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

We performed quasiresonant laser excitation of lithium vapor and lithium-zinc (cadmium) vapor mixture at 460.3 nm and 497.2 nm. Different processes producing initial Li(2p) level population are identified and discussed. In lithium-zinc (cadmium) vapor mixture three-body reactive collision of excited atoms is found responsible for formation of the excited LiZn or LiCd dimers.

Quasiresonant excitation of lithium vapor

A mode-locked fs laser is used to map the laser frequency comb into the velocity comb of the Rb atoms at room temperature. Modified DFCS is developed and density matrix treatment is used.

Mapping of the Optical Frequency Comb to the Atom Velocity Comb

Objective: The purpose of this article was to investigate a new setup for tooth bleaching and monitoring of the same process in real time, so to prevent overbleaching and related sideeffects of the bleaching procedure. Background data: So far, known bleaching procedures cannot simultaneously monitor and perform the bleaching process or provide any local control over bleaching. Materials and methods: The experimental setup was developed at the Institute of Physics, Zagreb. The setup consists of a camera, a controller, and optical fibers. The bleaching was performed with 25% hydrogen peroxide activated by ultraviolet light diodes, and the light for monitoring was emitted by white light diodes. The collected light was analyzed using a red-green-blue (RGB) index. A K-type thermocouple was used for temperature measurements. Pastilles made from hydroxylapatite powder as well as human teeth served as experimental objects. Results: Optimal bleaching time substantially varied among differently stained spe...

Real-time local experimental monitoring of the bleaching process.

Our most recent absorption and emission experiments with heavy alkali vapor using super bright light-emitting diodes from NICHIA, LUMILED and OSRAM will be presented. UV LEDs together with LEDs in the visible spectral region present invaluable narrow-band continuum light source for very precise absorption measurements. We used all-sapphire cells and heat-pipe oven cells in usual absorption arrangement with high resolution scanning monochromators. Beside self-broadened alkali resonance lines, we investigated molecular bands and diffuse bands of alkali dimers. A number of applications, especially in dentistry will be also presented.

Atomic and Molecular Spectroscopy with UV and Visible Superbright LEDs

We performed quasiresonant laser excitation of lithium vapor and lithium-zinc (cadmium) vapor mixture at 4603 nm and 4972 nm Different processes producing initial Li(2p) level population are identified and discussed In lithium-zinc (cadmium) vapor mixture three-body reactive collision of excited atoms is found responsible for formation of the excited LiZn or LiCd dimers Quasiresonant laser excitation offers an interesting way to produce highly excited atoms in a vapor mixture It is generally a process in which laser photon absorption starts from an excited atomic level The initial excited atomic level population is obtained through the accidental resonance with molecular transitions followed by various processes such as collisionally or radiatively induced dissociation or energy transfer In the Li+Li2 system, the quasiresonant excitation has not been studied in details, but was used in laser-induced plasma experiments [1,2], and laser ignition of the glow discharge [3] In this work we performed quasiresonant laser excitation of pure lithium vapor and Li-Zn or Li-Cd vapor mixtures at 4603 nm (2p-4d) and 4972 nm (2p-4s) The initial population of Li(2p) level is caused by three processes: collisional dissociation or photodissociation of the Lia B! molecules or energy transfer in Li2 (B!^) and Li(2s) collisions Relevant processes are illustrated in Fig 1 for the case of 4603 nm laser excitation A pulsed dye laser working with Coumarin 102 dye (range 460-510 nm) pumped by a XeCl excimer laser was used for the excitation The laser bandwith was about 6 GHz The laser induced fluorescence was dispersed by a 06 m scanning monochromator, and the signal from a photomultiplier was averaged by a boxcar averager, converted to a digital signal through an A/D converter and fed to a PC computer We have used absorption spectroscopy and selective wavelength excitation spectroscopy to study line shapes of the relevant resonances and obtain details of the excitation processes Experimental results are supported with detailed spectral simulations using most recent potential energy curves [4] We have identifed several molecular transitions to be resonant with 2p-4d or 2p-4s atomic transitions The Li(4d,4s) atoms radiatively decay towards Li(3p) In intermetallic mixtures, either Li(4d) and Li(4s) or Li(3p) and Li(3d) are involved in collisional population transfer to Zn(4Pj) and Cd(5Pj), respectively Population of these metastable levels is CP559, Spectral Line Shapes: Volume 11, 15 ICSLS, edited by J Seidel © 2001 American Institute of Physics 1-56396-991-2/017$ 1800 431 followed by three-body reactive collisions, which produce the LiZn or LiCd 2 IT excimer states [4] To observe these excimer emissions we have found that temporally resolved fluorescence observation is important, because of the spectral overlap with lithium dimer molecular emission

Goran Pichler

Papers

Quasiresonant excitation of lithium vapor

Mapping of the Optical Frequency Comb to the Atom Velocity Comb

Real-time local experimental monitoring of the bleaching process.

Atomic and Molecular Spectroscopy with UV and Visible Superbright LEDs

Quasiresonant excitation of lithium vapor