Self-defocusing Material Research Articles

Using Femtosecond Laser Pulses to Explore the Nonlinear Optical Properties of Au NP Colloids That Were Synthesized by Laser Ablation.

In this study, we experimentally investigated the nonlinear optical properties of Au nanoparticles (Au NPs) that were prepared in pure distilled water using the laser ablation method. The Au NPs were prepared using a nanosecond Nd:YAG laser with an ablation time of 5 or 10 min at a constant laser energy of 100 mJ. The structure and the linear optical properties of the Au NPs were investigated using a transmission electron microscope (TEM) and UV-visible spectrophotometer analysis, respectively. The TEM measurements showed that the average size of the Au NPs varied from 20.3 to 14.1 nm, depending on the laser ablation time. The z-scan technique was used to investigate the nonlinear refractive index () and nonlinear absorption coefficient () of the Au NPs, which were irradiated at different excitation wavelengths that ranged from 740 to 820 nm and at different average powers that ranged from 0.8 to 1.6 W. The Au NP samples exhibited a reverse saturable absorption (RSA) behavior that increased when the excitation wavelength and/or incident laser power increased. In addition, the Au NPs acted as a self-defocusing material whenever the excitation wavelength or incident power were modified.

Exact solutions for the quintic nonlinear Schrödinger equation with time and space

Using similarity transformations, the analytical solutions to the quintic nonlinear Schrodinger equation with potentials and nonlinearities depending both on time and space are constructed. The stability of resonance solitons is examined by direct numerical simulation. It is found that stable fundamental soliton states with \(m=0\) and low-order soliton states with \(m=1\) can be supported both by self-focusing and self-defocusing materials. Higher-order solitons are found unstable, however, displaying quasi-stable propagation over prolonged distances.

Bright and dark spatial solitons in metallic nanowire arrays

We investigate the formation and propagation of bright and dark three-dimensional unstaggered spatial solitons with cylindrical symmetry in a nonlinear nanowire metamaterial. The metamaterial is formed by metallic nanowires embedded in a Kerr-type dielectric host and is modeled using an effective medium approach. Unlike conventional Kerr media, the metamaterial supports bright solitons when the host is a self-defocusing material and dark solitons when the host is a self-focusing material. Our numerical calculations show that the confinement of the spatial-solitons results from the interplay of the host nonlinear response strength and the hyperbolic dispersion of the photonic states in the nanowire array. Subwavelength solitary beams may be observed for sufficiently strong nonlinearities.

Resonance solitons produced by azimuthal modulation in self-focusing and self-defocusing materials

We demonstrate azimuthally modulated resonance scalar and vector solitons in self-focusing and self-defocusing materials. They are constructed by selecting appropriately self-consistency and reso- nance conditions in a coupled system of multicompo- nent nonlinear Schrodinger equations. In the case with zero modulation depth, it was found that the larger the topological charge, the smaller the intensity of the soliton in the self-focusing material, while in the self- defocusing material the opposite holds. For the soli- tons with the same parameters, the ones in the self- focusing material possess larger optical intensity than the ones in the self-defocusing material. The stabil- ity of resonance solitons is examined by direct nu- merical simulation, which demonstrated that a new class of stable scalar fundamental soliton states with m = 0 and low-order vector vortex soliton states with m = 1 can be supported by self-focusing and self- defocusing materials. Higher-order solitons are found unstable, however, displaying quasi-stable propaga- tion over prolonged distances.

Internal oscillation of necklace solitons in Bessel photonic lattice imprinted in defocusing and focusing materials

Internal modes and internal oscillation of necklace solitons in Bessel photonic lattices imprinted in self-defocusing and self-focusing materials are investigated. Under the same parameters, necklace solitons in self-focusing material possess larger power than that of self-defocusing material, and the stability of solitons in defocusing material is better than in focusing material. It is shown that the internal modes have both real and imaginary parts in such cases, differing from the one-dimensional case. While white noise gives rise to jitter of the intensity of stable necklace solitons, the stable solitons perform long-distance and quasi-periodic oscillation of intensity and shape under the perturbation of internal modes, and the solitons in self-defocusing material experience larger oscillation amplitude than that in self-focusing material.

