We report coherent anti-Stokes Raman scattering (CARS) microscopy with ns-pulses. The chosen wide-field geometry allows imaging of the whole field of view at once, without scanning of the sample. Tuning the difference of the two incident laser frequencies overlapping at the sample to a specific vibrational level, one can map the spatial distribution of selected Raman active molecules. Both the CARS signal of the surrounding solvent can be excited (negative contrast) as well as the signal of the structure embedded by the solvent (positive contrast). As a biological sample we used slices of a sunflower seed and tuned to the vibrational transition of its ingredient - linoleic acid - at 2870 cm-1 which corresponds to the strongest C-H stretching vibration. Even with a single pair of laser pulses of 3 ns duration it was possible to acquire a rough, but still meaningful image.
We use coherent anti-Stokes Raman scattering (CARS) for functional imaging in microscopy. In contrast to other methods, excitation and detection are performed in a wide-field (non-confocal) setup, similar to a combination of dark field and epi-fluorescence microscopy. Thus, imaging of the whole sample is performed at once, i.e. without scanning, which promises the possibility of fast microscopy with vibrational contrast. The use of a nanosecond laser system rather
than typically used pico- or femtosecond systems facilitates a high spectroscopic resolution for various organic substances.