We present a microfabricated optical cavity, which combines a very small mode volume with high finesse. In contrast to other micro-resonators, such as microspheres, the structure we have built gives atoms and molecules direct access to the high-intensity part of the field mode, enabling them to interact strongly with photons in the cavity for the purposes of detection and quantum-coherent manipulation. Light couples directly in and out of the resonator through an optical fiber, avoiding the need for sensitive coupling optics. This renders the cavity particularly attractive as a component of a lab-on-a-chip, and as a node in a quantum network. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2132066͔ High-finesse optical cavities are central to many techniques and devices in atomic physics, 1 optoelectronics, 2 chemistry, 3 and biosensing. 4 As well as selecting spectral and spatial distributions of the classical electromagnetic field, optical cavities make it possible to harness quantum effects for applications in quantum information science. 1,5 For example, it is possible to produce single photons on demand using atoms 6,7 or ions 8 inside a cavity and to create entanglement between those that share a cavity photon. 9-11 Similar ideas are being pursued with quantum dots. 12,13 Microscopic cavities are of particular interest 14 because small volume gives the photon a large field and because they offer the possibility of integration with micro-opto-electro-mechanical systems 15 and atom chips. [16][17][18] Here we present a simple and innovative method for fabricating microscopic, broadly-tuneable, high-finesse cavities. These have the significant new feature that their structure is open, giving an atom, molecule or quantum dot direct access to an antinode of the cavity mode. This structure is therefore ideally suited for detecting small numbers of particles, 19 and miniaturizing quantum devices based on strong dipole-cavity coupling.We have made high-finesse, open optical cavities that operate in length at a range of approximately 20-200 m. Each cavity is formed by a concave micro-mirror and the plane tip of an optical fiber, both coated for reflection, as illustrated in Fig. 1͑a͒. Arrays of concave mirrors are fabricated in silicon by wet-etching isotropically through circular apertures in a lithographic mask using a mixture of HF and HNO 3 in acetic acid. The etch bath in which the wafer is immersed undergoes continuous agitation during the etching process, resulting in an approximately spherical surface profile, as shown in Fig. 1͑b͒. The etch rate and the final morphology of the silicon surface are highly dependent on the agitation and on the concentration of each component in the etchant. 20 Precise control over these factors gives us repeatable surface profiles in the silicon with 6 nm rms roughness. In our first experiment, gold is sputtered onto an array of mirror templates to form a layer 100 nm thick with a surface roughness of 10 nm. The plane mirror of the cavity is a dielectric multilayer, w...

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Concave pyramids are created in the ͑100͒ surface of a silicon wafer by anisotropic etching in potassium hydroxide. High quality micromirrors are then formed by sputtering gold onto the smooth silicon ͑111͒ faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into micro-optoelectromechanical systems and atom chips. We have shown that structures of this shape can be used to laser-cool and hold atoms in a magneto-optical trap.

The Casimir interaction is omnipresent source of forces at small separations between bodies, which is difficult to change by varying external conditions. Here we show that graphene interacting with a metal can have the best known force contrast to the temperature and the Fermi level variations. In the distance range 50 − 300 nm the force is measurable and can vary a few times for graphene with a bandgap much larger than the temperature. In this distance range the main part of the force is due to the thermal fluctuations. We discuss also graphene on a dielectric membrane as a technologically robust configuration.

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We report on the integration of small-scale optical components into silicon wafers for use in atom chips. We present an on-chip fibre-optic atom detection scheme that can probe clouds with small atom numbers. The fibres can also be used to generate microscopic dipole traps. We describe our most recent results with optical microcavities and show that single-atom detection can be realised on an atom chip. The key components have been fabricated by etching directly into the atom chip silicon substrate.

We have fabricated curved optical micromirrors on silicon. We expect to be able to form open optical cavities between these mirrors and plane mirrors coated on the ends of optical fibres. The curved mirror templates have been prepared with less than 10 nm surface roughness by means of isotropic chemical etching. Two different methods are used for the fabrication of the mirrors: the first method uses a silicon oxide mask, while the second uses dry etching to form an indentation in the silicon surface that is opened out by wet isotropic etching. After coating the silicon substrate with gold, good quality mirrors are obtained with R ∼ 98% in the near infra-red. We find that a reflectivity of approximately 98% can be achieved by this method. Cavities formed from these mirrors will be useful for manipulating single atoms.

Abstract.A novel process for the fabrication of a microelectromechanical systems (MEMS) metallic component with features smaller than 10 µm and high thermal conductivity was investigated. These may be applied in new or improved microscale components, such as (micro-) heat exchangers. In the first stage of processing, equal channel angular pressing (ECAP) was employed to refine the grain size of commercial purity aluminium (Al-1050) to the ultra fine grain (UFG) material. Embossing was conducted using a micro silicon mould fabricated by deep reactive ion etching (DRIE). Both cold embossing and hot embossing were performed on the coarse-grained and UFG Al-1050. Cold embossing on the UFG Al-1050 led to a partially transferred pattern from the micro silicon mould and high failure rate of the mould. Hot embossing on the UFG Al-1050 provided a smooth embossed surface with fully transferred pattern and low failure rate of the mould, while hot embossing on the coarse-grained Al-1050 resulted in a rougher surface with shear bands.