Qian Kong

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.

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.

Theoretical investigations of nonlinear Raman–Nath diffraction in the frequency doubling process

We theoretically study the second-harmonic generation via nonlinear Raman–Nath diffraction in an optical medium with the spatial modulation of quadratic nonlinearity. We derive analytical equations that govern the emission properties of this nonlinear wave phenomenon. We also discuss how a substantial range of parameters such as the thickness of a nonlinear medium and the condition of a pump laser affect the strength of the emitted harmonic signals.

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.

Wavelength and position tuning of Čerenkov second-harmonic generation in optical superlattice

We study experimentally the Cerenkov second-harmonic generation in an optical superlattice formed in periodically poled lithium niobate crystal. We demonstrate strong sensitivity of the Cerenkov signal to the wavelength, diameter, and position of the incident fundamental beam. We model the observed behavior by using simple approach based on multiple interference of second harmonic signals emitted from the vicinity of the domain walls.

Suppression of collapse for two-dimensional Airy beam in nonlocal nonlinear media

Dynamics and collapse of two-dimensional Airy beams are investigated numerically in nonlocal nonlinear media with split step Fourier transform method. In particular, the stability and self-healing properties of the Airy beams depend crucially on the location and topological charge of the vortex when the beams carry angular momentum. The propagation of abruptly autofocusing Airy beams is also demonstrated in local and nonlocal media. In strongly self-focusing regime, with the help of nonlocality, stationary propagation of two-dimensional Airy beams can be obtained, which always collapse in local nonlinear media.

Dark solitons in nonlinear media with arbitrary degree of nonlocality

Spatial dark optical solitons are localized light intensity dips in the infinite constant background [1]. They exist as a result of a balance between diffraction and nonlinearity of the medium. In recent years there has been strong interest in the so-called nonlocal nonlinearities, in which the nonlinearity in a particular spatial location is determined by the light intensity in a certain neighborhood of this location.

Čerenkov second harmonic generation in nonlinear crystals

We investigate the role of the fundamental beam width on Cerenkov second harmonic generation in periodically poled crystal. We show that broader beam yields stronger signal and enhanced wavelength sensitivity of the emission process.