Optical filter wavefront distortion: out-of-band to in-band predictions and the effect of the illumination source bandwidth.

The wavefront distortion (WFD) of a surface with an optical filter coating is ideally measured at the operating wavelength (λ) and angle of incidence (θ) of the filter. However, this is not always possible, requiring that the filter be measured at an out-of-band wavelength and angle (typically λ=633n m and θ=0∘). Since the transmitted wavefront error (TWE) and reflected wavefront error (RWE) can depend on the measurement wavelength and angle, an out-of-band measurement may not give an accurate characterization of the WFD. In this paper, we will show how to predict the wavefront error (WFE) of an optical filter at the in-band wavelength and angle from a WFE measurement at an out-of-band wavelength and different angle. This method uses (i) the theoretical phase properties of the optical coating, (ii) the measured filter thickness uniformity, and (iii) the substrate's WFE dependence versus the angle of incidence. Reasonably good agreement was achieved between the RWE measured directly at λ=1050n m (θ=45∘) and the predicted RWE based on an RWE measurement at λ=660n m (θ=0∘). It is also shown through a series of TWE measurements using a light emitting diode (LED) and laser light sources that, if the TWE of a narrow bandpass filter (e.g., an 11 nm bandwidth centered at λ=1050n m) is measured with a broadband LED source, the WFD can be dominated by the chromatic aberration of the wavefront measuring system-hence, a light source that has a bandwidth narrower than the optical filter bandwidth should be used.

Will I publish this abstract? Determining the characteristics of medical education oral abstracts linked to publication.

BACKGROUND: Prior studies have shown that most conference submissions fail to be published. Understanding factors that facilitate publication may be of benefit to authors. Using data from the Canadian Conference on Medical Education (CCME), our goal was to identify characteristics of conference submissions that predict the likelihood of publication with a specific focus on the utility of peer-review ratings. METHODS: Study characteristics (scholarship type, methodology, population, sites, institutions) from all oral abstracts from 2011-2015 and peer-review ratings for 2014-2015 were extracted by two raters. Publication data was obtained using online database searches. The impact of variables on publication success was analyzed using logistic regressions. RESULTS: In total, 953 oral abstracts were reviewed from 2011 to 2015. Overall, the publication rate was 30.5% (291/953). Of 531 abstracts with peer-review ratings, between 2014 and 2015, 162 (31%) were published. Of the nine analyzed variables, those associated with a greater odds of publication were: multiple vs. single institutions (odds ratio (OR) = 1.72), post-graduate research vs. others (OR=1.81) and peer-review ratings (OR=1.60). Factors with decreased odds of publication were curriculum development (OR=0.17) and innovation vs. others (OR=0.22). CONCLUSION: Similar to other studies, the publication rate of CCME presentations is low. However, peer ratings were predictive of publication success suggesting that ratings could be a useful form of feedback to authors.

CONTEXTE: Des études ont montré que la plupart des résumés soumis pour présentations orales ne sont pas ultérieurement publiés. Il pourrait être utile aux auteurs de comprendre les facteurs qui favorisent la publication. À l'aide de données provenant de la Conférence canadienne sur l'éducation médicale (CCÉM), notre objectif était d'identifier les caractéristiques des résumés permettant de prédire les chances de publication et en particulier l'utilité des cotes attribuées par les réviseurs. MÉTHODOLOGIE: Les caractéristiques des études (type de projet d'érudition, méthodologie, population, établissements, institutions) de tous les résumés de présentation orale soumis pour les conférences de 2011 à 2015 et les cotes attribuées par les réviseurs entre 2014 et 2015 ont été extraites par deux évaluateurs. On a obtenu des données de publication en faisant des recherches dans des bases de données en ligne. L'effet des variables sur le potentiel de publication a été examiné à l'aide de régressions logistiques. RÉSULTATS: Au total, 953 résumés ont été révisé des années 2011 à 2015. Le taux de publication était de 30.5% (291/953) en somme. Des 531 résumés ayant été évalués des pairs, entre 2014 et 2015, 162 (31 %) ont été publiés. Parmi les neuf variables analysées, celles qui ont été associées à un nombre élevé de chances de publication étaient les suivantes : projet multi-institutionnel par rapport à institution unique (risque relatif (RR) = 1,72), travaux de recherche post-graduée par rapport à d'autres types (RR = 1,81) et présence de cotes attribuées par les réviseurs (RR = 1,6). Les facteurs associés à des moindres chances de publication étaient les suivants : articles portant sur le développement de cursus (RR = 0,17) et les innovations, par rapport à d'autres (RR = 0,22). CONCLUSION: Comme ce fut le cas pour d'autres études, le taux de publication à la suite d'une présentation au CCME est faible. Cependant, les cotes attribuées par les réviseurs permettaient de prédire les chances de publication ce qui semble indiquer que les cotes pourraient constituer une forme de rétroaction utile aux auteurs.

