation of Heisenberg's equations of motion. Excitation of the intermediate B state by an uRrafast pulse creates a coherent vibrational motion in this bound state. The localized solvent-induced coupling to the a state results in the spawning of dissociation products which occurs in bursts, twice per vibrational period. Equations of motion for both the electronic and nuclear degrees of freedom in each electronic state are derived from a quantum mechanical Hamiltonian. These equations are coupled whenever two electronic states are interacting. The formalism includes coupling to the surrounding classical solvent. Comparison with a pump-probe experiment is provided. 0009-2614/95/$09.50
Femtosecond temporal spectroscopy and direct inversion to the potential: Application to iodine
Chemical Physics Letters, 1990
The use of femtosecond lasers in probing molecular dynamics is usually thought to yield improved temporal resolution, at the expense of spectral information. Here, we report on the use of femtosecond temporal spectroscopy (FTS) to yield accurate spectral information (vibrational and rotational) and to invert directly to the potential energy curve. As an example, we present the FTS analysis, inversion to the potential, and confirmatory wave packet calculations for the B 3&+U state of molecular iodine.
Optical-heterodyne-detected induced phase modulation for the study of femtosecond molecular dynamics
The Journal of Chemical Physics, 1991
A new experimental technique for the study of ultrafast optical response of nonlinear materials, which detects nonrelaxational response in the media with high sensitivity, is introduced. Polarization-selective optical-heterodyne-detection scheme is applied to the measurement of the spectral shift of a probe pulse which is caused by induced phase modulation (IPM) brought about by a pump pulse. This technique, being sensitive to the high-frequency component of the nonlinear response, is especially applicable to the study of intermolecular dynamics in disordered media. The temporal responses of the optical Kerr effect in liquid carbon tetrachloride, benzene, and carbon disulfide are studied using this technique with femtosecond optical pulses. In the response of benzene, damped oscillations are clearly observed which are due to intermolecular vibrational motions of the molecules. The data obtained from benzene and carbon disulfide are analyzed using a Fourier-transform method. The resp...
Femtosecond time-resolved spectroscopy of elementary molecular dynamics
Naturwissenschaften, 2002
Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is applied in order to prepare and monitor laser-induced vibrational coherences (wave packets) of different samples mainly in its electronic ground state but also in excited states. The time evolution of these wave packets gives information on the dynamics of molecular vibrations. In a first example the femtosecond (fs) CARS transients of iodine are investigated. By changing the relative delay between the applied laser pulses of this non-degenerated four-wave mixing technique, both the wavepacket motion on the electronically excited and the ground states can be detected as oscillations in the coherent anti-Stokes signal. Second we report on selective excitation of the vibrational modes in the electronic ground state of polymers of diacetylene by means of a femtosecond time-resolved CARS scheme. This selectivity is achieved by varying the phase shape (chirp) and the relative delay between the exciting laser pulses.
Femtosecond pump-probe and four-wave mixing spectroscopies applied to simple molecules
Vibrational Spectroscopy, 1999
. A femtosecond three color pumprdump-probe scheme in combination with a time-of-flight TOF mass selective detection unit has been applied to study vibrational wave packet dynamics in the electronic ground state of cold K 2 molecules. A spectral analysis of the time domain signal reveals two different wave packet contributions: one from a stimulated Raman process and one from stimulated emission pumping. Also femtosecond time-resolved degenerate Ž . four-wave mixing DFWM spectroscopy is performed in order to investigate molecular dynamics in iodine molecules in the gas phase. Depending on the timing of the laser pulses different dynamics are reflected in the DFWM transient signal. By the use of time-evolution diagrams, the varying contribution of ground and excited state dynamics can be explained conclusively. q