Bragg diffraction of large organic molecules

We demonstrate Bragg diffraction of the antibiotic ciprofloxacin and the dye molecule phthalocyanine at a thick optical grating. The observed patterns show a single dominant diffraction order with the expected dependence on the incidence angle as well as oscillating population transfer between the undiffracted and diffracted beams. We achieve an equal-amplitude splitting of $14 hbar k$ (photon momenta) and maximum momentum transfer of $18 hbar k$. This paves the way for efficient, large-momentum beam splitters and mirrors for hot and complex molecules.