Mechanistic Insight into the Limiting Factors of Graphene-Based Environmental Sensors.

Graphene has demonstrated great promise for technological use, yet control over material growth and understanding of how material imperfections affect the performance of devices are challenges that hamper the development of applications. In this work, we reveal new insight into the connections between the performance of the graphene devices as environmental sensors and the microscopic details of the interactions at the sensing surface. We monitor changes in the resistance of the chemical-vapor deposition grown graphene devices as exposed to different concentrations of ethanol. We perform thermal surface treatments after the devices are fabricated, use scanning probe microscopy to visualize their effects down to nanometer scale and correlate them with the measured performance of the device as an ethanol sensor. Our observations are compared to theoretical calculations of charge transfers between molecules and the graphene surface. We find that, although often overlooked, the surface cleanliness after device fabrication is responsible for the device performance and reliability. These results further our understanding of the mechanisms of sensing in graphene-based environmental sensors and pave the way to optimizing such devices, especially for their miniaturization, as with decreasing size of the active zone the potential role of contaminants will rise.

Plasmonic colours predicted by deep learning.

Picosecond laser pulses have been used as a surface colouring technique for noble metals, where the colours result from plasmonic resonances in the metallic nanoparticles created and redeposited on the surface by ablation and deposition processes. This technology provides two datasets which we use to train artificial neural networks, data from the experiment itself (laser parameters vs. colours) and data from the corresponding numerical simulations (geometric parameters vs. colours). We apply deep learning to predict the colour in both cases. We also propose a method for the solution of the inverse problem - wherein the geometric parameters and the laser parameters are predicted from colour - using an iterative multivariable inverse design method.

Passivation of Plasmonic Colors on Bulk Silver by Atomic Layer Deposition of Aluminum Oxide.

We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer deposition (ALD) of thin films of aluminum oxide. The colors are rendered by silver nanoparticles produced by laser ablation and redeposition on silver. We then apply a two-step approach to aluminum oxide conformal film formation via ALD. In the first step, a low-density film is deposited at low temperature to preserve and pin the silver nanoparticles. In the second step, a second denser film is deposited at a higher temperature to provide tarnish protection. This approach successfully protects the silver and plasmonic colors against tarnishing, humidity, and temperature, as demonstrated by aggressive exposure trials. The processing time associated with deposition of the conformal passivation layers meets industry requirements, and the approach is compatible with mass manufacturing.

Visible light driven plasmonic photochemistry on nano-textured silver.

Plasmon assisted generation of silver sulfate from dodecanethiol is demonstrated on a nano-textured silver substrate with a strong surface plasmon resonance in the visible range. The observed photo-physical processes are attributed to hot charge carriers that are generated from the excitation of surface plasmon resonances using 532 nm laser light. Excited charge carriers are responsible for cleaving the alkane chain, and for generating reactive oxygen species which rapidly photooxidize the exposed sulfur atoms. The ability to drive photochemical reactions with photon energies in the visible range rather than in the UV, on nano-textured silver surfaces, will enable researchers to study photochemical transformations for a wide variety of applications. The strong optical absorbance across the visible range, combined with the fact that the substrates can be fabricated over large areas, naturally makes them candidates for solar driven photochemical applications, and for large scale plasmonic reactors.

Laser-induced plasmonic colours on metals.

Plasmonic resonances in metallic nanoparticles have been used since antiquity to colour glasses. The use of metal nanostructures for surface colourization has attracted considerable interest following recent developments in plasmonics. However, current top-down colourization methods are not ideally suited to large-scale industrial applications. Here we use a bottom-up approach where picosecond laser pulses can produce a full palette of non-iridescent colours on silver, gold, copper and aluminium. We demonstrate the process on silver coins weighing up to 5 kg and bearing large topographic variations (∼1.5 cm). We find that colours are related to a single parameter, the total accumulated fluence, making the process suitable for high-throughput industrial applications. Statistical image analyses of laser-irradiated surfaces reveal various nanoparticle size distributions. Large-scale finite-difference time-domain computations based on these nanoparticle distributions reproduce trends seen in reflectance measurements, and demonstrate the key role of plasmonic resonances in colour formation.

Femtosecond laser induced surface swelling in poly-methyl methacrylate.

We show that surface swelling is the first step in the interaction of a single femtosecond laser pulse with PMMA. This is followed by perforation of the swollen structure and material ejection. The size of the swelling and the perforated hole increases with pulse energy. After certain energy the swelling disappears and the interaction is dominated by the ablated hole. This behaviour is independent of laser polarization. The threshold energy at which the hole size coincides with size of swelling is 1.5 times that of the threshold for surface swelling. 2D molecular dynamics simulations show surface swelling at low pulse energies along with void formation below the surface within the interaction region. Simulations show that at higher energies, the voids coalesce and grow, and the interaction is dominated by material ejection.