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To overcome the inefficiency in household energy use, energy labels with a grade-like categorical efficiency rating-scale are widely used across the globe. However, presenting energy efficiency information in categories has been found to induce heuristic rather than rational decision-making, known as the "class valuation effect": consumers value the classes, while being inattentive to the actual energy use of the respective appliance. Although replacing the categorical by a continuous scale could eradicate this effect, it has not been formally examined to what extent a continuous scale promotes more rational decision-making. This study investigates whether visualising energy efficiency using a continuous-scale instead of a categorical-scale energy label increases consumers’ awareness of the energy performance of appliances. We experimentally examine this question in an online survey with randomised decision tasks conducted in China and the Netherlands, two countries using energy labels with categorical rating-scale whose populations differ in cognitive style and energy literacy (energy-related knowledge, attitudes, and behaviours). We find that continuous-scale labels are overall more effective in promoting rational decision-making. For Dutch respondents the effectiveness depends on their holistic cognitive tendency and the type of comparison they are faced with, whereas the Chinese sample is not sensitive to these moderators. Moreover, we find that the different aspects of energy literacy have opposing influence on rational choices: possessing knowledge related to daily-life energy use increases the likelihood of rational decisions, while energy-saving attitudes and behaviours encourage individuals to opt for more energy-efficient appliances even when it is not economically optimal. Based on the results, we suggest to represent energy efficiency on continuous scales as an auxiliary visual information to support purchase decisions. In energy education and information programmes, emphasis should be put on energy knowledge that directly links to daily life, which is well translated into consumers’ conscious decisions.

We investigate laser ablation of crystalline silicon induced by a femtosecond optical vortex beam, addressing how beam properties can be obtained by analyzing the ablation crater. The morphology of the surface structures formed in the annular crater surface allows direct visualization of the beam polarization, while analysis of the crater size provides beam spot parameters. We also determine the diverse threshold fluences for the formation of various complex microstructures generated within the annular laser spot on the silicon sample. Our analysis indicates an incubation behavior of the threshold fluence as a function of the number of laser pulses, independent of the optical vortex polarization, in weak focusing conditions.

We report an experimental analysis of femtosecond laser induced surface structuring of silicon by exploiting both Gaussian and Optical Vortex beams. In particular, we show how different surface patterns, consisting of quasi-periodic ripples and grooves, can be obtained by using different states of polarization offered by optical vortex beams. Both for Gaussian and optical vortex beams, an increase of the number of laser pulses, N, or beam energy, E-0, leads to a progressive predominance of the grooves coverage, with ripples confined in specific regions of the irradiated area at lower fluence. The average period of ripples and grooves shows a different dependence as a function of both E-0 and N, underlying important differences in mechanisms leading to the formation of ripples and grooves. In particular, our experimental characterization allows identifying a preliminary stage of grooves generation with rudimental surface structures, preferentially directed parallel to the laser polarization. This supports the idea that one possible mechanism of grooves formation lies in the progressive aggregation of clusters of nanopartides densely decorating the ripples. Our experimental findings provide important indications on the basic understanding of the processes involved in laser surface structuring with ultrashort pulses that can guide the design of the surface patterns. (C) 2016 Elsevier B.V. All rights reserved.

We report a detailed theoretical and experimental analysis of the surface structures induced by ultrashort laser pulses on silicon. We address two issues seldom considered in the literature: i) bending and bifurcation of surface ripples and ii) the mechanism of microgrooves formation. Our experimental results illustrate the diverse morphological features of surface structures, which are explained by taking into account the variation of the dielectric constant of the target surface at different excitation levels, by means of a theoretical approach based on the combination of two-temperature model, free-carrier dynamics and Sipe model. In particular, calculated spatial distributions of the deposited laser energy on the target surface provide direct evidence of the diverse morphological characteristics of the produced structures, eventually explaining ripples bending and bifurcation phenomena, as well as grooves formation. The good agreement between model predictions and experimental findings suggests that the proposed approach ascertains the main physical mechanisms underlying both ripples and grooves formation, and influencing their fine morphological features. In addition to providing a deeper understanding of the mechanisms involved in femtosecond direct laser surface processing, our results highlight interesting ways of implementing the design of surface structures of applicative interest.

Irradiation of crystalline silicon with femtosecond laser pulses produces a variety of quasi-periodic surface structures, among which sub-wavelength ripples creation is largely studied. Here we report an experimental investigation and a theoretical interpretation focusing on the seldom considered issue of quasi-periodic, micron spaced grooves formation. We characterize the morphological evolution of the grooves generation and experimentally single out the variation of the threshold fluence for their formation with the number of pulses N, while typical ripples simultaneously produced in the irradiated area are always considered for comparison. Our experimental findings evidence a power law dependence of the threshold fluence on the number of pulses both for ripples and grooves formation, typical of an incubation behavior. The incubation factor and single pulse threshold are (0.76 ± 0.04) and (0.20 ± 0.04) J/cmsup2/supfor ripples and (0.84 ± 0.03) and (0.54 ± 0.08) J/cmsup2/supfor grooves, respectively. Surface-scattered wave theory, which allows modeling irradiation with a single pulse on a rough surface, is exploited to interpret the observed structural modification of the surface textures. A simple, empirical scaling approach is proposed associating the surface structures generated in multiple-pulse experiments with the predictions of the surface-scattered wave theory, at laser fluencies around the grooves formation threshold. This, in turn, allows proposing a physical mechanism interpreting the grooves generation as well as the coexistence and relative prominence of grooves and ripples in the irradiated area.

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate. The different states of an optical vortex beam carrying an orbital angular momentum ℓ = ±1 are used to demonstrate the fabrication of various regular surface patterns on silicon. The spatial features of the regular rippled and grooved surface structures are correlated with the state of polarization of the optical vortex beam. Moreover, scattered surface wave theory approach is used to rationalize the dependence of the surface structures on the local state of the laser beam characteristics (polarization and fluence). The present approach can be further extended to fabricate even more complex and unconventional surface structures by exploiting the possibilities offered by femtosecond optical vector fields.

We report an experimental investigation on the irradiation of copper thin films with high repetition rate femtosecond laser pulses (1040 nm, 50 MHz), in ambient air and liquid water. We observe a novel, striking phenomenon of chromatic copper oxides (cupric oxide and cuprous oxide) annuli generation. The characteristic features of the chromatic copper oxide annuli are studied by exploiting micro-Raman Spectroscopy, Optical and Scanning Electron Microscopies. In the case of irradiation in water, the seldom investigated effects of the immersion time, after irradiation with a fixed number of pulses, is analyzed, and an intriguing dependence of the color of the chromatic annuli on the immersion time is observed. This remarkable behavior is explained by proposing an interpretation scenario addressing the various processes involved in the process. Our experimental findings show that cuprous oxide nanoparticles (size of ~20 nm) and cuprous oxide nanocubes (nanocube edges of ~30, ~60 nm) with extremely fine sizes can be effectively generated by exploiting high repetition rate laser-assisted oxidation., Comment: 30 pages, 10 figures