Chirped pulse excitation in condensed phases involving intramolecular modes. II. Absorption spectrum (original) (raw)
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Chemical Physics Letters, 2000
We have calculated the absorption spectrum of an intense chirped pulse exciting a solute molecule in a solvent. In general it depends on both the real and imaginary part of the susceptibility (a phase-dependent absorption in the nonstationary media). We have shown that the absorption spectrum directly re¯ects the time evolution of a vibrationally non-equilibrium population dierence in the ground and excited electronic states at the con®guration coordinate corresponding to instantaneous Franck±Condon transition, when measured using high-power and strongly chirped pulses. A method has been proposed for extracting this time evolution from the measured absorption spectrum. Ó
Solvent-Controlled Theory Analysis of Chirped Pulse Excitation of Molecules in Solutions
The Journal of Physical Chemistry B, 2001
A simple and physically clear approach to the interaction of intense chirped pulses with large molecules in solutions is developed: time-dependent rate equations for integral populations of electronic molecular states. For weak interaction, the time-dependent transition rates have a form of the Marcus electron-transfer rate. For larger interactions, the transition rates take into account the saturation effect similar to the transition rates in the solvent-controlled theory of electron-transfer reactions. The developed theory is a good approximation to a more sophisticated treatment (J. Chem. Phys. 1998, 109, 4523) which reproduces the effects observed in recent chirped pulse experiments.
Selective excitation of diatomic molecules by chirped laser pulses
The Journal of Chemical Physics, 2000
A new method for the selective excitation of diatomic molecules in single vibrational states on excited electronic potentials by two-photon absorption is proposed. The method implies the use of two chirped strong pulse lasers detuned from the optical transition to an intermediate electronic state. We show under what scenarios the method is successful on the time-energy scale in which the pulses operate. They involved a long-time ͑nanosecond͒ weak-field regime and a short-time ͑picosecond͒ strong-field regime. The adiabatic representation in terms of energy levels or in terms of light-induced potentials is used to interpret the physical mechanism of the excitation. The efficiency and robustness of the scheme are demonstrated by the excitation of the ground vibrational state of the 1 ⌺ g (4s) electronic potential of the Na 2 molecule.
The Journal of Chemical Physics, 2003
We study the dynamics of two-photon nonresonant electronic excitation of diatomic molecules driven by chirped pulses. While the majority of the experimental results address the role of the chirp for fixed pulse bandwidth, we analyze the possibility of selective excitation for fixed time, as a function of the pulse bandwidth, depending on the sign of the chirp. With strong picosecond pulses and positive chirp it is shown that the dynamics always prepare the molecule in the ground vibrational level of the excited electronic state. The robustness of the dynamics inherits the properties of an effective Landau-Zener crossing. For negative chirp the final state is very sensitive to the specific pulse bandwidth. The dynamics of the system follow a complex convoluted behavior, and the final state alternates between low vibrational levels of the excited electronic state and excited vibrational levels of the ground potential, which become increasingly more excited with increasing bandwidth. The final electronic populations follow a double-period oscillatory behavior. We present a model based on sequential independent crossings which correlates the long-oscillation period with changes in the final vibrational state selected. We show that the short-oscillation period is related with nonadiabatic effects that give rise to fast dynamic Rabi flipping between the electronic states, providing only information of the field-molecule effective coupling. Although the short-oscillation period partially masks the expected results of the final populations, we show that it is still possible to retrieve information from the long-oscillation period regarding the frequencies of the electronic potentials. In order to do so, or in order to control the outcome of the dynamics, it is necessary to perform experiments scanning very different pulse bandwidths, and we propose a possible experimental implementation. All the numerical results of the paper are calculated for a model of the Na 2 dimer.
Solvent Environment Revealed by Positively Chirped Pulses
The Journal of Physical Chemistry Letters, 2014
The spectroscopy of large organic molecules and biomolecules in solution has been investigated using various time-resolved and frequency-resolved techniques. Of particular interest is the early response of the molecule and the solvent, which is difficult to study due to the ambiguity in assigning and differentiating inter-and intramolecular contributions to the electronic and vibrational populations and coherence. Our measurements compare the yield of fluorescence and stimulated emission for two laser dyes IR144 and IR125 as a function of chirp. While negatively chirped pulses are insensitive to solvent viscosity, positively chirped pulses are found to be uniquely sensitive probes of solvent viscosity. The fluorescence maximum for IR125 is observed near transform-limited pulses; however, for IR144, it is observed for positively chirped pulses once the pulses have been stretched to hundreds of femtoseconds. We conclude that chirped pulse spectroscopy is a simple one-beam method that is sensitive to early solvation dynamics.
