Journal of Nonlinear Optical Physics & Materials

A fiber laser resonantly pumped Q-switched mode locked Er:YAG ceramic 1645 nm laser using graphene as the saturable absorber is realized. The mode-locked pulses with average output power of 320 mW, Q-switching envelope temporal width of 10 μs and mode-locking repetition rate of 83 MHz can readily be generated from the laser. To the best of our knowledge, this is the first report on the graphene-based Q-switching mode locked Er:YAG ceramic laser emitting around 1645 nm.

In this paper, we experimentally demonstrate a stable passive Q-switched fiber laser operating at 1543.5 nm using a double clad Erbium-Ytterbium co-doped fiber (EYDF) as the gain medium in conjunction with nonlinear polarization rotation (NPR) technique. An isolator is used in conjunction with a highly nonlinear EYDF to induce intensity dependent loss in a sufficiently-high loss ring cavity to achieve Q-switched operation with a low pump threshold of 300 mW. At 980 nm multimode pump power of 500 mW, the EYDF laser generates an optical pulse train with a repetition rate of 46.95 kHz, pulse width of 5.3 μs and pulse energy of 75.6 nJ. The simple and inexpensive Q-switched NPR-based laser has a big potential for applications in metrology, environmental sensing and biomedical diagnostics.

In this paper, a micro Doppler shift velocimeter using two nested-microring resonators incorporating two gratings is designed and simulated. Two wavelength light pulse can be generated by a single input wavelength source after travelling through the two defect grating. Whispering gallery mode of light pulses are localized within the nested-microring resonators, which can be used to form the two point probe Doppler shift velocimeter. The shifted frequency (velocity) can be obtained by the difference of optical path length between two point probes, where the relative velocity of Doppler frequency shift velocimeter can be obtained. The light absorption behaviors can also be investigated by the different light output spectrum. The obtained simulation results shows that the relative velocities of the reflection and transmission light intensities are ranged from 10⁴ m/s to 10⁵ m/s, which can be useful for Doppler frequency shift velocimeter and sensors, where the micro-optical device and multi-functions are the advantages.

Mach–Zehnder interferometric technique has been used to calculate the nonlinear refractive index (n₂) of 2, 5-dimethylaniline (DMA) dissolved in methanol. The technique uses the ratio of the measured input powers to the corresponding output powers to estimate the nonlinear phase shift of DMA. Calculated value of the nonlinear refractive index of DMA was fund to be of the order of 10^-6 cm²/W.

Using vis absorption, fluorescence spectral experimental data, and time-resolved measurement, we have examined the kinetics of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate (ZnPc(COONa)₄), which is interesting photosensitizer of far red-absorption in water:NaOH solution. The kinetic parameters were measured and/or calculated. The photophysical properties originate principally from the planar macrocycle while the outer substituent and degree of carboxylation seem not to have a considerable influence on the kinetic parameters. The nonradiative rate constants of the first excited state were dominant due to the heavy metal effect. Using the obtained photophysical parameters, the population dynamics were calculated by kinetic model. On nanosecond scale of 15 ns, about 63% population of the first excited-singlet state is retrieved by the ground state. Whereas, the rest of population are deactivated to the first excited-triplet state. Later on, during about 7 μs starting from the initial decay of the first excited singlet state, the first excited singlet state and the first excited triplet state were completely empty, meanwhile the ground state retrieved its initial population. Due to the fact that ZnPc(COONa)₄ has strong absorption, long lifetimes of the first singlet and triplet excited states, and fast intersystem crossing, it may be suitable for nonlinear optical studies.

This paper obtains bright, dark and singular soliton solutions to dense wavelength division multiplexed (DWDM) system, with spatio-temporal dispersion. There are two types of nonlinear media that are considered and they are Kerr law and parabolic law. Four integration algorithms are applied to retrieve these solitons. They are G′/G-expansion scheme, extended tanh function approach, Kudryashov's algorithm and finally the ansatz method. The results follow with respective constraints that guarantees the existence of solitons.

