Journal of Nonlinear Optical Physics & Materials

The first-, second- and third-order nonlinear optical properties of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole in gas phase employing sum-over-states (SOS) method have been calculated for the first time. The ground state molecular structure of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole was obtained by the geometrical optimizations based on the B3LYP/6-31$+$G(d) level. The energy of excited states and transition dipole moments between different excited states were obtained by using the time-dependent density functional theory (TDDFT) based on the CAM-B3LYP/Sadlej POL level. Charge transfer during electron excitation was analyzed based on hole and electron distributions. Our calculations showed that the N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole has good nonlinear optical properties and its nonlinear optical properties arise from charge-transfer excitation and local excitation but charge transfer plays the leading role.

This study deals with numerical simulations to optimize the parameters of the Dark Filed Z-scan (DFZ-scan) in a microscopic configuration for third-order nonlinear (NL) refraction measurements into thin films. The method allows dynamic, transparent, nonlinear phase shifts to be clearly visible. The simulations of such images are obtained for very low-induced refractive indices. Darkfield illumination requires blocking out of the central light which ordinarily passes through and around (surrounding) the NL specimen. A table to approximate circular aperture stop size versus magnification will be given depending on the focusing lens into the tested material.

Effects of spectral diffusion on the third-order nonlinear susceptibility for two- and three-level quantum systems, immersed in a thermal reservoir, are evaluated with a four-wave mixing (FWM) signal through the density matrix formalism. For this, inhomogeneously broadened two- and three-level quantum systems are used. In these models, the distribution of natural frequencies follows a Lorentzian function. The absorptive and dispersive nonlinear optical responses are determined for the considered quantum models. The results presented in this work show potential applications in the development of optical switches and provide a potential method to measure spectral diffusion relaxation times in three-level quantum systems.

We propose and demonstrate a dispersion-independent erbium-doped mode-locked fiber laser by incorporating a chirped fiber Bragg grating (CFBG) into the laser cavity. Our experimental results show that the fiber laser has similar output characteristics, no matter which section of the CFBG is connected to the laser cavity through a circulator, i.e., opposite dispersion is introduced into the laser cavity. Dispersion independent feature is attributed to the relatively large nonlinearity of the laser cavity with certain bandwidth. This enriches the laser dynamics and provides a new idea for the design of new lasers.

Based on the Collins formula in strongly nonlocal nonlinear media (SNNM), the analytical expression for Lorentz beam passing through SNNM has been derived. It is found that the propagation behavior of Lorentz beam is variable and closely related to the parameters of initial ellipticity $p$ and input power. The beam has its own critical power in $x$ and $y$ directions, respectively. If the Lorentz beam with critical power in a certain direction enters in SNNM, its beam width will remain constant in that direction during propagation, otherwise its beam width varies periodically, as either broad or compressed. Moreover, when $p=1$, the beam spot is always symmetrical in $x$ and $y$ directions; when $p\ne 1$, the beam spot is no longer symmetrical in $x$ and $y$ directions. Numerical simulations are carried out to illustrate these quintessential propagation properties.

Investigations were made for optimizing ZnTe as a THz detector at 1560-nm probe beam wavelength, and was compared with its performance at 780nm. High-sensitive THz detection was achieved when phase matching was maintained for long coherence lengths between the probe beam and the incident THz waves. A 1-mm thick ZnTe crystal enabled detection bandwidths of THz radiation up to 2 and 3 THz with probe wavelengths at 1560 and 780nm, respectively. Theoretical calculations showed coherence length of less than 50$\mu$m in ZnTe between the THz wave components above 4 THz and the optical waves at 780 and 1560nm.

The crucial role of nonlinear propagation effects in the self-guiding of femtosecond laser pulses required accurate representation of nonlinearities to describe them. In this paper, an improved theoretical model has been proposed to study the height distribution of the atmospheric nonlinear refractive index. The results show that the revised model obviously improves accurate estimation of nonlinear index at the long wavelength band. Based on the model, we also found the atmospheric nonlinear refractive index differs much from the lower atmosphere to the upper atmosphere. Our results are essential for engineering applications based on the long-distance ultrashort laser pulses’ transmission in diverse atmosphere.

Vector beams with the desired polarization structure interacting with matter result in many novel nonlinear optical effects. Herein, we review the tight focusing and weak focusing properties of three types of light beams, namely, linearly polarized beams, cylindrical vector beams, and hybridly polarized beams. In particular, we revisit the second- and third-order nonlinear optical effects in nonlinear optical media under the excitation of several types of vector beams with the desired polarization distribution. The prospects of their applications in nonlinear optical microscopy and materials characterization are also briefly discussed.

The equations governing nonlinear light beam propagation in nematic liquid crystals form a $(2+1)$-dimensional system consisting of a nonlinear Schrödinger-type equation for the electric field of the wavepacket and an elliptic equation for the reorientational response of the medium. The latter is “nonlocal” in the sense that it is much wider than the size of the beam. Due to these nonlocal, nonlinear features, there are no known general solutions of the nematic equations; hence, approximate methods have been found convenient to analyze nonlinear beam propagation in such media, particularly the approximation of solitary waves as mechanical particles moving in a potential. We review the use of dynamical equations to analyze solitary wave propagation in nematic liquid crystals through a number of examples involving their trajectory control, including comparisons with experimental results from the literature. Finally, we make a few general remarks on the existence and stability of optically self-localized solutions of the nematic equations.

Nonlinear frequency conversion is the important method to get coherent radiation in all-optical waveband. The intentional manipulation of nonlinear harmonic wave, which has some special phase, amplitude, polarization, and so on, is also important to realize all kinds of optical micro-manipulation, optical micro-fabrication, and optical communication in all-optical waveband. There are three methods to manipulate such nonlinear harmonic wave, which are tailoring the functional facet, the structure of crystals, and the structure of the incident light. In this review, we will systematically introduce the fundamental principle and latest advances in this field and summarize the respective characteristics of these three methods.