Sum-frequency generation microscope for opaque and reflecting samples

We report on the performance of a microscope setup, which has been developed for the imaging of sum-frequency generation (SFG) from reflecting, nontransparent samples. In order to maximize the SFG intensity the sample has to be observed from one side at an angle near 60° with respect to the surface normal. The setup is designed (a) to keep focus over the full image field and (b) to compensate for the distortion of the field-of-view, both by means of a blazed grating. In contrast to “specular” SFG spectroscopy, the incident beams reflected from the sample and the generated SF light cannot be separated by angular filtering. In this setup the separation thus relies on spectral filtering only.