Femtosecond filamentation in transparent media

There is growing interest in states of matter with topological order. These are characterized by highly stable ground states robust to perturbations that preserve the topology, and which support excitations with so-called anyonic statistics. Topologically ordered states can arise in two-dimensional lattice-spin models, which were proposed as the basis for a new class of quantum computation. Here, we show that the relevant hamiltonians for such spin lattice models can be systematically engineered with polar molecules stored in optical lattices, where the spin is represented by a single-valence electron of a heteronuclear molecule. The combination of microwave excitation with dipole–dipole interactions and spin–rotation couplings enables building a complete toolbox for effective two-spin interactions with designable range, spatial anisotropy and coupling strengths significantly larger than relevant decoherence rates. Finally, we illustrate two models: one with an energy gap providing for error-resilient qubit encoding, and another leading to topologically protected quantum memory.

https://arxiv.org/pdf/quant-ph/0512222.pdf

A toolbox for lattice-spin models with polar molecules

The authors review progress in understanding the nature of atomic collisions occurring at temperatures ranging from the millidegrees Kelvin to the nanodegrees Kelvin regime. The review includes advances in experiments with atom beams, light traps, and purely magnetic traps. Semiclassical and fully quantal theories are described and their appropriate applicability assessed. The review divides the subject into two principal categories: collisions in the presence of one or more light fields and ground-state collisions in the dark.

Experiments and theory in cold and ultracold collisions

Photoassociation is the process in which two colliding atoms absorb a photon to form an excited molecule. The development of laser-cooling techniques for producing gases at ultracold !!1 mK" temperatures allows photoassociation spectroscopy to be performed with very high spectral resolution. Of particular interest is the investigation of molecular states whose properties can be related, with high precision, to the properties of their constituent atoms with the “complications” of chemical binding accounted for by a few parameters. These include bound long-range or purely long-range vibrational states in which two atoms spend most or all of their time at large internuclear separations. Low-energy atomic scattering states also share this characteristic. Photoassociation techniques have made important contributions to the study of all of these. This review describes what is special about photoassociation spectroscopy at ultracold temperatures, how it is performed, and a sampling of results including the determination of scattering lengths, their control via optical Feshbach resonances, precision determinations of atomic lifetimes from molecular spectra, limits on photoassociation rates in a Bose-Einstein condensate, and briefly, production of cold molecules. Discussions are illustrated with examples on alkali-metal atoms as well as other species. Progress in the field is already past the point where this review can be exhaustive, but an introduction is provided on the capabilities of photoassociation spectroscopy and the techniques presently in use.

/pdf/ultracold-photoassociation-spectroscopy-long-range-molecules-31d6x6vqxx.pdf

Ultracold photoassociation spectroscopy: Long-range molecules and atomic scattering

Summary: Carbazole-based oligomeric and polymeric materials have been studied for almost 25 years for their unique electrical, electrochemical and optical properties. Interestingly, carbazole units can be linked in two different ways leading to either poly(3,6-carbazole) or poly(2,7-carbazole) derivatives. While the former class seems to be very interesting for electrochemical and phosphorescence applications, the latter shows very promising optical properties in the visible range for light emitting diodes (LED). The major intrinsic difference between these two classes is the effective conjugation length: poly(2,7-carbazole) materials having the longer one, due to their poly(p-phenylene)-like structure. Using different synthetic strategies and substitution patterns, the physico-chemical properties of both classes can be fine-tuned, leading to high performance materials for a large number electronic applications.

Chemical structures for poly(3,6-carbazole) and poly(2,7-carbazole) and the materials used as the starting points for their respective syntheses.

Polycarbazoles: 25 Years of Progress

To ensure an adequate clinical composite filling light source for photopolymerization is of great importance. In everyday clinical conditions commonly used unit for polymerization of composite material is halogen curing unit. The development of new blue superbright light emitting diodes (LED) of 470 nm wavelengths comes as an alternative to standard halogen curing unit of 450-470 nm wavelengths. The purpose of this study was to compare the degree of conversion (DC) and temperature rise of four hybrid composite materials: Tetric Ceram, Pertac II, Valux Plus and Degufill Mineral during 40 s illumination with standard halogen curing unit Heliolux GTE of 600 mW cm(-2) intensity, Elipar Highlight soft-start curing unit of 100 mW cm(-2) (10 s) and 700 mW cm(-2) (30 s) intensity and 16 blue superbright LED of minimal intensity of 12 mW cm(-2) on the surface and 1 mm depth. The results revealed only a little bit higher DC values in case of polymerization with even 66 times stronger halogen curing units which showed twice higher temperature than blue diodes. Temperature and DC obtained are higher on the surface than on 1 mm depth regardless on the light source used.