Chirp effects on impulsive vibrational spectroscopy: a multimode perspective
Physical Chemistry Chemical Physics, 2010
The well-documented propensity of negatively-chirped pulses to enhance resonant impulsive Raman scattering has been rationalized in terms of a one pulse pump-dump sequence which ''follows'' the evolution of the excited molecules and dumps them back at highly displaced configurations. The aim of this study was to extend the understanding of this effect to molecules with many displaced vibrational modes in the presence of condensed surroundings. In particular, to define an optimally chirped pulse, to investigate what exactly it ''follows'' and to discover how this depends on the molecule under study. To this end, linear chirp effects on vibrational coherences in poly-atomics are investigated experimentally and theoretically. Chirped pump-impulsive probe experiments are reported for Sulforhodamine-B (''Kiton Red''), Betaine-30 and Oxazine-1 in ethanol solutions with o10 fs resolution. Numerical simulations, including numerous displaced modes and electronic dephasing, are conducted to reproduce experimental results. Through semi-quantitative reproduction of experimental results in all three systems we show that the effect of group velocity dispersion (GVD) on the buildup of ground state wave-packets depends on the pulse spectrum, on the displacements of vibrational modes upon excitation, on the detuning of the excitation pulses from resonance, and on electronic dephasing rates. Akin to scenarios described for frequency-domain resonance Raman, within the small-displacement regime each mode responds to excitation chirp independently and the optimal GVD is mode-specific. Highly-displaced modes entangle the dynamics of excitation in different modes, requiring a multi-dimensional description of the response. Rapid photochemistry and ultrafast electronic dephasing narrow the window of opportunity for coherent manipulations, leading to a reduced and similar optimal chirp for different modes. Finally, non-intuitive coherent aspects of chirp ''following'' are predicted in the small-displacement and slow-dephasing regime, which remain to be observed in experiment.
Pump-Probe Spectroscopy of Population Wave Packets with Intense Chirped Pulses
Israel Journal of Chemistry, 2004
We have studied the time evolution of population wave packets under intense chirped pulse excitation by resonance heterodyne optical Kerr effect spectroscopy. In general, this method enables us to obtain complementary information about population wave packets versus the absorption spectrum of an intense chirped pulse. We have generalized the "moving potentials" picture of one of the authors to a non-Debye solvent. We analyze the effects of both the parameters of the solventsolute system and the electric field on the signal of the heterodyne optical Kerr effect experiment.
Effects of chirp on two-dimensional Fourier transform electronic spectra
Optics Express, 2010
We examine the effect that pulse chirp has on the shape of twodimensional electronic spectra through calculations and experiments. For the calculations we use a model two electronic level system with a solvent interaction represented by a simple Gaussian correlation function and compare the resulting spectra to experiments carried out on an organic dye molecule (Rhodamine 800). Both calculations and experiments show that distortions due to chirp are most significant when the pulses used in the experiment have different amounts of chirp, introducing peak shape asymmetry that could be interpreted as spectrally dependent relaxation. When all pulses have similar chirp the distortions are reduced but still affect the anti-diagonal symmetry of the peak shapes and introduce negative features that could be interpreted as excited state absorption.
Weakly chirped pulses in frequency resolved coherent spectroscopy
The Journal of Chemical Physics, 2010
The role of weakly chirped pulses ͑time bandwidth product, ⌬⌬ Ͻ 0.61͒ on three-pulse photon echo signals has been systematically studied. Pulses with varying chirp were characterized with frequency resolved optical gating ͑FROG͒ and used to measure spectrally resolved three-pulse photon echoes of a dye in solution. The weakly chirped pulses give rise to markedly different echo signals for population times below ϳ100 fs. The chirped pulses can decrease or enhance spectral signatures of an excited state absorption transition in the echo signal. Furthermore, the observed dephasing dynamics depend on the phase of the electric fields. Simulations based on a three-level model and the electric fields retrieved from the FROG traces give a good agreement for photon echo experiments with both transform limited and chirped pulses. The simulations also allow for a numerical investigation of effects of chirp in two-dimensional spectroscopy. For a two-level system, the chirped pulses result in nonelliptical two-dimensional spectra that can erroneously be interpreted as spectral heterogeneity with frequency dependent dephasing dynamics. Furthermore, chirped pulses can give rise to "false" cross peaks when strong vibrational modes are involved in the system-bath interaction.
New Journal of Physics, 2008
Time-resolved spectrum after ultrashort pulse excitation revealed fine structure of instantaneous vibronic absorption spectra in a thiophene derivative. The probe photon energy-dependent amplitudes of molecular vibration coupled to the induced absorption were composed of several peaks. An absorbance-change peak-tracking method revealed four vibronic transitions buried in the time-integrated spectra over several vibrational periods of typical molecular vibration. Four vibronic transitions located at 2.024, 1.921, 1.818 and 1.731 eV were found to be correlated among themselves with respect to the photon energies and intensities of the peaks in the difference absorbance change spectra. From the size and sign of the correlation strengths the mechanism of the vibronic coupling was related to non-Condon mechanism and Herzberg-Teller vibronic coupling.