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The spectrum of Raman scattering contains information on the molecular structure and bonding configuration of the material and finds applications in materials characterization, microscopy, studies of chemical reactions and for the identification of molecular species. We study three novel approaches to increase the Raman signal that in general is very weak.
We study the coherent anti-Stokes Raman spectroscopy approach or FAST CARS with the production of maximal coherence states in the excited molecules. According to modern quantum optics theory, the cross section of the Raman scattering increases by many orders of magnitude when the maximal coherence between the states of the molecular vibronic transition is created. This can be achieved by shaping femtosecond laser pulses with a liquid-crystal phase modulator and by implementing a learning algorithm in the feedback loop that optimizes the measuring process for the maximal output signal. . For these studies we use a femtosecond laser system for the excitation and probing of fast molecular excitations.
We are implementing impulsive Raman spectroscopy to achieve selective molecular coherence by taking advantage of femtosecond pulse excitation and delayed probe observation.
In addition to fundamental spectroscopy aspects, one of the applied goals is the further development of optical means to detect bacterial and toxical antigens that can be airborn or be present on surfaces.
We investigate the origin of surface enhanced Raman scattering. Coupling of the incident light to the surface plasmon mode in a metal structure with inherently present spatial inhomogeneities (roughness) results in strong local enhancement of the electromagnetic field. Another interesting effect is connected to the charge transfer effect, where photo exited electrons at the metal surface resonantly interact with adsorbed molecules