Limits to compression with cascaded quadratic soliton compressors

We study cascaded quadratic soliton compressors and address the physical mechanisms that limit the compression. A nonlocal model is derived, and the nonlocal response is shown to have an additional oscillatory component in the nonstationary regime when the group-velocity mismatch (GVM) is strong. This inhibits efficient compression. Raman-like perturbations from the cascaded nonlinearity, competing cubic nonlinearities, higher-order dispersion, and soliton energy may also limit compression, and through realistic numerical simulations we point out when each factor becomes important. We find that it is theoretically possible to reach the single-cycle regime by compressing high-energy fs pulses for wavelengths $\lambda=1.0-1.3 \mu{\rm m}$ in a $\beta$-barium-borate crystal, and it requires that the system is in the stationary regime, where the phase mismatch is large enough to overcome the detrimental GVM effects. However, the simulations show that reaching single-cycle duration is ultimately inhibited by competing cubic nonlinearities as well as dispersive waves, that only show up when taking higher-order dispersion into account.Comment: 16 pages, 5 figures, submitted to Optics Expres

Measuring the mass of a sterile neutrino with a very short baseline reactor experiment

An analysis of the world's neutrino oscillation data, including sterile neutrinos, (M. Sorel, C. M. Conrad, and M. H. Shaevitz, Phys. Rev. D 70, 073004) found a peak in the allowed region at a mass-squared difference $\Delta m^2 \cong 0.9$ eV$^2$. We trace its origin to harmonic oscillations in the electron survival probability $P_{ee}$ as a function of L/E, the ratio of baseline to neutrino energy, as measured in the near detector of the Bugey experiment. We find a second occurrence for $\Delta m^2 \cong 1.9$ eV$^2$. We point out that the phenomenon of harmonic oscillations of $P_{ee}$ as a function of L/E, as seen in the Bugey experiment, can be used to measure the mass-squared difference associated with a sterile neutrino in the range from a fraction of an eV$^2$ to several eV$^2$ (compatible with that indicated by the LSND experiment), as well as measure the amount of electron-sterile neutrino mixing. We observe that the experiment is independent, to lowest order, of the size of the reactor and suggest the possibility of a small reactor with a detector sitting at a very short baseline.Comment: 4 pages, 2 figure

Optical vault: reconfigurable bottle beam by conically refracted light

We employ conical refraction of light in a biaxial crystal to create an optical bottle for trapping and manipulation of particles. We show that by just varying the polarization of the input light the bottle can be opened and closed at will. We experimentally demonstrate stable photophoretic trapping and controllable loading and unloading of light absorbing particles in the trap.Comment: 4 pages, 5 figure

Collapse in the nonlocal nonlinear Schr\"odinger equation

We discuss spatial dynamics and collapse scenarios of localized waves governed by the nonlinear Schr\"{o}dinger equation with nonlocal nonlinearity. Firstly, we prove that for arbitrary nonsingular attractive nonlocal nonlinear interaction in arbitrary dimension collapse does not occur. Then we study in detail the effect of singular nonlocal kernels in arbitrary dimension using both, Lyapunoff's method and virial identities. We find that for for a one-dimensional case, i.e. for $n=1$, collapse cannot happen for nonlocal nonlinearity. On the other hand, for spatial dimension $n\geq2$ and singular kernel $\sim 1/r^\alpha$, no collapse takes place if $\alpha<2$, whereas collapse is possible if $\alpha\ge2$. Self-similar solutions allow us to find an expression for the critical distance (or time) at which collapse should occur in the particular case of $\sim 1/r^2$ kernels. Moreover, different evolution scenarios for the three dimensional physically relevant case of Bose Einstein condensate are studied numerically for both, the ground state and a higher order toroidal state with and without an additional local repulsive nonlinear interaction. In particular, we show that presence of an additional local repulsive term can prevent collapse in those cases

Generation of the second-harmonic Bessel beams via nonlinear Bragg diffraction

We generate conical second-harmonic radiation by transverse excitation of a two-dimensional annular periodically-poled nonlinear photonic structure with a fundamental Gaussian beam. We show that these conical waves are the far-field images of the Bessel beams generated in a crystal by parametric frequency conversion assisted by nonlinear Bragg diffraction.Comment: 4 pages, 5 figures. submitte

Local demands on sterile neutrinos

In a model independent manner, we explore the local implications of a single neutrino oscillation measurement which cannot be reconciled within a three-neutrino theory. We examine this inconsistency for a single region of baseline to neutrino energy $L/E$. Assuming that sterile neutrinos account for the anomaly, we find that the {\it local} demands of this datum can require the addition to the theory of one to three sterile neutrinos. We examine the constraints which can be used to determine when more than one neutrino would be required. The results apply only to a given region of $L/E$. The question of the adequacy of the sterile neutrinos to satisfy a global analysis is not addressed here. Finally, using the results of a 3+2 analysis, we indicate values for unknown mixing matrix elements which would require two sterile neutrinos due to local demands only.Comment: 11 pages, 1 figure, discussion adde

Anisotropic charge displacement supporting isolated photorefractive optical needles

The strong asymmetry in charge distribution supporting a single non-interacting spatial needle soliton in a paraelectric photorefractive is directly observed by means of electroholographic readout. Whereas in trapping conditions a quasi-circular wave is supported, the underlying double-dipolar structure can be made to support two distinct propagation modes.Comment: 3 pages, 3 figure

Nonlinear Bloch-wave interaction and Bragg scattering in optically-induced lattices

We study, both theoretically and experimentally, the Bragg scattering of light in optically-induced photonic lattices and reveal the key physical mechanisms which govern nonlinear self-action of narrow beams under the combined effects of Bragg scattering and wave diffraction, allowing for selecting bands with different effective dispersion.Comment: 4 pages, 6 figure

Helmholtz bright and boundary solitons

We report, for the first time, exact analytical boundary solitons of a generalized cubic-quintic Non-Linear Helmholtz (NLH) equation. These solutions have a linked-plateau topology that is distinct from conventional dark soliton solutions; their amplitude and intensity distributions are spatially delocalized and connect regions of finite and zero wave-field disturbances (suggesting also the classification as 'edge solitons'). Extensive numerical simulations compare the stability properties of recently-reported Helmholtz bright solitons, for this type of polynomial non-linearity, to those of the new boundary solitons. The latter are found to possess a remarkable stability characteristic, exhibiting robustness against perturbations that would otherwise lead to the destabilizing of their bright-soliton counterpart

Reduced-symmetry two-dimensional solitons in photonic lattices

We demonstrate theoretically and experimentally a novel type of localized beams supported by the combined effects of total internal and Bragg reflection in nonlinear two-dimensional square periodic structures. Such localized states exhibit strong anisotropy in their mobility properties, being highly mobile in one direction and trapped in the other, making them promising candidates for optical routing in nonlinear lattices.Comment: 5 pages, 4 figure