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Ramanmikroskopie (FSRM)

Motivated by the advantages of stimulated over spontaneous Raman scattering in time resolved Raman spectroscopy we ventured into its application in spatially resolved Raman spectroscopy, that is in Raman microscopy. Raman microscopy offers chemically distinct signatures at the spatial resolution of light microscopy. As such it finds applications in material and polymer science as well as in biology and medicine. Since (spontaneous) Raman cross sections are small and thereby acquisition times long, huge efforts have been made to “speed up” Raman microscopy be means of non-linear interactions. Since the pioneering work of Xie et al. in 1999 emphasis has hereby been on coherent anti-Stokes Raman scattering. In a first proof of principle experiment we could prove that microscopy based on femtosecond stimulated Raman scattering is feasible and we decided to come up with a dedicated light source for this technique. The light source makes use of the large bandwidth of sub 10-fs lasers available commercially (see Figure). The pulses can directly serve as Raman probe replacing the white light continuum in (time resolved) FSRS. This eliminates an important source of noise, increases the repetition rate to 75 MHz, and decreases the peak power at the sample. Furthermore a femtosecond laser is more compact and more reliable than the femtosecond laser / amplifiers relied on in FSRS. The narrow bandwidth Raman pump is generated by amplifying the low frequency spectral wing of the laser in a fiber amplifier. Recording of Raman spectra with this set-up has been demonstrated. While recording such spectra a wavy background was observed. This background required an explanation and needed to be coped with. This has finally been achieved. Presently, we seek to improve the detector of the instruments and apply it in the polymer science and plant biology.