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In the Poisson-spot experiment, waves emanating from a source are blocked by a circular obstacle. Due to their positive on-axis interference an image of the source ͑the Poisson spot͒ is observed within the geometrical shadow of the obstacle. In this paper we report the observation of Poisson's spot using a beam of neutral deuterium molecules. The wavelength independence and the weak constraints on angular alignment and position of the circular obstacle make Poisson's spot a promising candidate for applications ranging from the study of large molecule diffraction to patterning with molecules. DOI: 10.1103/PhysRevA.79.053823 PACS number͑s͒: 37.20.ϩj, 03.75.Ϫb, 37.25.ϩk Diffraction experiments played a crucial role in establishing the existence of de Broglie matter waves ͓1-3͔. Today, matter-wave diffraction is used, among other applications, to investigate quantum interference of large molecules ͓4͔, enabling the study of quantum decoherence ͓5͔ and its role in the quantum-to-macroscopic-world transition. These experiments have mostly been carried out with free-standing material gratings ͓6,7͔ or light wave gratings ͓8͔. The largest molecules so far ͑Ͼ3 nm͒ for which quantum interference was successfully demonstrated were perfluoroalkylfunctionalized azobenzenes in a Kapitza-Dirac-Talbot-Lau interferometer ͓9͔. Scaling such experiments to even larger objects, such as macromolecules or perhaps even viruses, is a tantalizing prospect. In principle, this should be possible to some degree with a Kapitza-Dirac-Talbot-Lau interferometer. However, as the size of the molecule and/or object approaches the distance between grating bars difficulties arise. In the case of material gratings, van der Waals ͑vdW͒ forces increasingly limit interference contrast by adding a locally varying coherent phase shift. In fact, even blocking may occur. In the case of light gratings spontaneous emission and photon absorption are likely to perturb coherence. Furthermore, for the Talbot-Lau configuration the distance between the three gratings is a function of wavelength, and thus requires wavelength selection. This limits effective intensity of the commonly used thermal sources because only a fraction of the emitted molecules can be used in the experiment. In the case of clusters, the necessity of mass selection constrains effective source intensity additionally. Finally, alignment of the gratings, both with respect to each other and the vertical, is challenging, and misalignment can cause classical Moiré fringes which differ from expected interference patterns only in visibility and wavelength dependence.In this paper we make use of the Poisson-spot configuration to demonstrate quantum interference in a beam of molecules. The Poisson spot refers to a classical-optics experiment, in which a point light-source is blocked by a circular obstacle. Wave theory predicts that the intensity on the optical axis within the geometrical shadow is the same as without the blocking obstacle due to the cylindrical symmetry ͓11͔, resulting in a bright i...

An immersion scheme is used to improve resolution, exposure latitude, and depth-of-focus in zone-plate-array lithography ͑ZPAL͒. We believe this is the first implementation of an immersion scheme in a maskless lithography system. Replacing air with de-ionized water as the medium between the zone-plate array and the substrate effectively increases the system's numerical aperture and consequently, enhances its patterning capabilities. The design and fabrication process of an immersion zone plate is described. Its behavior is then characterized through the experimental reconstruction of its point-spread function, and compared to the theoretical model. A wide variety of patterns were printed, demonstrating the improved lithographic performance of immersion ZPAL.

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