Tight focal spots using azimuthally polarised light from a Fresnel cone

When focusing a light beam at high numerical aperture, the resulting electric field profile in the focal plane depends on the transverse polarisation profile, as interference between different parts of the beam needs to be taken into account. It is well known that radial polarised light produces a longitudinal polarisation component and can be focused below the conventional diffraction limit for homogeneously polarised light, and azimuthally polarised light that carries one unit of angular momentum can achieve even tighter focal spots. This is of interest for example for enhancing resolution in scanning microscopy. There are numerous ways to generate such polarisation structures, however, setups can be expensive and usually rely on birefringent components, hence prohibiting broadband operation. We have recently demonstrated a passive, low-cost technique using a simple glass cone (Fresnel cone) to generate beams with structured polarisation. We show here that the polarisation structure generated by Fresnel cones focuses better than radial polarised light at all numerical apertures. Furthermore, we investigate in detail the application of polarised light structures for two-photon microscopy. Specifically we demonstrate a method that allows us to generate the desired polarisation structure at the back aperture of the microscope by pre-compensating any detrimental phase shifts using a combination of waveplates

Comparison of beam generation techniques using a phase only spatial light modulator

Whether in art or for QR codes, images have proven to be both powerful and efficient carriers of information. Spatial light modulators allow an unprecedented level of control over the generation of optical fields by using digital holograms. There is no unique way of obtaining a desired light pattern however, leaving many competing methods for hologram generation. In this paper, we test six hologram generation techniques in the creation of a variety of modes as well as a photographic image: rating the methods according to obtained mode quality and power. All techniques compensate for a non-uniform mode profile of the input laser and incorporate amplitude scaling. We find that all methods perform well and stress the importance of appropriate spatial filtering. We expect these results to be of interest to those working in the contexts of microscopy, optical trapping or quantum image creation

What Limits the Rate Capability of Li-S Batteries during Discharge: Charge Transfer or Mass Transfer?

Li-S batteries exhibit poor rate capability under lean electrolyte conditions required for achieving high practical energy densities. In this contribution, we argue that the rate capability of commercially-viable Li-S batteries is mainly limited by mass transfer rather than charge transfer during discharge. We first present experimental evidence showing that the charge-transfer resistance of Li-S batteries and hence the cathode surface covered by Li2S are proportional to the state-of-charge (SoC) and not to the current, directly contradicting previous theories. We further demonstrate that the observed Li-S behaviors for different discharge rates are qualitatively captured by a zero-dimensional Li-S model with transport-limited reaction currents. This is the first Li-S model to also reproduce the characteristic overshoot in voltage at the beginning of charge, suggesting its cause is the increase in charge transfer resistance brought by Li2S precipitation

Strain induced electrochemical behaviors of ionic liquid electrolytes in an electrochemical double layer capacitor: Insights from molecular dynamics simulations.

Electrochemical Double Layer Capacitors (EDLCs) with ionic liquid electrolytes outperform conventional ones using aqueous and organic electrolytes in energy density and safety. However, understanding the electrochemical behaviors of ionic liquid electrolytes under compressive/tensile strain is essential for the design of flexible EDLCs as well as normal EDLCs, which are subject to external forces during assembly. Despite many experimental studies, the compression/stretching effects on the performance of ionic liquid EDLCs remain inconclusive and controversial. In addition, there is hardly any evidence of prior theoretical work done in this area, which makes the literature on this topic scarce. Herein, for the first time, we developed an atomistic model to study the processes underlying the electrochemical behaviors of ionic liquids in an EDLC under strain. Constant potential non-equilibrium molecular dynamics simulations are conducted for EMIM BF4 placed between two graphene walls as electrodes. Compared to zero strain, low compression of the EDLC resulted in compromised performance as the electrode charge density dropped by 29%, and the performance reduction deteriorated significantly with a further increase in compression. In contrast, stretching is found to enhance the performance by increasing the charge storage in the electrodes by 7%. The performance changes with compression and stretching are due to changes in the double-layer structure. In addition, an increase in the value of the applied potential during the application of strain leads to capacity retention with compression revealed by the newly performed simulations. [Abstract copyright: © 2023 Author(s). Published under an exclusive license by AIP Publishing.

