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We demonstrate a novel electrowetting liquid combination using a room temperature ionic liquid (RTIL) and a nonpolar liquid, 1-phenyl-1-cyclohexene (PCH) suitable for focus-tunable 3-photon microscopy. We show that both liquids have over 90% transmission at 1300 nm over a 1.1 mm pathlength and an index of refraction contrast of 0.123. A lens using these liquids can be tuned from a contact angle of 133 to 48° with applied voltages of 0 and 60 V, respectively. Finally, a three-photon imaging system including an RTIL electrowetting lens was used to image a mouse brain slice. Axial scans taken with an electrowetting lens show excellent agreement with images acquired using a mechanically scanned objective.

 

The authors present an erratum to update the Acknowledgements section in their published article, [“Fabrication and characterization of a two-dimensional individually addressable electrowetting microlens array,”Opt. Express31,30550(2023)10.1364/OE.497992].

 

In-situ monitoring techniques of reverse osmosis (RO) desalination systems, particularly those with chemical sensing capabilities, can provide the means for better understanding important scaling mechanisms as well as early scaling detection. In this work, both calcium sulfate and calcium carbonate scaling on RO membranes were detected concurrently in real time using Raman spectroscopy to provide a unique chemical fingerprint. Two different sampling methodologies (manual and automated) were employed, and their performance was evaluated by comparing the Raman detection times to concurrent values of flux decline. The manual sampling strategy resulted in the detection of calcium sulfate and calcium carbonate at mean permeate flux declines of 13 ± 10 % and 22 ± 3 %, respectively. The automated sampling strategy provided better performance, with detection of calcium sulfate and calcium carbonate at mean flux declines of 8 ± 5 % and 4 ± 3 %, respectively. The increasedsensitivity and decreased variability of the automated sampling strategy provided valuable preliminary insights for the selection of optimized sampling strategies. The ability to identify the chemical composition of different scaling crystals including their polymorphs is an important step toward better understanding of the crystallization pathways of multi-component feed streams used in seawater and brackish water RO desalination. 

We demonstrate a two-dimensional, individually tunable electrowetting microlens array fabricated using standard microfabrication techniques. Each lens in our array has a large range of focal tunability from −1.7 mm to −∞ in the diverging regime, which we verify experimentally from 0 to 75 V for a device coated in Parylene C. Additionally, each lens can be actuated to within 1% of their steady-state value within 1.5 ms. To justify the use of our device in a phase-sensitive optical system, we measure the wavefront of a beam passing through the center of a single lens in our device over the actuation range and show that these devices have a surface quality comparable to static microlens arrays. The large range of tunability, fast response time, and excellent surface quality of these devices open the door to potential applications in compact optical imaging systems, transmissive wavefront shaping, and beam steering.

 

Electrowetting-based adaptive optics are of great interest for applications ranging from confocal microscopy to LIDAR, but the impact of low-frequency mechanical vibration on these devices remains to be studied. We present a simple theoretical model for predicting the resonance modes induced on the liquid interface in conjunction with a numerical simulation. We experimentally confirm the resonance frequencies by contact angle modulation. They are found to be in excellent agreement with the roots of the zero-order Bessel functions of the first kind. Next, we experimentally verify that external axial vibration of an electrowetting lens filled with density mismatched liquids (Δρ = 250 kg/m3) will exhibit observable Bessel modes on the liquid–liquid interface. An electrowetting lens filled with density matched liquids (Δρ = 4 kg/m3) is robust to external axial vibration and is shown to be useful in mitigating the effect of vibrations in an optical system. 

In this work we present a two-dimensional micro-scale array of individually addressable, focal length tunable, electrowetting lenses fabricated using standard microfabrication techniques. The compact, transmissive nature of these arrays opens the possibility for integration into miniature optical systems involving wavefront shaping and beam steering. 

We have demonstrated an electronically controlled laser, generating 50 nJ picosecond pulses at 760 nm. The gain-switched pulses at 1032 nm are amplified in Yb-fiber and frequency converted in photonic crystal fiber using four-wave mixing.

 

Direct monitoring techniques of fouling in membrane-based filtration processes can be implemented as part of an effort to reduce the negative effects of membrane fouling. In particular, monitoring techniques with chemical characterization capability are crucial for the formulation of effective fouling prevention and mitigation strategies. In the present work, Raman spectroscopy was applied as an in-situ monitoring technique for calcium carbonate scaling on commercial reverse osmosis membranes. The bench-scale Raman monitoring system allowed for a qualitative chemical assay of the scaled membrane surface at sequential downstream and upstream axial positions. The time evolution of the downstream and upstream calcium carbonate Raman signal was evaluated with respect to computed values of local concentration at the membrane surface, revealing a statistically significant dependence (p < 0.001). The real-time Raman data were bolstered by results of post-mortem analysis (scanning electron microscopy, gravimetric measurements, and laser interferometry). The employed technique was capable of detecting crystals with characteristic lengths <50 μm. Preliminary evidence of polymorph detection was also presented with recommendations for improvements in the technique. 

Imaging sub-diffraction dynamics of neural nanostructures involved in behaviors such as learning and memory in a freely moving animal is not possible with existing techniques. Here, we present a solution in the form of a two-photon (2P), fiber-coupled, stimulated emission depletion microscope and demonstrate its capabilities by acquiring super-resolution imaging of mammalian cells. A polarization-maintaining fiber is used to transport both the 2P excitation light (915 nm) and the donut-shaped depletion beam (592 nm), which is constructed by adding two temporally incoherent and orthogonally polarized Hermite–Gaussian fiber modes. The fiber output is insensitive to bending or temperature changes and is the first demonstration toward deep tissue super-resolution imaging in awake behaving animals.