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The frequency-domain time-resolved four wave mixing spectroscopy technique is employed to study the vibrational coherence transfer taking place between the symmetric and asymmetric Co-stretching modes of rhodium(I) dicarbonyl acetylacetonate (RDC).The coherence transfer is shown to lead to different coherences with different frequencies.

Coherent multidimensional spectroscopy is performed in the mixed frequency/time domain, which has displayed both temporal and spectral quantum beating when two quantum states are simultaneously excited. The spectral quantum beating between the two degenerate asymmetric carbonyl stretch modes in a nickel tricarbonyl chelate is observed by using the nonrephasing, ground state bleaching coherence pathway in triply vibrationally enhanced four-wave mixing as the time delay between the first two excitation pulses changes.

A combination of frequency-domain two-color triply vibrational enhanced four-wave mixing and a time-resolved coherent transfer spectroscopy is employed to the nonradiative transition quantum states, wherein a superposition of quantum states evolves to a different superposition. The phenomenon of coherence transfer is found to provide an alternate pathway for studying the coupled quantum states in coherent multidimensional spectroscopy and hence can be used for several complex systems.

Triply vibrationally enhanced (TRIVE) four-wave mixing (FWM) spectroscopy in a mixed frequency/time domain experiment contains new output coherences that isolate nonlinear pathways that involve coherence transfer. The use of coherence transfer offers the opportunity for another form of coherent multidimensional spectroscopy where cross-peaks appear because of the coherence transfer between quantum states.

A mixed frequency/time domain ultrafast four wave mixing (FWM) approach provides similar capabilities, and also provides optical analogues of multiple- and zero-quantum heteronuclear nuclear magnetic resonance (NMR). The mixed frequency/time domain method allows the access of any set of quantum states with coherent multidimensional spectroscopy.

Erbium-doped barium titanate crystals studied by laser-induced florescence spectroscopy found thirteen spectroscopically distinct erbium ion sites. The relative concentrations of different sites changed as a function of the crystal and its preparation and treatment.

A report on a two-color frequency domain triply vibrationally enhanced (TRIVE) four-wave mixing (FWM) method that is fully resonant and provides coherent multidimensional vibrational spectra is presented. The findings indicate that TRIVE-FWM allows for the observation of the states and dephasing processes of the double vibrational coherences that are not accessible by traditional methods.

Triply vibrationally enhanced (TRIVE) four-wave mixing is a fully resonant, frequency domain spectroscopy that is capable of coherent multidimensional vibrational spectroscopy. It is experimentally shown that selection of the output frequency in two-color TRIVE methods constraints the selection rules that control the relative transition probabilities of their four transitions.

The intensity of the DOVE features themselves depends on the interference between the DOVE-Raman and the DOVE-IR coherence pathways. It is controlled by the time delay between the infrared pulses and the visible excitation pulse. It is demonstrated that background and CARS suppression and DOVE enhancement and suppression is achievable for 2D DOVE-FWM spectra using picosecond pulses.

Explores singly vibrationally enhanced infrared four wave mixing (SIVE-IRFWM) spectroscopy based on vibrational enhancements. Applicability of hyper-Raman scattering for SIVE-IRFWM rules; Application of the deutorobenzene Raman resonance changes to verify SIVE-IRFWM; Use of vibrational enhancement of SIVE to measure nuclear nonlinear polarization.

A diphenyloctatetraene (DPOT) doped bibenzyl crystal is a model system for studying the spectroscopic properties of polyenes because the well-defined local environment of the DPOT eliminates most of the inhomogeneous broadening that obscures many transitions. The spectra of the three DPOT sites in this host are measured with site-selective laser spectroscopy to define the vibrational, electronic, and vibronic states of the S0, S1, and S2 electronic states. Multiply resonant four-wave mixing spectra were then obtained using a coherent anti-Stokes Raman spectroscopy method (CARS) for a series of different laser frequencies in order to define the CARS excitation profile (CEP). The CEP profile of the C=C and C–C stretch vibrations showed strong enhancement of the four-wave mixing from the S2 state but only the C=C stretch mode had observable enhancement from the S1 state. Contrary to previous studies in pentacene, azulene, and perylene, DPOT did not exhibit enhancement of vibronic transitions that would permit mode selective or site-selective nonlinear spectroscopy. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Multiresonant coherent anti-Stokes Raman spectroscopy is performed with three tunable lasers on perylene doped polymethylmethacrylate (PMMA). Sharp vibronic features can be observed in vibronic scans at constant energy from the parent electronic transition when resonance is established within the inhomogeneously broadened electronic band. These features are attributed to the nonlinear line narrowing predicted by Ouellette and Denariez-Roberge for a higher order saturated coherent anti-Stokes Raman process since line narrowing should be absent for four wave mixing coherent anti-Stokes Raman spectroscopy. It is shown that the features are sharply dependent on the presence of a simultaneous vibrational resonance as is also predicted by the higher order coherent anti-Stokes Raman model. Excited state coherent anti-Stokes Raman spectroscopy with resonance enhancement from higher singlet states does not contribute to the narrow features since such a process would not have vibrational resonances. Conventional two laser coherent anti-Stokes Raman shows only a weak line at the vibronic transition. [ABSTRACT FROM AUTHOR]

