The influence of phase-modulation on femtosecond time-resolved coherent Raman spectroscopy

It was shown recently that three scattering mechanisms with different time behaviours can be separated in timedomain CARS simply by varying the polarization of the detected anti-Stokes signal. In an extension of this work, the magic angle 49.1" for the elimination of the resonant-anisotropic contribution was verified experimentally. It was also found that the residual non-resonant scattering component observed at -60" with suppression of the common CARS interaction represents a six-wave mixing process involving the optical Kerr effect. Using the novel polarization techniques the vibrational dynamics of neat dimethyl sulphoxide was studied in the CH stretching region. Evidence is reported for homogeneous broadening of the symmetric mode at 2913 cm-' and for a doublet splitting of the asymmetric Raman band of the liquid at 2996 cm-' not resolved in spontaneous Raman spectros-COPY.

Femtosecond three‐colour CARS of liquids with magic polarization conditions

Purucker

Tunkin

Laubereau

1993

Non‐exponential dephasing of molecular vibrations in liquids, directly observed by ‘magic’ femtosecond CARS

Lindenberger

Rauscher

Purucker

et al. 1995

Using 'magic' polarization geometries in timeresolved coherent anti-Stokes Raman spectroscopy, the isotropic (purely vibrational) scattering contribution was investigated. Non-exponential dephasing was observed on the sub picosecond time-scale, described in the Anderson-Kubo formalism by the correlation time t, . Experimental data are reported for the neat liquids CH,BrCl and (CH,),SO in the CH stretching region. Values of t, = 330 fs and 240 fs, respectively indicate, homogeneous line broadening for the dephasing processes. The timedomain data are supported by a novel analysis of spontaneous Raman data.

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

Materny

Chen

Vierheilig

et al. 2001

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.