We illustrate the analytical control of the Akhmediev breather frequency in Bose–Einstein condensate in a time varying parabolic trap. This is achieved by varying Feshbach managed scattering length R(t) within the integrability framework. Recognizing the mathematical relation between R(t) and parabolic trap with the linear Schrödinger equation, we use isospectral Hamiltonian approach, which leads to a one parameter family of nonlinearity control functions, directly affecting the characteristic scales of the solution space, for the same trapping potential. The chirp equation and the trap equation being same, the phase of the wave for the obtained class of nonlinearity function remains identical. For explicating the general applications of the present approach, we exhibit breather frequency control in a number of cases, with asymptotically vanishing nonlinearity, for expulsive parabolic trap. Interestingly, the same procedure is found to provide a free parameter, which controls the Rogue wave amplitude.

We have used single-stranded DNA (ssDNA) and polyvinylpyrrolidone (PVP) to disperse multiwalled carbon nanotubes (MWNTs) in water solution through sonication and centrifuge procedures. The advantage of these two polymers is that they do not need toxic organic solvents to distribute the carbon nanotubes. The scanning electron microscope (SEM) technique has been used to investigate the interaction between polymer molecules and MWNTs. The images show that MWNTs can be distributed effectively into the two polymer solutions. The third-order optical susceptibility, nonlinear optical absorption coefficient and optical power limiting of these dispersions have been characterized experimentally using a femtosecond laser system with a tunable range of 750–850 nm. The imaginary part of the third-order optical susceptibility has also been computed.

Output characteristics of a double-pass singly-resonant optical parametric oscillator (SRO) resonant for both signal and idler waves are investigated as a function of reflectivity of the output coupler based on periodically poled Mg-doped stoichiometric LiTaO₃(PPMgSLT) with a period of 32.7 μm. A configuration of plane-parallel two-mirror cavity is employed and the crystal surfaces are not coated. The SRO was pumped by a Nd:YAG laser which provides 85 ns-long-pulses with a repetition rate of 10 kHz. In our experiment, the wavelengths of signal and idler are 1.98 and 2.3 μm and the maximum available pump power is ~ 21 W. Maximum average powers (conversion efficiency) of the total, the signal and the idler are 12.2 W (59%), 7 W (34%) and 5.6 W (27%), respectively.

In this work, the dynamics of a pulse train propagating through a bimodal optical fiber whose core refractive index varies periodically along its main axis are studied numerically. The mathematical model is based on a coupled system of nonlinear Schrödinger-like equations. First- and second-order dispersions are taken into account, as well as the number of solitons propagating through the fiber. The physical conditions for self-compression of coupled cnoidal waves are obtained and discussed.

This work analyzes the dynamics of two-dimensional spatial solitons in dissipative graded index Kerr media, analytically and numerically. The dynamics of two-dimensional spatial solitons has been studied in a medium with lumped amplification. The presence of lumped amplification in the medium results in the formation of soliton like waves called similaritons. The spatial soliton dynamics has been studied in a dissipative medium. In a dissipative graded index Kerr medium, the balancing between the coefficients of constant dissipation and lumped amplification results in the stabilization of the beam. The beam dynamics has also been studied by varying amplification coefficients with propagation distance. Hyperbolic, linear, and exponential amplification profiles are considered. When amplification coefficient varies with propagation distance, the beam gets compressed. The beam compression is higher in the case of exponential amplification profile than that of hyperbolic and linear amplification profiles.

We consider the nonlinear propagation of an optical beam in a two-dimensional waveguide matrix, which is described by the discrete nonlinear Schrödinger equation with a self-focusing nonlinearity. Our study focuses on the stability domain of the discrete vortex solitons with its topological invariant S equal to 1. Such domain is identified with the propagation constant k and the coupling constant C. Our simulations show that there is a critical value C_cr for any fixed value of k. At C ≤ C_cr, the stable domain is continuous. However, at C > C_cr, the stable domain becomes discontinuous and fuzzy. The distribution of the continuous stable regions is identified and plotted. Moreover, we give the relation of the total power P to C and k, which enable us to figure out the continuous stability area through the (P, C) plane.

The linear and nonlinear optical properties of composite containing aligned prolate spheroid nanoparticles embedded in a dielectric host are studied as a function of depolarization factor. It is shown that the effective third-order nonlinear susceptibility of the composite can be significantly enhanced with respect to the linear optical properties, due to a combination of varying nanoparticle shape and interparticle space. The susceptibility enhancement is up to four orders larger compared to the spherical case. The susceptibility enhancement of the host is finally comparable to the inclusion after choosing property structure parameters. The geometry-dependent susceptibility enhancement can lead to an improved figure of merit for nonlinear absorption.