Enhanced elastic scattering of He-2 and He-3 from solids by multiple-edge diffraction

We report on a method of enhanced elastic and coherent reflection of He-4(2) and He-4(3) from a micro-structured solid surface under grazing incidence conditions. The van der Waals bound ground-state helium clusters exhibit fundamental quantum effects: He-4(2), characterized by a single ro-vibrational bound state of 10(-7) eV dissociation energy, is known to be a quantum halo state; and He-4(3) is the only electronic ground-state triatomic system possessing an Efimov state in addition to the ro-vibrational ground state. Classical methods to select and manipulate these clusters by interaction with a solid surface fail due to their exceedingly fragile bonds. Quantum reflection under grazing incidence conditions was demonstrated as a viable tool for elastic scattering from a solid surface but suffers from small reflection probabilities for typical conditions. Here we demonstrate that multiple-edge diffraction enables enhanced elastic scattering of the clusters from a solid. A dual-period reflection grating, where the strips consist of micro-structured edge arrays, shows an up to ten fold increased reflection probability as compared to its conventional counterpart where the strips are plane patches enabling quantum reflection of the clusters. The observed diffraction patterns of the clusters provide evidence of the coherent and elastic nature of scattering by multiple-edge diffraction

Experimental test of Babinet???s Principle in matter-wave diffraction

We report on an experimental test of Babinet's principle in quantum reflection of an atom beam from diffraction gratings. The He beam is reflected and diffracted from a square-wave grating at near grazing-incidence conditions. According to Babinet's principle the diffraction peak intensities (except for the specular-reflected beam) are expected to be identical for any pair of gratings of complementary geometry. We observe conditions where Babinet's principle holds and also where it fails. Our data indicate breakdown conditions when either the incident or a diffracted beam propagates close to the grating surface. At these conditions, the incident or the diffracted He beam is strongly affected by the dispersive interaction between the atoms and the grating surface. Babinet's principle is also found to break down, when the complementary grating pair shows a large asymmetry in the strip widths. For very small strip widths, edge diffraction from half planes becomes dominant, whereas for the complementary wide strips the atom-surface interactions leads to a strong reduction of all non-specular diffraction peak intensities

Non-destructive quantum reflection of helium dimers and trimers from a plane ruled grating

We report on the non-destructive scattering and diffraction of He, He2 and He3 from a plane ruled reflection grating. At grazing incidence the normal component of the particle's wave-vector is sufficiently small to allow for quantum reflection at the attractive Casimir-van der Waals particle-surface interaction potential. Quantum reflection occurs tens of nanometres in front of the surface, before the dimers and trimers reach the region where the surface-induced forces would inevitably cause the breakup of the fragile bonds. The reflected particles are identified via their mass-dependent diffraction angles and by mass spectrometry. The intensity distributions of the observed diffraction patterns are discussed in terms of the grating's blaze angle.close1

Matter-wave diffraction from a periodic array of half planes

We report on reflection and diffraction of beams of He and D2 from square-wave gratings of 400-µm period and strip widths ranging from 10 to 200 µm at grazing incidence conditions. In each case, we observe fully resolved matter-wave diffraction patterns including the specular reflection and diffracted beams up to the ??2nd diffraction order. With decreasing strip width the observed diffraction efficiencies exhibit a transformation from the known regime of quantum reflection from the grating strips to the regime of edge diffraction from a half-plane array. The latter is described by a single-parameter model developed previously to describe phenomena as diverse as quantum billiards, scattering of radio waves in urban areas, and reflection of matter-waves from microstructures. Our data provide experimental confirmation of the widespread model. Moreover, our results demonstrate that neither classical reflection nor quantum reflection is essential for reflective diffraction of matter-waves from a structured solid, but it can result exclusively from half-plane edge diffraction

Effect of atom-surface interaction on matter-wave diffraction from a periodic array of half planes

We have recently shown that diffraction of matter-wave from a square-wave grating of 400-µm period and 10-µm wide strips results mainly from scattering off a periodic array of parallel half-planes. This phenomenon is understood as multiple diffractions of waves at those half-planes. Here we study how the interaction of the matter-wave with the grating surface of a finite width affects the half-plane array diffraction. The interaction induces an additional phase shift along the path of the matter-wave, and, therefore, reduces the diffraction efficiency. The interaction effects appear differently for He and D2, for gratings of different period with the same strip width, and for He atoms of different de Broglie wavelengths. Moreover, we demonstrate the reflection of fragile He3 from a square wave grating via the half-plane array diffraction. In the future, by designing a super-periodic half-plane array with a small half-plane period and a large grating super-period, it will be possible to study diffraction of fragile van der Waals clusters such as He2 and He3. The combination of half-plane array and super-period grating will lead to diffraction at enhanced reflection probabilities as compared to previous experiments

Babinet's principle in atom optics

We investigate Babinet???s principle in quantum reflection of helium atoms from diffraction gratings. Helium atom beams are reflected and diffracted by square-wave gratings at grazing incidence angles of a few milliradians. According to Babinet???s principle the diffraction intensities are expected to be identical for a pair of complementary geometric gratings. We figure out both conditions where Babinet???s principle fails and where it holds. Our data for the two complementary gratings reveal that the conditions for its breakdown are where either incident or diffracted beams propagate close to the grating surface. The breakdown of Babinet???s principle is also prominent near Rayleigh conditions where a new spectral order emerges from the grating surface. At these conditions, the incident and diffracted helium beams are strongly affected by the dispersive interaction between the atoms and the grating surface. We therefore attribute the breakdown to atom-surface interactions and emerging beam resonances. Contrarily, the principle holds for the conditions where the effects of the atom-surface interaction and the emerging beam resonances are not significant

Scattering of matter waves from various optical reflection gratings under grazing incident conditions

Handy mirrors and gratings for atoms and molecules would open new frontiers in matter-wave optics with neutral particles. The realization of such components for atoms and molecules, however, has required sophisticated electromagnetic fields, nano-fabrication, or particle cooling, because of their inherently short wavelength and strong interaction with a surface. We demonstrate that reflective gratings designed for photons can work as a grating or a mirror for atoms and molecules of a thermal energy when used under grazing incidence conditions. The matter-waves of He atoms and D2 molecules are reflected from various gratings that are easily fabricated or commercially available. We find out the critical factors affecting diffraction peak widths and efficiencies. Our analyses imply that quantum and multiple-diffraction reflections occurring at the grazing incidence conditions are the underlying physics allowing optical square-wave and blazed gratings to function as a grating or a mirror for those particles