Optical pattern formation with a 2-level nonlinearity

We present an experimental and theoretical investigation of spontaneous pattern formation in the transverse section of a single retro-reflected laser beam passing through a cloud of cold Rubidium atoms. In contrast to previously investigated systems, the nonlinearity at work here is that of a 2-level atom, which realizes the paradigmatic situation considered in many theoretical studies of optical pattern formation. In particular, we are able to observe the disappearance of the patterns at high intensity due to the intrinsic saturable character of 2-level atomic transitions.Comment: 5 pages, 4 figure

Realization of a semiconductor-based cavity soliton laser

The realization of a cavity soliton laser using a vertical-cavity surface-emitting semiconductor gain structure coupled to an external cavity with a frequency-selective element is reported. All-optical control of bistable solitonic emission states representing small microlasers is demonstrated by injection of an external beam. The control scheme is phase-insensitive and hence expected to be robust for all-optical processing applications. The motility of these structures is also demonstrated

Spatial correlations in hexagons generated via a Kerr nonlinearity

We consider the hexagonal pattern forming in the cross-section of an optical beam produced by a Kerr cavity, and we study the quantum correlations characterizing this structure. By using arguments related to the symmetry broken by the pattern formation, we identify a complete scenario of six-mode entanglement. Five independent phase quadratures combinations, connecting the hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of a non-linear quantum calculation technique, quantum correlations among the mode photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure

Large optical gain from four-wave mixing instabilities in semiconductor quantum wells

Based on a microscopic many-particle theory, we predict large optical gain in the probe and background-free four-wave mixing directions caused by excitonic instabilities in semiconductor quantum wells. For a single quantum well with radiative-decay limited dephasing in a typical pump-probe setup we discuss the microscopic driving mechanisms and polarization and frequency dependence of these instabilities

All-optical delay line using semiconductor cavity solitons (vol 92, 011101, 2008)

Correction of Pedaci, F. and Barland, S. and Caboche, E. and Firth, W.J. and Oppo, G.L. and Tredicce, J.R. and Ackemann, T. and Scroggie, A.J. (2008) All-optical delay line using semiconductor cavity solitons. Applied Physics Letters, 92 (1). ISSN 0003-695

Frequency selection by soliton excitation in nondegenerate intracavity downconversion

We show that soliton excitation in intracavity downconversion naturally selects a strictly defined frequency difference between the signal and idler fields. In particular, this phenomenon implies that if the signal has smaller losses than the idler then its frequency is pulled away from the cavity resonance and the idler frequency is pulled towards the resonance and {\em vice versa}. The frequency selection is shown to be closely linked with the relative energy balance between the idler and signal fields.Comment: 5 pages, 3 figures. To appear in Phys Rev Let

Quantum threshold for optomechanical self-structuring in a Bose-Einstein condensate

Theoretical analysis of the optomechanics of degenerate bosonic atoms with a single feedback mirror shows that self-structuring occurs only above an input threshold that is quantum mechanical in origin. This threshold also implies a lower limit to the size (period) of patterns that can be produced in a condensate for a given pump intensity. These thresholds are interpreted as due to the quantum rigidity of Bose-Einstein condensates, which has no classical counterpart. Above the threshold, the condensate self-organizes into an ordered supersolid state with a spatial period self-selected by optical diffraction

Stability of vortex solitons in a photorefractive optical lattice

Stability of off-site vortex solitons in a photorefractive optical lattice is analyzed. It is shown that such solitons are linearly unstable in both the high and low intensity limits. In the high-intensity limit, the vortex looks like a familiar ring vortex, and it suffers oscillatory instabilities. In the low-intensity limit, the vortex suffers both oscillatory and Vakhitov-Kolokolov instabilities. However, in the moderate-intensity regime, the vortex becomes stable if the lattice intensity or the applied voltage is above a certain threshold value. Stability regions of vortices are also determined at typical experimental parameters.Comment: 3 pages, 5 figure

Evidence for a novel coding sequence overlapping the 5'-terminal ~90 codons of the Gill-associated and Yellow head okavirus envelope glycoprotein gene

The genus Okavirus (order Nidovirales) includes a number of viruses that infect crustaceans, causing major losses in the shrimp industry. These viruses have a linear positive-sense ssRNA genome of ~26-27 kb, encoding a large replicase polyprotein that is expressed from the genomic RNA, and several additional proteins that are expressed from a nested set of 3'-coterminal subgenomic RNAs. In this brief report, we describe the bioinformatic discovery of a new, apparently coding, ORF that overlaps the 5' end of the envelope glycoprotein encoding sequence, ORF3, in the +2 reading frame. The new ORF has a strong coding signature and, in fact, is more conserved at the amino acid level than the overlapping region of ORF3. We propose that translation of the new ORF initiates at a conserved AUG codon separated by just 2 nt from the ORF3 AUG initiation codon, resulting in a novel 86 amino acid protein