Irreversible vs reversible capacity fade of lithium-sulfur batteries during cycling: the effects of precipitation and shuttle

Lithium-sulfur batteries could deliver significantly higher gravimetric energy density and lower cost than Li-ion batteries. Their mass adoption, however, depends on many factors, not least on attaining a predictive understanding of the mechanisms that determine their performance under realistic operational conditions, such as partial charge/discharge cycles. This work addresses a lack of such understanding by studying experimentally and theoretically the response to partial cycling. A lithium-sulfur model is used to analyze the mechanisms dictating the experimentally observed response to partial cycling. The zero-dimensional electrochemical model tracks the time evolution of sulfur species, accounting for two electrochemical reactions, one precipitation/dissolution reaction with nucleation, and shuttle, allowing direct access to the true cell state of charge. The experimentally observed voltage drift is predicted by the model as a result of the interplay between shuttle and the dissolution bottleneck. Other features are shown to be caused by capacity fade. We propose a model of irreversible sulfur loss associated with shuttle, such as caused by reactions on the anode. We find a reversible and an irreversible contribution to the observed capacity fade, and verify experimentally that the reversible component, caused by the dissolution bottleneck, can be recovered through slow charging. This model can be the basis for cycling parameters optimization, or for identifying degradation mechanisms relevant in applications. The model code is released as Supplementary material B

Comparison of beam generation techniques using a phase only spatial light modulator

Whether in art or for QR codes, images have proven to be both powerful and efficient carriers of information. Spatial light modulators allow an unprecedented level of control over the generation of optical fields by using digital holograms. There is no unique way of obtaining a desired light pattern however, leaving many competing methods for hologram generation. In this paper, we test six hologram generation techniques in the creation of a variety of modes as well as a photographic image: rating the methods according to obtained mode quality and power. All techniques compensate for a non-uniform mode profile of the input laser and incorporate amplitude scaling. We find that all methods perform well and stress the importance of appropriate spatial filtering. We expect these results to be of interest to those working in the contexts of microscopy, optical trapping or quantum image creation

Retrospective study: laser excision versus combined laser, cryosurgery and intralesional 5-fluorouracil in the treatment of equine sarcoids

Background Laser excision is used routinely in the treatment of sarcoids but may be ineffective in cases where complete excision cannot be achieved. A multimodal approach is warranted in these cases. 5-FU may improve the lethal effect of cryosurgery as an adjunct to laser excision. Objectives To compare two treatment protocols for equine sarcoids, laser excision alone versus a combination protocol of laser excision, cryosurgery and 5-FU chemotherapy. Factors associated with sarcoid recurrence are also investigated. Study design Retrospective case controlled study. Results Eighty-four horses with 168 histologically confirmed sarcoids were included, with a median follow-up time of 39 months (IQR 21–62 months). Sarcoid recurrence at the treated site was reported in 38% of cases and in 23% of any individual sarcoid. No significant difference was demonstrated between treatment categories in either rate of sarcoid recurrence (p = 0.45 for any treated horse, p = 0.63 for individual sarcoid) or time to sarcoid recurrence (p = 0.73). Sarcoid recurrence was higher in horses with a greater number of sarcoids (OR 1.2 (1.0–1.5), p = 0.03); when treatment had been received prior to admission (OR 7.6 (2.0–33), p = 0.004). Horses with urogenital sarcoids or >1 mixed sarcoid experienced more rapid recurrence (HR 3.6 (1.3–10), p = 0.02 and HR 9.9 (3.3–30), p < 0.001) and recurrence was less rapid following the treatment of a horse's first sarcoid (HR 0.3 (0.1–0.7), p = 0.009). Main limitations Significant differences in case populations in each treatment category. Treatment selection was neither blinded nor randomised and missing data and recall bias limit the study's power. Sarcoid recurrence was owner reported. Conclusions When assessing the likelihood of sarcoid recurrence, characteristics of both the individual patient and sarcoid phenotype must be considered carefully when selecting a specific treatment protocol

Cavity-enhanced frequency up-conversion in rubidium vapour

We report the first use of a ring cavity to both enhance the output power and dramatically narrow the linewidth (<1MHz) of blue light generated by four wave mixing in a rubidium vapour cell. We find that the high output power available in our cavity-free system leads to power broadening of the generated blue light linewidth. Our ring cavity removes this limitation, allowing high output power and narrow linewidth to be achieved concurrently. As the cavity blue light is widely tunable over the 85Rb 5S1/2F=3 → 6P3/2 transition, this narrow linewidth light would be suitable for second-stage laser cooling, which could be valuable for efficient 85Rb BEC production

Evaluating the use of Apo-neocarzinostatin as a cell penetrating protein.

Protein-ligand complex neocarzinostatin (NCS) is a small, thermostable protein-ligand complex that is able to deliver its ligand cargo into live mammalian cells where it induces DNA damage. Apo-NCS is able to functionally display complementarity determining regions loops, and has been hypothesised to act as a cell-penetrating protein, which would make it an ideal scaffold for cell targeting, and subsequent intracellular delivery of small-molecule drugs. In order to evaluate apo-NCS as a cell penetrating protein, we have evaluated the efficiency of its internalisation into live HeLa cells using matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry and fluorescence microscopy. Following incubation of cells with apo-NCS, we observed no evidence of internalisation