Nonlinear optical response and exciton dephasing in quantum dots

The full time-dependent four-wave mixing polarization in quantum dots is microscopically calculated, taking into account acoustic phonon-assisted transitions between different exciton states of the dot. It is shown that quite different dephasing times of higher exciton states in pancake anisotropic InGaAs quantum dots are responsible for the experimentally observed [1] double-exponential decay in the photon echo signal.Comment: NOEKS-8 contribution; 4 pages, 3 figure

Memory and correlation effects in the exciton-phonon kinetics

Memory and correlation effects in the interband absorption from quantum wells due to exciton-phonon dynamics are investigated. They are traced back to the frequency dependence and matrix character of the self energy arising in a 2nd Born theory. It is found that interpeak absorption increases with respect to the case in which this memory and correlation effects are neglected.Comment: NOEKS8 Proceeding

Disordered Eating Habits, Emotion Regulation, and Theory of Mind in Undergraduate Students

Theory of Mind (ToM), the ability to recognize and attribute mental states to oneself and others, has been found to be impaired in a number of different psychological disorders (Bora et al. 2009). Evaluating ToM in a population suffering from eating disorders, however, has proven less consistent; some Anorexia Nervosa patients show ToM deficits compared to healthy controls (Russell et al. 2009) and others perform similarly (Tchanturia et al. 2004). A common consensus not only seems to be lacking within the literature on ToM and Anorexia Nervosa, but within the broader family of eating disorders as well (e.g., Bulimia Nervosa; Medina-Pradas et al. 2012). Furthermore, due to a lack of research, it remains unclear how ToM relates to dysfunctional eating habits that don’t meet DSM-5 criteria for an eating disorder. The role of emotion regulation (ER) appears promising in accounting for some of these discrepancies. The current thesis hypothesized first that ToM would be correlated with higher eating disorder symptomology and second that ER would mediate the relationship between ToM abilities and eating disorder symptomology. Neither of the current hypotheses were supported. However, an exploratory analysis revealed significant relationships between the eating disorder measures used and specific subscales of the DERS (between the RS and the lack of emotional awareness/limited access to strategies subscales and between the EA and nonacceptance of emotions subscale). Implications for future research and application to treatment are discussed

Topological characterization of antireflective and hydrophobic rough surfaces: are random process theory and fractal modeling applicable?

The random process theory (RPT) has been widely applied to predict the joint probability distribution functions (PDFs) of asperity heights and curvatures of rough surfaces. A check of the predictions of RPT against the actual statistics of numerically generated random fractal surfaces and of real rough surfaces has been only partially undertaken. The present experimental and numerical study provides a deep critical comparison on this matter, providing some insight into the capabilities and limitations in applying RPT and fractal modeling to antireflective and hydrophobic rough surfaces, two important types of textured surfaces. A multi-resolution experimental campaign by using a confocal profilometer with different lenses is carried out and a comprehensive software for the statistical description of rough surfaces is developed. It is found that the topology of the analyzed textured surfaces cannot be fully described according to RPT and fractal modeling. The following complexities emerge: (i) the presence of cut-offs or bi-fractality in the power-law power-spectral density (PSD) functions; (ii) a more pronounced shift of the PSD by changing resolution as compared to what expected from fractal modeling; (iii) inaccuracy of the RPT in describing the joint PDFs of asperity heights and curvatures of textured surfaces; (iv) lack of resolution-invariance of joint PDFs of textured surfaces in case of special surface treatments, not accounted by fractal modeling.Comment: 21 pages, 13 figure

Reinforcement of wood with natural fibers

This paper describes an experimental programme which examines the reinforcement in flexure of timber beams with composite materials based on natural fibers in the form of fabrics made from hemp, flax, basalt and bamboo fibers. The industrial use of natural fibers has been continuously increasing since 1990s due to their advantages in terms of production costs, pollution emissions and energy consumption for production and disposal. The technique allows the reinforcement of the intrados of beams, avoiding the dismantling of the overlying part of the structure with significant savings in terms of costs and work time. The test program consists of three phases incorporating 45 beams. The bending tests on the wooden elements made it possible to measure the increase in capacity and stiffness resulting from the composite reinforcement. This was applied to beams, creating different arrangements and using different quantities (number of layers). Despite the diversity of the various tests carried out, the results obtained in some cases showed significant increases in terms of load-carrying capacity and in deflection ductility

Femtosecond phase-resolved microscopy of plasmon dynamics in individual gold nanospheres

The selective optical detection of individual metallic nanoparticles (NPs) with high spatial and temporal resolution is a challenging endeavour, yet is key to the understanding of their optical response and their exploitation in applications from miniaturised optoelectronics and sensors to medical diagnostics and therapeutics. However, only few reports on ultrafast pump-probe spectroscopy on single small metallic NPs are available to date. Here, we demonstrate a novel phase-sensitive four-wave mixing (FWM) microscopy in heterodyne detection to resolve for the first time the ultrafast changes of real and imaginary part of the dielectric function of single small (<40nm) spherical gold NPs. The results are quantitatively described via the transient electron temperature and density in gold considering both intraband and interband transitions at the surface plasmon resonance. This novel microscopy technique enables background-free detection of the complex susceptibility change even in highly scattering environments and can be readily applied to any metal nanostructure

Polarization-resolved extinction and scattering cross-section of individual gold nanoparticles measured by wide-field microscopy on a large ensemble

We report a simple, rapid, and quantitative wide-field technique to measure the optical extinction $\sigma_{\rm ext}$ and scattering $\sigma_{\rm sca}$ cross-section of single nanoparticles using wide-field microscopy enabling simultaneous acquisition of hundreds of nanoparticles for statistical analysis. As a proof of principle, we measured nominally spherical gold nanoparticles of 40\,nm and 100\,nm diameter and found mean values and standard deviations of $\sigma_{\rm ext}$ and $\sigma_{\rm sca}$ consistent with previous literature. Switching from unpolarized to linearly polarized excitation, we measured $\sigma_{\rm ext}$ as a function of the polarization direction, and used it to characterize the asphericity of the nanoparticles. The method can be implemented cost-effectively on any conventional wide-field microscope and is applicable to any nanoparticles

On the interpretation of wave function overlaps in quantum dots

The spontaneous emission rate of excitons strongly confined in quantum dots is proportional to the overlap integral of electron and hole envelope wave functions. A common and intuitive interpretation of this result is that the spontaneous emission rate is proportional to the probability that the electron and the hole are located at the same point or region in space, i.e. they must coincide spatially to recombine. Here we show that this interpretation is not correct even loosely speaking. By general mathematical considerations we compare the envelope wave function overlap, the exchange overlap integral, and the probability of electrons and holes coinciding and find that the frequency dependence of the envelope wave function overlap integral is very different from that expected from the common interpretation. We show that these theoretical considerations lead to predictions for measurements. We compare our qualitative predictions with recent measurements of the wave function overlap and find good agreement.Comment: 4 pages, 3 figure