Line narrowing of perylene vibronic transitions in poly(methylmethacrylate) (PMMA) samples has been demonstrated using multiply enhanced nonparametric spectroscopy. Three lasers are used to generate a four wave mixing signal that is resonantly enhanced by three simultaneous perylene resonances involving a vibrational state, a vibrationless excited electronic state, and a vibronic state of the excited electronic state. There is a correlation between the position of the electronic and vibronic states within the inhomogeneously broadened absorption spectrum. The correlation can be used to achieve line narrowing by fixing one of the resonances to a subset of perylene sites within the inhomogeneous profile so the other resonance of those sites will be selectively enhanced. The position of the line narrowed vibronic peaks depends upon the electronic detuning from the center of the inhomogeneously broadened absorption band as different sites within the band are probed. Excited state coherent processes involving resonance with higher singlet states are shown to be unimportant from the detuning dependence on a simultaneous vibrational enhancement. [ABSTRACT FROM AUTHOR]

Fully resonant, three laser, coherent Stokes Raman scattering (CSRS) is used to probe the vibrational correlations and couplings associated with the S0-S1 transition of azulene in a low temperature mixed molecular crystal. Unlike incoherent resonant emission, CSRS is not complicated by extra resonances due to relaxed emission. The spectra obtained confirm most of the assignments of the S1 vibronic fundamentals made by incoherent spectroscopies. In addition, however, the vibronic counterpart of the vibrational fundamental at 900 cm-1 is correlated to a previously unobserved vibronic resonance at 842.3 cm-1. Evidence of matrix moderated coupling, including possible site splitting and Fermi resonances involving lattice phonons, is given for the 677, 825, 917, 941, and 900 cm-1 vibrational levels. [ABSTRACT FROM AUTHOR]

Coherent, fully resonant four-wave mixing (FRFWM) spectroscopy is used to probe the vibrational and vibronic state of the pentacene S0 and S1 electronic states. High resolution is obtained using mixed molecular crystals at cryogenic temperatures. The FRFWM spectra combined with conventional absorption and fluorescence spectra allow correlation of the S1 fundamentals to the corresponding ground state normal coordinates. Couplings between modes are indicated and may be related to Fermi resonance of the pentacene vibrations by means of host librational phonons. [ABSTRACT FROM AUTHOR]

Pentacene doped benzoic acid crystals are used to study the line-narrowing capability of fully resonant four wave mixing for inhomogeneously broadened transitions. Both parametric and nonparametric nonlinear spectroscopies are used to scan the vibronic resonances of excited electronic states while maintaining resonance with a vibrational mode of the ground state and the vibrationless level of the excited state. The observed vibronic transitions correspond to modes that are coupled to the ground state mode. The spectra contain both lines that are narrowed and lines that have the full inhomogeneous width. Narrowing of the vibronic transitions is observed when site selection is performed on the vibrationless electronic transition in both parametric and nonparametric methods. Narrowing of the vibrational resonance is not observed under the same conditions showing that the vibrational and electronic inhomogeneous broadenings are not correlated. The shifts of the line positions and the changes in linewidths and relative intensities were measured across the inhomogeneous linewidth for both methods. The nonlinear signal intensity was also measured as a function of laser intensity. All of the results are consistent with a theoretical description where saturation effects are dominant. [ABSTRACT FROM AUTHOR]

The site distribution of the different charge compensated sites in singly doped samples of SrCl2:Eu3+ and doubly doped samples containing a second rare earth ion has been measured by site selective laser spectroscopy for a range of different dopant concentrations and annealing temperatures. The site distribution exhibits the same anomalous behavior as was observed in alkaline earth halide crystals as long as the dopant levels are not too low. At very low dopant levels, the anomalous behavior is not observed and the dependence follows that expected for simple mass action descriptions of defect equilibria. An association constant is obtained at the low concentrations and it is found that the amount of association is much less than would be expected from theoretical estimates based on Harwell automatic defect evaluation system (HADES) models. Extensive clustering is observed at lower concentrations than in the alkaline earth fluorides. The number of different clusters and the types of clusters do not appear to have a strong dependence on the ionic radius of the dopant ions as would be expected from HADES calculations. The anomalous site distributions at the higher concentrations are attributed to additional interactions between defect structures that result from strain interactions. Since these interactions lead to concentration dependence of the free energy of formation for the different defect sites, it will be necessary to include these effects in models that are used to predict the relative dominance of different sites. [ABSTRACT FROM AUTHOR]