Effects of disorder on propagation losses and cavity Q-factors in photonic crystal slabs

A theoretical model of disorder for the etched holes or pillars in a generic two-dimensional photonic crystal slab is presented. This model is employed to calculate the effects of size disorder on propagation losses in linear photonic crystal waveguides as well as on quality (Q)-factors in photonic crystal nano-cavities. The main results obtained by the present theory and shown in this work are: (a) large single-mode bandwidth and low-loss (<0.1 dB/mm) propagation of light is predicted for increased-width membrane-type photonic crystal waveguides, (b) pillar-based lattices show reduced sensitivity to size fluctuations than hole-based ones, (c) the effects of disorder on cavity Q-factors are quantitatively evaluated. An extension of the model is also introduced in order to take into account the side-wall micro-roughness of the perfectly vertical holes, and preliminary results of this more general approach are discussed.     

A goldstone mode in the Kawasaki-Ising model

The hydrodynamic regime of superfluids is dominated by a Goldstone mode corresponding to a spontaneously brokenU(1) symmetry. In this article we map the Kawasaki-Ising model for a classical lattice gas into a quantum model for a superfluid and establish a connection between the normal density fluctuations of the first and the Goldstone mode of the second. The fact that the quantum model we obtain describes a superfluid derives from an inequality by Penrose and Onsager which gives a lower bound to the Bose-Einstein condensate density. Mathematically, the Goldstone mode can be described by means of a quantum extension of the local algebra of the Ising model. The classification of its irreducible representations requires an additionalU(1) phase factor and the correspondingU(1) gauge symmetry is spontaneously broken for all finite values of the temperature and of the density.     

Programming scale-free optics in disordered ferroelectrics

Using the history dependence of a dipolar glass hosted in a compositionally disordered lithium-enriched potassium tantalate niobate (KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable temperatures. The operating equilibration temperature is determined by previous crystal spiralling in the temperature/cooling-rate phase space.     

Interface Energy in the Edwards-Anderson Model

We numerically investigate the spin glass energy interface problem in three dimensions. We analyze the energy cost of changing the overlap from −1 to +1 at one boundary of two coupled systems (in the other boundary the overlap is kept fixed to +1). We implement a parallel tempering algorithm that simulates finite temperature systems and works with both cubic lattices and parallelepiped with fixed aspect ratio. We find results consistent with a lower critical dimension D _c =2.5. The results show a good agreement with the mean field theory predictions.     

Use of apodization in quantitative spectroscopy

Apodization, which is a tool frequently used for cosmetic representation and efficient modeling of a spectrum, is now also adopted in techniques for the quantitative retrieval of parameters from observed spectra. Whether apodization can help in quantitative spectroscopy is the subject of debate in the literature. We find that, when the considered spectral range is wide enough to accurately model the instrument line shape, the same results can be obtained with and without apodization of the spectrum. However, when a truncation error is introduced by the limited extension of the modeled spectral interval, apodization can efficiently reduce this error. Therefore it is possible to save computing time by using apodization.     

Ultrasound promoted synthesis of thioesters from 2-mercaptobenzoxa(thia)zoles

An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields.     

Complex dynamics and configurational entropy of spatial optical solitons in nonlocal media

Intense light propagating in a nonlinear medium can generate an ensemble of interacting filaments of light, or spatial solitons. Using nematic liquid crystals, we demonstrate that the filaments exhibit collective behavior typical of complex systems, including the formation of clusters and soundlike vibrations, as well as the reduction of the configurational entropy, controlled by the degree of nonlocality of the medium.     

High-spectral-resolution coherent anti-Stokes Raman scattering with interferometrically detected broadband chirped pulses

To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering.