Qi Wang

Analytical theory for the dark-soliton interaction in nonlocal nonlinear materials with an arbitrary degree of nonlocality

We investigate theoretically the interaction of dark solitons in materials with a spatially nonlocal nonlinearity. In particular we do this analytically and for arbitrary degree of nonlocality. We employ the variational technique to show that nonlocality induces an attractive force in the otherwise repulsive soliton interaction.

Analytical theory of dark nonlocal solitons.

We investigate properties of dark solitons in nonlocal materials with an arbitrary degree of nonlocality. We employ the variational technique and describe dark solitons, for the first time to our knowledge, in the whole range of degree of nonlocality.

Nonlocal dark solitons under competing cubic–quintic nonlinearities

We investigate properties of dark solitons under competing nonlocal cubic-local quintic nonlinearities. Analytical results, based on a variational approach and confirmed by direct numerical simulations, reveal the existence of a unique dark soliton solutions with their width being independent of the degree of nonlocality, due to the competing cubic-quintic nonlinearities.

Theoretical study of Čerenkov-type second-harmonic generation in periodically poled ferroelectric crystals

We study theoretically the Cerenkov-type second-harmonic generation by a Gaussian beam in quadratic nonlinear media with periodically reverted ferroelectric domains. In particular, we consider the role of fundamental beam width on the harmonic emission process. We show that varying the beam width of the fundamental wave not only affects the strength of the emitted Cerenkov harmonic signal but also changes the sensitivity of the emission process to wavelength tuning.

Interactions of nonlocal dark solitons under competing cubic–quintic nonlinearities

We investigate analytically and numerically the interactions of dark solitons under competing nonlocal cubic and local quintic nonlinearities. It is shown that the self-defocusing quintic nonlinearity will strengthen the attractive interaction and decrease the relative distance between solitons, whereas the self-focusing quintic nonlinearity will enhance the repulsive interaction and increase soliton separation. We demonstrate these results by approximate variational approach and direct numerical simulation.

Negative phase time for particles passing through a potential well

Abstract It is reported that the phase time of particles passing through a potential well is negative when the energy of incident particles and the thickness of potential well satisfy certain conditions. Similar results are also found in a fully-relativistic optical analog. The 2-dimensional optical case gives rise to a lateral shift of the wave packet. It is shown that the phase-time associated lateral shift can also be negative.

Tailoring Čerenkov second-harmonic generation in bulk nonlinear photonic crystal.

We investigate theoretically the Čerenkov-type second-harmonic generation in two-dimensional bulk nonlinear photonic crystal with longitudinal modulation of the χ((2)) nonlinearity. We show that in this scheme the Čerenkov radiation can be achieved simultaneously at multiple directions with comparable intensities. The angles of emission are controllable by the spatial modulation of the nonlinearity. We propose a design of the periodically poled domain pattern, which maximizes the efficiency of the second-harmonic emission.

Amorphous physics and materials: Secondary relaxation and dynamic heterogeneity in metallic glasses: A brief review*

Understanding mechanical relaxation, such as primary (a) and secondary (s) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, s relaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of s relaxation. In particular, we will discuss the correlation among s relaxation, structural heterogeneity, and mechanical properties of metallic glasses.

Dark solitons in nonlocal media: variational analysis

The propagation of dark solitons is systematically investigated in a weakly nonlocal self-defocusing Kerr-type nonlinear medium. Based on the variational principle, we get an analytical solution of such nonlocal dark solitons. We also clearly give the expression describing the transverse velocity of the dark solitons. We find that the width of the dark solitons is related to the degree of nonlocality and the grayness of the solitons, that there exists a threshold of the degree of nonlocality for such nonlocal dark solitons, and that, as the degree of nonlocality increases, the solitons velocity will decrease. We also demonstrate the stability of the nonlocal dark solitons.

Photon tunnelling in one-dimensional metamaterial photonic crystals

Photon tunnelling in a metamaterial photonic crystal composed by positive index material (PIM) and negative index material (NIM) layers is discussed. First, a single period of this photonic crystal is considered as the barrier in a frustrated total internal reflection (FTIR) structure, and the transmittance, the post-tunnelling position shift and the group delay time of different frequency incident waves through the barrier are calculated. In the case of a barrier of more periods of photonic crystal, the transmittance and the group delay time also vary with layer number, which are analysed in detail.