Extended study of matter-wave diffraction from a periodic array of half-planes: Influences of van der Waals interactions on half-plane reflection/diffraction
Department of ChemistryHalf-plane reflection/diffraction refer to overall optical phenomena occurring at a periodic array of half-planes, playing a significant role in various fields of science and technology such as statistical quantum mechanics and ultrahigh frequency communication in urban areas. In Kirchhoff approximation, these phenomena are understood as multiple scatterings over half-planes. In atom optics, such reflection mechanism was utilized to increase reflectivity of atoms from solid materials and named as ???Fresnel diffraction mirror???.We recently have shown that matter-wave optical phenomena from square-wave gratings are governed by edge diffraction from an array of half-planes with decreasing strip widths of square-wave gratings while quantum reflection becomes predominant as the strip widths increase. Within this thesis, we extend our previous work to study how the interaction between matter-waves and top surfaces of strips affects half-plane reflection/diffraction. Interactions between particles and surfaces, namely, van der Waals interactions, influence matter-wave diffraction from square-wave gratings in two different manners - a manifestation of quantum reflection and a reduction of reflection/ diffraction efficiencies. To effectively study the latter case, i.e., an attenuation effect, we adapt a theoretical study obtained by Kouznetsov and Oberst. By comparing our measurement to the theoretical results, we find that the effects of van der Waals interactions appear differently for different particles, different grating periods and different de Broglie wavelengths. However, the adapted theoretical analysis is still not available to provide quantitative analysis for the attenuation effect. Hence, we suggest that the current theory should be improved by considering multiple scatterings of phase shifted waves induced by the van der Waals potentials in Fresnel integral. Furthermore, we look into the applicability of half-plane reflection/diffraction to van der Waals clusters and bigger molecules. Half-plane reflection of He3 was demonstrated in our previous paper with a square wave grating, and yet it remains to be challenging to study half-plane diffraction for the van der Waals clusters due to the low diffraction efficiencies. As a breakthrough, we suggest a new type of grating which is referred to as ???meta grating??? by embedding a large period into a periodic array of half-planes. Such a combination of two different grating periods is expected to enable enhanced diffraction efficiencies of fragile van der Waals clusters. Besides, a theoretical study is carried out with the consideration of attenuation effects for nitrogen and helium trimer to test the possibility of applying half-plane reflection/diffraction to bigger molecules. Considering that the reflectivity goes up with decreasing grating periods, square-wave gratings of 20 m period with 1 and 0.1 m strip widths are used in our calculation. Compared to quantum reflection, much higher reflectivity is observed and it shows the possibility to study matter-wave optical phenomena of particles with high polarizability.ope
