Atom Optics Using Microfabricated Structures

We present a novel method for fabricating precisely positioned small openings in thin silicon nitride membranes. Several optical elements for atoms have been constructed, including amplitude diffraction gratings and zone plates, and the results of experiments using these devices are presented. A method for creating a blazed diffraction grating is discussed. PACS: 35.10.-d, 42.25.-p Atom optics [1,2] refers to two things: a new point of view in which atoms in atomic beams are thought of and manipulated like photons in light beams, and a growing collection of techniques and devices for performing this manipulation. While some demonstrations of atom optics are over 20 years old including diffraction of atoms from crystal surfaces [3], single slit diffraction [4], and hexapole focusing lenses [5, 6] advances in laser and nanofabrication technology have lead to numerous recent demonstrations of various types of diffraction gratings [7-9] and zone plates [10, 11]. Other recent developments include the demonstration of atom mirrors using light and specially prepared surfaces [12, 13]. Recent theoretical developments suggest that momentum transfer by light offers several new possibilities for the construction of coherent beam splitters for atoms [14]. It now appears that the field of atom optics is developed well enough to allow the construction of devices containing several elements working together [15, 16]. This paper concerns optical elements for atoms made from thin membranes with precisely positioned openings for the atoms to pass through. These are essentially amplitude transmission devices the optical analog of holes cut in black paper. The short wavelength of atomic deBroglie waves demands sub-micron size holes, requiring the use of nanofabrication techniques. Although we have used both gold and silicon nitride nanofabricated devices, here we describe only techniques for the construction of the latter. Constmction of the gold gratings has been described elsewhere by its originators [17-20]. The first section of this paper describes details of the new fabrication process. The subsequent three sections discuss, in turn, the construction and performance of our atom diffraction gratings, a teclmique to employ electric fields to produce blazed diffraction gratings, and results from an imaging experiment using a zone plate. We conclude by offering several speculative comments about the future of atom optics using microfabricated structures.