Reconstructing vibrational states in warm molecules using four-wave mixing with femtosecond laser pulses (original) (raw)
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Optical and Quantum Electronics, 1996
The influence of the transition from the excited state on the coherent transients of pump-probe measurements in a three-level system is discussed. A theoretical study related to a selective scheme of differential absorption pump-probe spectroscopy is performed in the framework of a full semiclassical description of the interaction of light and matter. It is demonstrated how the coherent part of the modified signal may be used for detection of the up-transition from the excited state. Annihilation processes characteristic of molecular aggregates at high pump intensities are taken into account.
The Journal of Chemical Physics, 2004
We report the use of spectrally resolved femtosecond two-color three-pulse photon echoes as a potentially powerful multidimensional technique for studying vibrational and electronic dynamics in complex molecules. The wavelengths of the pump and probe laser pulses are found to have a dramatic effect on the spectrum of the photon echo signal and can be chosen to select different sets of energy levels in the vibrational manifold, allowing a study of the dynamics and vibrational splitting in either the ground or the excited state. The technique is applied to studies of the dynamics of vibrational electronic states in the dye molecule Rhodamine 101 in methanol.
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
Journal of Optics B: Quantum and Semiclassical Optics, 2002
A pair of coherent femtosecond pulse excitations applied to a molecule with strong electron-phonon coupling creates a coherent superposition of a low momentum and a high momentum wavepacket in the vibrational states of both the excited state and the ground state of the coherent transition. As the excited state is accelerated further, interference between the high momentum ground state contribution and the low momentum excited state contribution causes a photon echo. This photon echo is a direct consequence of quantum interference between separate vibrational trajectories and can therefore provide experimental evidence of the non-classical properties of molecular vibrations.
Applied Physics B, 2000
This paper reviews results on wave packet dynamics investigated by means of femtosecond time-resolved four-wave-mixing (FWM) spectroscopy. First, it is shown that by making use of the various degrees of freedom which are offered by this technique information about molecular dynamics on different potential-energy surfaces can be accessed and separated from each other. By varying the timing, polarization, and wavelengths of the laser pulses as well as the wavelength of the detection window for the FWM signal, different dynamics are coherently excited and probed by the nonlinear spectroscopy. As a model system we use iodine in the gas phase. These techniques are then applied to more-complex molecules (gas phase: benzene, toluene, a binary mixture of benzene and toluene; solid state: polymers of diacetylene matrix-isolated in single crystals of monomer molecules). Here, ground-state dynamics are investigated first without any involvement of electronically excited states and then in electronic resonance to an absorption transition in the investigated molecules. Signal modulations result which are due to wave packet motion as well as polarization beats between modes in different molecules. Phase and intensity changes yield information about intramolecular vibrational energy redistribution, population decay (T 1 ), phase relaxation (T 2 ), and coherence times.
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.
Journal of Raman Spectroscopy, 2000
The roles of pulse sequence and pulse chirp were explored using femtosecond three-pulse four-wave mixing (FWM). The experiments were carried out on gas-phase I 2 and the degenerate laser pulses are resonant with the transition between the X ( 1 6 g Y ) ground and B ( 3 0u Y ) excited electronic states. Impulsive excitation leads to the observation of vibrational coherence in the ground and the excited states. Control over the observed population and vibrational coherence is achieved by using specific pulse sequences. Using chirped pulses results in changes in vibrational coherence. When the FWM signal is spectrally dispersed, the two-dimensional data (wavelength and time delay) provide important spectroscopic information about the intramolecular dynamics of both electronic states. This information is not typically available in time or spectrally integrated measurements. A theoretical foundation for these observations based on the density matrix formalism is briefly discussed.
Sequences for controlling laser excitation with femtosecond three-pulse four-wave mixing
Faraday Discussions, 1999
Three-pulse four-wave mixing (FWM) is used here to study and control laser excitation processes. For general laser excitation processes, after a molecule interacts resonantly with a laser pulse, the molecule has a probability of being in the ground or in the excited state. Control over this process depends on the phase and amplitude of the electric Ðelds that interact with the molecular system. Here we show how three-pulse FWM can be used to control the excitation of iodine molecules. Depending on the time delay between the Ðrst two pulses, the observed signal reÑects the dynamics of the ground or excited state. A theoretical formalism based on the density matrix formulation is presented and solved for a four-level system. Experiments are found to be in excellent agreement with the theory. The inÑuence of linear chirp on three-pulse FWM experiments is explored. Spectrally dispersed three-pulse FWM is found to be extremely useful for studying the e †ect of chirp on laser excitation of molecular systems. Experimental demonstrations of these e †ects are included.
Chemical Physics Letters, 2002
We propose three-pulse four-wave mixing (FWM) in cooled molecules for computation. Femtosecond amplitude and phase shaped pulses encode information into a coherent superposition of vibrational states. The coherent coupling between the quantum states and the consecutive interactions with shaped pulses is used as quantum logic gates to create the final superposition of states. The resulting coherent virtual or stimulated photon echo signal corresponds to a vector or a matrix output, respectively. Photon echo is the optical analog to spin echo where inhomogeneous decoherence is cancelled. The experimental setup required is discussed and preliminary results are presented. Ó (M. Dantus). 0009-2614/02/$ -see front matter Ó 2002 Published by Elsevier Science B.V. PII: S 0 0 0 9 -2 6 1 4 ( 0 1 ) 0 1 3 8 8 -4
Spectrally resolved two-colour three-pulse photon echo studies of vibrational dynamics of molecules
Physica B: Condensed Matter, 2003
Spectrally resolved two-colour three-pulse photon echoes (PE) have been investigated on a femtosecond time scale for Rhodamine B in Methanol. The time evolution of the spectra of the PE signals and their dependence on the wavelength of the excitation pulses are analysed. New spectral features are observed which differ from the spectral profile of the probe pulse and which decay with a range of time constants. The influence of vibrational-electronic coupling on the PE spectra is discussed. The vibrational relaxation times (80-200 fs), which depend on the levels selected in the vibrational manifold, and the optical dephasing time (B400 fs) can be determined directly from the spectrally resolved PE measurements. r