Degree of conversion and temperature rise during polymerization of composite resin samples with blue diodes.

Clinical Relevance The use of a low intensity light source for photopolymerization based on LED technology provides equivalent final degree conversion with possible flow of the resin composite, similar to when QTH technology is used. At the same time, the lower temperature rise in the sample and the more favorable development of shrinkage kinetics compared to the higher intensities of halogen light may aid in maintaining marginal adaptation while avoiding possible thermal injury.

/pdf/comparison-of-composite-curing-parameters-effects-of-light-563do9tzl4.pdf

Comparison of Composite Curing Parameters: Effects of Light Source and Curing Mode on Conversion, Temperature Rise and Polymerization Shrinkage

The unavoidable consequence of composite resin photopolymerization is temperature rise in tooth tissue. The temperature rise depends not only on the illumination time, but also on light intensity, distance of light guide tip from composite resin surface, composition and shade of composite resin and composite thickness. The most commonly used units for polymerization today are halogen curing units, which emit a large spectrum of wavelengths. A proportion of the spectrum has no influence on degree of conversion and therefore causes unnecessary temperature rise. Units based on light source - blue light emitting diodes (LED), as an alternative for halogen curing units, have been introduced in clinical practice. The aim of this study was to show the influence of the light intensity of curing units Elipar Trilight, Astralis 7 and Lux-o-Max unit on temperature rise in composite resin sample of Tetric Ceram. The temperature was measurement with Metex M-3850 D multimeter with the tip of temperature probe put into unpolymerized composite resin sample 1 mm depth. The highest temperature rise was recorded with standard curing mode for Elipar Trilight halogen curing unit (13.3 +/- 1.21 degrees C after 40 s illumination), while the lowest temperature rise was recorded for the Lux-o-Max unit based on LED technology (5.2 +/- 1.92 degrees C after 40 s illumination).

http://members.ziggo.nl/willyonclin/Artikelen/2005.pdf

Influence of light intensity from different curing units upon composite temperature rise

The objective of this study was to evaluate the degree of conversion and temperature rise in three different composite materials when illuminated by an experimental light source [blue superbright light emitting diodes (LEDs)] and compared with plasma light and traditional photopolymerization unit. The degree of conversion and temperature rise were measured using Fourier transform infrared (FTIR) spectroscopy and digital multimeter, respectively. The results revealed significantly higher degree of conversion values in case of conventional curing than with other two light sources whereas temperature rise was significantly lower when blue LEDs and plasma light were used. There were great differences in light intensities between blue LEDs of only 9 mW cm-2 compared with plasma light of 1370 mW cm-2 and Elipar II of 560 mW cm-2. Better match of LED spectral distribution peak to camphorquinone absorption distribution peak probably explains much lower intensities used for similar photopolymerization effect like in the case of rapid plasma lamp curing.

Composite conversion and temperature rise using a conventional, plasma arc, and an experimental blue LED curing unit

Adiabatic potential curves were calculated using perturbation theory for the long-range electrostatic interaction between two alkali atoms of the same species, one being in the ground state, the other in the resonance-excited state. Comparison with recent experiments showed that the observed satellites and asymmetries in the self-broadened quasi-state wings of the alkali resonance lines are the consequence of extrema in certain potential curves between the fine-structure levels.

https://iopscience.iop.org/article/10.1088/0022-3700/10/13/016/pdf

Goran Pichler

Papers

Degree of conversion and temperature rise during polymerization of composite resin samples with blue diodes.

Comparison of Composite Curing Parameters: Effects of Light Source and Curing Mode on Conversion, Temperature Rise and Polymerization Shrinkage

Influence of light intensity from different curing units upon composite temperature rise

Composite conversion and temperature rise using a conventional, plasma arc, and an experimental blue LED curing unit

Resonance interaction and self-broadening of alkali resonance lines. I. Adiabatic potential curves