Sum frequency generation (SFG) allows the study of surfaces and inversion broken systems. In a new approach we implemented a wide field sum-frequency microscope combining the FHI infrared free electron laser (IR FEL) as excitation source with visible upconversion. The IR FEL provides a powerful, narrow band, and tunable light source [1]. By direct imaging of the SFG light with a microscope in a wide field scheme without scanning the sample or the focus [2], we achieve a spatial resolution well beyond the infrared diffraction limit.
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