Resonance CARS spectroscopy on diacetylene single crystals

et al. 1998

J. Raman Spectrosc.

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Two‐photon‐resonance four‐wave mixing (TPR‐FWM) spectroscopy was examined for the study of the permanent electric dipole moments of molecular states. A TPR‐FWM process of the type ω4=ω1‐ω2+ω3 in a three‐state dipolar system was considered. The extraction of data for the difference in permanent dipole moments (Δμ) of states involved in TPR was analysed in the case of resonance TPR‐FWM. Resonance TPR‐FWM measurements were performed in a solution of the polydiacetylene poly‐4BCMU. © 1998 John Wiley & Sons, Ltd.

Section: Resultsmentioning

confidence: 70%

Two-photon-resonance four-wave mixing for the study of permanent molecular dipoles

Hadjichristov

Киров

et al. 1998

J. Raman Spectrosc.

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“…4(a). This resonance is related to the third term on the righthand side of Eqn (30) and originates from the 3LC. Its linewidth corresponds to the population decay rate Q  of the resonantly excited state.…”

Section: Symmetric Part Of the Fwms Lineshapementioning

confidence: 98%

Spectral lineshape analysis of four-wave mixing spectra and its application to quasi-zero-dimensional II-VI semiconductor crystallites

Bischof

Lermann

et al. 1999

J. Raman Spectrosc.

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Theoretical and experimental investigations are presented in order to analyze the lineshape of fourwave mixing spectra recorded by means of electronically resonant folded BOXCARS spectroscopy (special technique of CARS, coherent anti-Stokes Raman scattering). The theoretical framework presented is based on the quantum-mechanical expression of the non-linear third-order susceptibility. In order to obtain model equations those contributions of the third-order susceptibility which give rise to strong electronic resonance enhancement were exclusively used. The participation of two-photon resonances and the inhomogeneous broadening of the electronic transitions is taken into account. The theoretical background presented was applied to a semiconductor model system consisting of quasi-zero-dimensional CdS x Se 1−x nanocrystallites. The inhomogeneous broadening of this low-dimensional system is mainly caused by the size distribution of the nanocrystallites. The lineshapes of the experimentally obtained four-wave mixing spectra are well described within the theoretical framework and the homogeneous linewidth of the resonantly excited electronic state can be deduced.

“…The set-up for the pulsed solid-state CARS measurements has also been described elsewhere in detail. 25 The simultaneous use of two dye lasers enabled us to perform scans of the Stokes laser wavenumber Q S and also the pump wavenumber Q p . Therefore, resonance CARS spectroscopy was possible.…”

Section: Spectroscopy In the Wavenumber Domainmentioning

confidence: 99%

“…110,111 Defects also seem to be correlated with the observation of chromism in these substances. 19,21,25,51 The interactions between the molecules and their surroundings were taken into consideration by the introduction of the inhomogeneous broadening, which is characterized by the parameter . Defects directly result in changes of the monomer matrix, which can be regarded as solvent for the polymer chains.…”

Section: Application Of the Resonance Raman Theorymentioning

confidence: 99%

A review on linear and non‐linear resonance Raman spectroscopy of the conjugated system polydiacetylene

Chen

Vierheilig

et al. 2001

J Raman Spectroscopy

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We review resonance Raman investigations of the linear conjugated p-electron system of polydiacetylenes embedded in single-crystalline monomer matrices. Absorption, luminescence, resonance Raman and resonance CARS spectroscopy were used to investigate vibronic properties of the polymers. As an example, we discuss the theoretical model applied for the simulation of the resonance Raman line and excitation profiles obtained from the polymer chains in FBS, TS/FBS and TS6 diacetylene single crystals. The theory is based on a Franck-Condon model, which considers a chain length dependence. The electronic transition energies and matrix elements were calculated by means of an LCAO MO (linear combination of atomic orbitals molecular orbital) calculation in the Hückel approach. An interaction between ensemble and intramolecular properties due to defects can be shown. Besides the well known polymer absorption, the partially polymerized single crystals of the diacetylenes under investigation show blue-shifted absorption bands in sharply separated crystal areas. The spectroscopic investigations of this chromism revealed that most probably growth defects in f111g crystal growth sectors influence the side-group geometry of the polymer chains. Using femtosecond time-resolved CARS spectroscopy, the dynamics of the vibrational excitation in the electronic ground and excited states can be investigated. Here, we report the controlled selective excitation of the polymers. We used a CARS scheme where the difference of pump and Stokes laser wavelengths is chosen to achieve resonance with several chain modes of the polydiacetylenes. By varying the timing and the phases of the femtosecond laser pulses, the timing and the intensity of these modes can be strongly influenced.