Experimental demonstration of novel effects on the far-field diffraction patterns of a Gaussian beam in a Kerr medium

We report on the experimental observation of the effects on the far-field patterns obtained when a divergent or convergent beam interacts with a thin self-defocusing material. The measurements were performed using a CW laser beam propagated through a cell containing a colloidal system that presents a very large nonlinear refractive index. The high nonlinearity of the colloid allowed for the observation of patterns never investigated before, revealing a quite different behaviour on the far field from a convergent or a divergent beam due to the opposite interaction with the negative Kerr nonlinearity of the medium. An unpredicted relation between the number of generated rings and the nonlinear phase-shift is obtained in the case of a convergent beam. Our results are in good agreement with a model for thin nonlinear media.

Variable coupling coefficient nonlinear directional couplers with self-focusing and self-defocusing nonlinearity.

Nonlinear directional couplers (NLDCs) with a variable coupling coefficient (VCC) in self-focusing and self-defocusing materials are investigated. Specifically, the Gaussian type VCC NLDCs are studied in detail. The results show that the responses of the VCC NLDCs on self-focusing and self-defocusing materials are different, especially when input power is high. The coupled-mode theory can also be used to predict the characteristics of the VCC NLDC on self-focusing material, even when input power is high.

Solitonlike pulses in self-defocusing AlGaAs waveguides

We present experimental results showing the existence of bright temporal solitonlike pulses in a self-defocusing material with normal dispersion. Operating close to the fundamental absorption edge of an AlGaAs quantum-well waveguide, we observed narrowing of both the spectrum and the temporal width of the pulses. Two-photon absorption also influenced the propagation of these pulses, and its effects are described.

New Self-Defocusing Materials: Synthesis, Structures and Nonlinear Optical Properties of Nest Shaped Clusters

AbstractMixed metal clusters (n-Bu4N)2[MoCu3OS3X3] (X = SCN, Cl and Br) were synthesized by solid state reactions. X-ray single crystal diffraction data show that the anionic clusters assume nest shaped structures. The clusters exhibit large self-defocusing effect as demonstrated by their Z-scan traces. The effective third-order polarizability of |γ| = 4.8 × 10−29 esu was determined for (n-Bu4N)2[MoCu3OS3(SCN)3] by a degenerate four-wave mixing technique with 7-ns laser pulses of 532 nm wavelength. An irradiance-dependent transmission measurement was conducted to assess the contribution of nonlinear absorption to the γ-value. These results in combination with the self-defocusing property of the cluster yielded a negative value for the real part of γ, Reγ = − 4.8 × 10−29 esu. These numerical values are in good agreement with those obtained in a Z-scan experiment. Even though the clusters absorb laser light at 532 nm significantly, the results of temporal profile analysis on transmitted pulses show that the solvent thermal effect makes little contribution to the observed nonlinear optical phenomenon.

Stability of fundamental nonlinear guided waves

We determine the stability of nonlinear guided waves, including solitons, nonlinear surface waves, and modes of nonlinear waveguides, by simply reading the familiar dispersion diagram without further calculation. The waveguide can be of arbitrary cross section and arbitrary profile shape and can be composed of arbitrary nonlinear materials distributed nonuniformly. This criterion is the first to our knowledge that is universal for the long-standing problem of stability of fundamental nonlinear guided waves, i.e., waves without nodes. We also show that the transverse stability of planar nonlinear guided fundamental waves demands that the material be self-defocusing in at least some portion of space, whereas planar black solitons are unstable in arbitrary self-defocusing material.

Spatial Dark-Soliton Stripes and Grids in Self-Defocusing Materials

Spatial Dark-Soliton Stripes and Grids in Self-Defocusing Materials

Spatial dark-soliton stripes and grids in self-defocusing materials.

Spatial dark-soliton (SDS) stripes are experimentally found in the transverse plane of a laser beam that passes through a rectilinear diffraction screen before propagating in a self-defocusing nonlinear material. Materials with different mechanisms of nonlinearity manifest the same qualitative results. The SDS nature of the observed phenomenon is verified by numerical simulations of the (2+1)-D nonlinear Schr\odinger equation, analytical solutions for the (1+1)-D case, and their comparison with experimental data.

Instabilities and all-optical phase-controlled switching in a nonlinear directional coherent coupler

The instability in the evolution of a nonlinear wave along a directional coupler is investigated with the beam propagation method, both for self-focusing and for self-defocusing materials. A new device is proposed for switching an intense light beam at the device output by changing the relative phase of a weak input signal.