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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[1] On Mars, silica derived from chemical weathering could precipitate to coat rocks and particles. We suggest that rock coatings of secondary amorphous silica may account for a widespread Martian surface spectral unit previously modeled as andesite or weathered basalt. In a laboratory study, we investigated the effects of synthetic silica coatings on thermal infrared (TIR) spectroscopic measurements. Secondary amorphous silica is spectrally similar to silicate glass and clay spectra used in previous spectroscopic models. Silica coating and substrate spectra combine nonlinearly to produce a composite spectrum of a coated rock. Silica coatings <10 mm thick effectively mask the spectral contribution of a silicate substrate. Therefore, the capability of volumetrically small amounts of silica present as thin coatings on rocks should be considered when seeking explanations for spectral variability of Martian surface materials.

[1] To understand the aqueous history of Mars, it is critical to constrain the alteration mineralogy of the Martian surface. Previously published analyses of thermal infrared (l = 6-25 mm) remote sensing data of Mars suggest that dark regions have $15-20% clay minerals. However, near-infrared (l = 1-3 mm) spectral results generally do not identify widespread clay minerals. Thermal infrared detections of clays on Mars are difficult to interpret owing in part to the relative paucity of published spectral analyses of clay minerals and clay-bearing materials using similar spectra (thermal infrared emission spectra). In this study, we present an analysis of the thermal emission spectral features (l = $6-25 mm or 400-1650 cm À1 ) of a suite of clay mineral reference materials and clay-bearing rocks, linking their spectral features to the crystal chemical properties of the clays. On the basis of this context provided by the emission spectral analysis of clay minerals and clay-bearing rocks, we reconsider the evidence for clay minerals on Mars from Thermal Emission Spectrometer (TES) results. We propose that global-scale clay abundances determined from TES probably represent a geologically significant surface component, though they may actually correspond to poorly crystalline aluminosilicates with similar Si/O ratios to clay minerals (0.3-0.4), rather than well-crystalline clays. If clay minerals or clay-like materials on Mars are poorly crystalline and/or dessicated, they may be detectable in the thermal infrared, but not easily detected with near-infrared data sets.

Abstract. The Imager for Mars Pathfinder (IMP) windsock experiment measured wind speeds at three heights within 1.2 m of the Martian surface during Pathfinder landed operations. These wind data allowed direct measurement of near-surface wind profiles on Mars for the first time, including determination of aerodynamic roughness length and wind friction speeds. Winds were light during periods of windsock imaging, but data from the strongest breezes indicate aerodynamic roughness length of 3 cm at the landing site, with wind friction speeds reaching 1 m/s. Maximum wind friction speeds were about half of the threshold-of-motion friction speeds predicted for loose, fine-grained materials on smooth Martian terrain and about one third of the threshold-of-motion friction speeds predicted for the same size particles over terrain with aerodynamic roughness of 3 cm. Consistent with this, and suggesting that low wind speeds prevailed when the windsock array was not imaged and/or no particles were available for aeolian transport, no windrelated changes to the surface during mission operations have been recognized. The aerodynamic roughness length reported here implies that proposed deflation of fine particles around the landing site, or activation of duneforms seen by IMP and Sojourner, would require wind speeds >28 m/s at the Pathfinder top windsock height (or >31 m/s at the equivalent Viking wind sensor height of 1.6 m) and wind speeds >45 m/s above 10 m. These wind speeds would cause rock abrasion if a supply of durable particles were available for saltation. Previous analyses indicate that the Pathfinder landing site probably is rockier and rougher than many other plains units on Mars, so aerodynamic roughness length elsewhere probably is less than the 3-cm value reported for the Pathfinder site.

A force sensor based on three weakly coupled resonators with ultrahigh sensitivity, Sensors & Actuators: A. Physical (2015), http://dx.doi.org/10.1016/j.sna. 2015.05.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractA proof-of-concept force sensor based on three degree-of-freedom (DoF) weakly coupled resonators was fabricated using a silicon-on-insulator (SOI) process and electrically tested in 20µTorr vacuum. Compared to the conventional single resonator force sensor with frequency shift as output, by measuring the amplitude ratio of two of the three resonators, the measured force sensitivity of the 3DoF sensor was 4.9 × 10 6 /N, which was improved by two orders magnitude. A bias stiffness perturbation was applied to avoid mode aliasing effect and improve the linearity of the sensor. The noise floor of the amplitude ratio output of the sensor was theoretically analyzed for the first time, using the transfer function model of the 3DoF weakly coupled resonator system. It was shown based on measurement results that the output noise was mainly due to the thermalelectrical noise of the interface electronics. The output noise spectral density was measured, and agreed well with theoretical estimations. The noise floor of the force sensor output was estimated to be approximately 1.39nN for an assumed 10Hz bandwidth of the output signal, resulting in a dynamic range of 74.8dB.

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