Fan Dianyuan

Controllable Raman soliton self-frequency shift in nonlinear metamaterials

Controllable and dispersive magnetic permeability in the metamaterials (MMs) provides us more freedom to harness the propagation of ultrashort electromagnetic pulses at will. Here we discuss the controllability of the Raman soliton self-frequency shift (SSFS) in the MMs with a nonlinear electric polarization. First, we derive a generalized nonlinear Schroedinger equation suitable for few-cycle pulse propagation in the MMs with delayed Raman response, and demonstrate the Raman effect, high-order Raman-related nonlinearity, and high-order nonlinear dispersion terms occurring in this equation. Second, we present a theoretical investigation on the controllability of the Raman SSFS in the MMs. In particular, we identify the combined effects of the anomalous self-steepening (SS), third-order dispersion (TOD), and Raman effect on SSFS. It is shown that the positive SS effect suppresses SSFS; however, the negative SS effect enhances SSFS, and the positive TOD leads to the deceleration of SSFS. Finally, the effects of SS on the SSFS of the second-order soliton are also discussed.

Effects of different ligands on luminescence properties of LaF3: Nd nanoparticles

A series of neodymium-doped lanthanum fluoride nanoparticles (NPs) were synthesized with hydrothermal method, and the effects of several ligands on the luminescence properties of the NPs were investigated. The X-ray diffraction (XRD) results indicated that the crystal phases of the modified NPs coincided with the standard spectrum. The transmission electron microscopy (TEM) showed that the samples were of similar size, shape and dispersibility. The infrared spectra suggested that the content of OH groups as quenchers on the NPs surfaces decreased after modification. Compared with NPs modified by branched paraffin ligands, NPs conjugating ring-contained modifiers had less quenching effect and possessed stronger fluorescence intensity and longer fluorescence lifetime.

Design and analysis of a kind of large flattened mode optical fibre

In this paper, a refractive index profile design enabling us to obtain a flat modal field around the fibre centre is investigated. The theoretical approach for designing such multilayer large flattened mode (LFM) optical fibres is presented. A comparison is made between the properties of a three-layer LFM structure and a standard step-index profile with the same core size. The obtained results indicate that the effective area of the LFM fibre is about twice as large as that of the standard step-index fibre, but the LFM fibre has less effective ability to filter out the higher order modes than the standard step-index fibre with the same bending radius.

Spatiotemporal Instability of Ultrashort Pulses in Dispersive Self-Focusing Media

Spatiotemporal instability in dispersive self-focusing media is investigated on the basis of a modified nonlinear Schrodinger equation (NLSE) beyond the slowly varying envelope approximation. It is found that, for both normal and anomalous dispersions, space-time focusing may lead to the appearance of new temporal instability regions for some range of spatial frequencies. The physical origin of the new instability regions lies in the part of space-time coupling related to the fourth-order dispersion. Furthermore, space-time focusing shrinks the instability regions and slightly reduces the maximum growth rates of the original spatiotemporal instability gain spectra obtained from the standard NLSE.

Filamentation instability of laser beams in nonlocal nonlinear media

The filamentation instability of laser beams propagating in nonlocal nonlinear media is investigated. It is shown that the filamentation instability can occur in weakly nonlocal self-focusing media for any degree of nonlocality and in defocusing media for the input light intensity exceeding a threshold related to the degree of nonlocality. A linear stability analysis is used to predict the initial growth rate of the instability. It is found that the nonlocality tends to suppress filamentation instability in self-focusing media and to stimulate filamentation instability in self-defocusing media. Numerical simulations confirm the results of the linear stability analysis and disclose a recurrence phenomenon in nonlocal self-focusing media analogous to the Fermi-Pasta-Ulam problem.

Small-Scale Self-Focusing of Intense Laser Beams In the Presence of Vector Effect

We extend Bespalov-Talanov (B-T) theory on small-scale self-focusing (SSSF) to include vector effect of a very narrow intense laser beam with application of the vector self-focusing model. The gain spectrum for perturbations is obtained by using the standard linear instability analysis. It is shown that the influence on SSSF of vector effect is closely related to the beam width. For a very narrow beam, the role played by vector effect becomes significant, it reduces the fastest growing frequency and the maximum growth rate, and shortens the frequency range for perturbation growing, and thus deviates the gain spectrum from that of B-T theory.

GENERALIZED FRESNEL DIFFRACTION INTEGRAL AND ITS APPLICATIONS

Within the generalized definition of ABCDGH matrices, the conventional ABCDGH diffraction integral is extended for a misaligned complex paraxial system with a curved optical axis. On this basis the transformation law for Gaussian-Schell model beams through an ABCDGH systems is derived, the propagation behavior of the mutual coherence function through ABCDGH systems in the presence of random media is investigated as well.

General design basis for a final optics assembly to decrease filamentary damage

The high-power laser beam in the final optics assembly of high-power laser facilities is often modulated by contamination particles, which may cause local high light intensity, thereby increasing the filamentary damage probability for optical components. To study the general design basis for a final optics assembly to decrease the risk of filamentary damage, different-sized contamination particles deposited on a component surface are simulated to modulate a 351-nm laser beam based on the optical transmission theory, and the corresponding simulation results are analyzed statistically in terms of the propagation characteristic and the light field intensity distribution of the modulated laser beam. The statistical results show that component thickness and distance between components can to some extent be optimized to reduce the appearance of local high light intensity, and the general design basis of component thickness and arrangement are given for different control levels of particle sizes. Moreover, the statistical results can also predict the laser beam quality approximately under the existing optics design and environmental cleanliness. The optimized design for final optics assembly based on environmental cleanliness level is useful to prolong the lifetime of optics and enhance the output power of high-power laser facilities.

Evaluate the Dispersion Parameters for Ultrashort Pulses Propagating in Photonic Crystals

Using the least-squares spline approximation to analyze the photonic band structure,the dispersion parameters of a two-dimensional photonic crystal are quantitatively calculated.Considering the large bandwidth of an ultrashort pulse,average group velocity and average group velocity dispersion are achieved by introducing a weighting factor,which reveals the share of different frequency components.So the pulse evolution can be predicted theoretically.Propagation of ultrashort pulses through the photonic crystals is simulated by using the finite-difference time-domain method.The results of numerical simulations are well consistent with the theoretical predictions.This process for achieving dispersion parameters is valuable for designing photonic-crystal dispersion devices such as dispersion compensator,pulse compressor and pulse stretcher.

Core Size Scaling of Helical-Core Optical Fibres

The mode-area scaling properties of helical-core optical fibres are numerically studied and the limit of core size for achievable single-mode operation is explored. By appropriate design, helical-core fibres can operate in a single mode with possible scaling up to 300 μm in core diameter with numerical aperture 0.1.