Universal Diffraction of Atomic and Molecular Matter-Waves: A Comparison of He and D2 Quantum Reflected from a Grating

Molecular beams of He and D-2 are scattered from a ruled diffraction grating in conical-mount geometry under grazing-incidence conditions. Fully resolved diffraction patterns as a function of detection angle are recorded for different grating azimuth angles and for two different kinetic energies of the particle beams. Variations in diffraction peak widths are traced back to different velocity spreads of He and D-2 determined by time-of-flight measurements. A comprehensive analysis of diffraction intensities confirms universal diffraction, that is, for identical deBroglie wavelengths, the relative diffraction intensities for He and D-2 are the same. Universal diffraction results from peculiarities of quantum reflection of the atoms and molecules from the diffraction grating. In quantum reflection particles scatter many nanometers in front of the surface from the long-range attractive branch of the particle-surface interaction potential without probing the potential well and the short-range repulsive branch of the potential.