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We discuss the use of optical cavities as tools to search for dark matter (DM) composed of virialized ultra-light fields (VULFs). Such fields could lead to oscillating fundamental constants, resulting in oscillations of the length of rigid bodies. We propose searching for these effects via differential strain measurement of rigid and suspended-mirror cavities. We estimate that more than two orders of magnitude of unexplored phase space for VULF DM couplings can be probed at VULF Compton frequencies in the audible range of 0.1-10 kHz.

The solution phase n-doping of C 60 and PCBM with tetrabutylammonium fluoride is shown to occur via an initial chemical reaction followed by electron transfer to a second fullerene molecule. The formation of ionic and radical intermediate species has significant implications for the use of ionically functionalized materials as electron-selective interface layers in OPVs.The use of ionically functionalized polymers and molecules as electron-selective interfacial layers in organic photovoltaic cells (OPVs) has attracted signicant research interest in recent years. 1-5 Devices fabricated using these materials, such as ionically functionalized polyuorenes and fullerenes, have displayed power conversion efficiencies up to $9%, largely due to an increase in the cell open-circuit voltage (V oc ). 1-5 Despite these advances, the mechanism by which these materials affect device performance remains uncertain. 1-8 The observed increase in V oc is typically attributed to electrode work function reduction from preferential orientation of ionic pendant groups and associated counterions, resulting in a net dipole. 1-7 While it is likely that interfacial dipoles are present, the role of potential chemical reactions between the ionically functionalized material and active layer has received relatively little attention. 7,9,10 Recently, Li et al. reported unusually high conductivities (up to 3.2 S m À1 ) in PCBM/fulleropyrrolidinium iodide blend thin lms. 11 It was shown subsequently that lms deposited from solutions of tetrabutylammonium salts (TBAX: X ¼ F, Br, I, OH, AcO) and PCBM also resulted in highly conducting lms. 12 Based on solution phase studies using C 60 , it was postulated that direct electron transfer from anion (OH À or F À ) to fullerene results in the n-doped C 60 radical anion (C 60 _ À ) and donor radical (OH_ or F_). These studies suggest that redox reactions between the interfacial material anions and PCBM in the active layer results in interfacial n-doping which would have signi-cant effects on interfacial energetics and charge extraction. However, given the electrophilicity of the fullerene molecule and nucleophilicity of anions studied, particularly F À and OH À , 13 the possibility of chemical reactions is signicant in both solution and solid state. Based on this, as well as the large mismatch in standard reduction potentials between OH À /F À and C 60 , 14 we hypothesized that the reported observation of radical species resulted from an initial chemical reaction between the nucleophile and C 60 followed by electron transfer to a second C 60 molecule (Scheme 1). Similar reactions have been demonstrated previously in both solution and the solid state 15-18 Such reaction chemistry would result in the generation of numerous potential products. The understanding of such chemistry is essential for elucidation of a mechanistic description of interface energetics and charge extraction processes towards the rational design of highly efficient OPVs.UV-vis-NIR spectroscopy was used to monitor the reaction be...

A Mach-Zehnder interferometer (MZI) based fiberoptic refractive index (RI) sensor is constructed by uniformly tapering standard single mode fiber (SMF) for RI measurement. A custom flame-based tapering machine is used to fabricate microfiber MZI sensors directly from SMFs. The fabricated MZI device does not require any splicing of fibers and shows excellent RI sensitivity. The sensor with a cladding diameter of 35.5 µm and length of 20 mm exhibits RI sensitivity of 415 nm/RIU for RI range of 1.332 to 1.384, 1103 nm/RIU for RI range of 1.384 to 1.4204 and 4234 nm/RIU for RI range of 1.4204 to 1.4408, respectively. The sensor reveals a temperature sensitivity of 0.0097 nm/°C, which is relatively low in comparison to its ultra-high RI sensitivity. The proposed inexpensive and highly sensitive optical fiber RI sensors have numerous applications in chemical and biochemical sensing fields.

This paper proposes a hierarchical image-based visual servoing (IBVS) strategy for dynamic positioning of a fully actuated underwater vehicle. In the kinematic loop, the desired velocity is generated by a nonlinear model predictive controller, which optimizes a cost function of the predicted image trajectories under the constraints of visibility and velocity. A velocity reference model, representing the desired closed-loop vehicle dynamics, is integrated with an IBVS kinematic model to predict the future trajectories. In the dynamic velocity tracking loop, a neural-network-based model reference adaptive controller is designed to ensure the convergence of the velocity tracking error in the presence of uncertainties associated with vehicle dynamic parameters, water velocity, and thrust forces. Comparative simulations with different control and system configurations are performed to verify the effectiveness of the proposed scheme and to illustrate the influences of the prediction horizon, cost function, closed-loop vehicle dynamics, and predictive velocity reference model on the IBVS system performance.

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A statistically repeatable, hot-air optical turbulence generator, based on the forced mixing of two air flows with different temperatures, is described. Characterization results show that it is possible to generate any turbulence strength up to CN2 Dh approximately 6 x 10(-10) m1/3, allowing a ratio of beam diameter to Fried's parameter as large as D/r0 approximately 25 for one crossing through the turbulator or D/r0 approximately 38 for two crossings. The outer scale (L0 approximately 133 +/- 60 mm) is found to be compatible with the turbulator mixing chamber size (170 mm), and the inner scale (l0 approximately 7.6 +/- 3.8 mm) is compatible with the values in the literature for the free atmosphere. The temporal power spectrum analysis of the centroid of the focused image shows good agreement with Kolmogorov's theory. Therefore the device can be used with confidence to emulate realistic turbulence in a controlled manner. A calibrated CN2 profile, both in layer altitude and strength, is necessary for the testing of off-axis adaptive optics correction (multiconjugate adaptive optics). Testing was done to calibrate the CN2 profile using the slope detection and ranging technique. The first results, with only one layer, show the validity of the approach and indicate that a multiple-pass scheme is viable with a few modifications of the current setup.