Journal of Nonlinear Optical Physics & Materials

A series of mono-substituted pyrene derivatives having a pyrene mesogenic core and aldehyde group peripherals were designed and synthesized, which had typical D-$\pi$-A structures. Photophysical properties of the compounds were characterized by UV/Vis spectroscopy and the third-order nonlinearities of the compounds were studied by “open aperture” and “closed aperture” $Z$-scan techniques. Both of the compounds showed typical nonlinear absorptions and refractions, and the third-order nonlinear susceptibilities have been found to be very high in all cases. The significant nonlinear optical response combined with the possibility to further modify it, by changing the electron acceptor and the electron-donor groups, suggests that these systems can prove to be important candidates for a variety of photonic/optoelectronic applications.

In this paper, we investigated the angular behavior of light transmission through opal films over a broad range of wavelengths and angles. The opal films were prepared using the capillary deposition method (CDM). The observation of many well-defined diffraction peaks indicates that the CDM results in opal films with high quality. Peaks overlapping at normal incidence split when samples are rotated. The angular shift of these peaks was found to satisfy the kinematical diffraction theory very well. Furthermore, the variation of intensity with incident angle can be interpreted in terms of a simplified dynamical diffraction theory. Moreover, the presence of two differently oriented domains in CDM-made opal films is essential in discussing the measured spectra. These domains can be assigned to parallel microscopic stripes of ABC and ACB type fcc structures. Angular-resolved spectroscopy with polarized incident light shows interesting polarization dependence of light propagation inside opals.

Nonlinear optical properties of a two-level molecular system immersed in a thermal bath have been studied in the present work. Solvent effects were explicitly considered by modeling the non-radiative interaction with the solute as a random variable. The innovation of this treatment is that it allows us to take into account the environment, inducing quantum effects not considered by classical treatment. The major contribution of the methodology proposed in this work, is the implementation of an approximant to the Voigt function as a probability distribution, because it allow us to cover a wider range of possible interactions among the solvent and the molecular system by simple changing the parameters ${\sigma }_L$ and ${\sigma }_G$, associated to the variances of the Lorentzian and Gaussian distributions, respectively.

In the present study, L-alanine crystal is grown with cobalt chloride as dopant by low temperature solution growth using slow evaporation technique at room temperature. The lattice parameters of the grown pure and cobalt chloride doped L-alanine crystals were determined by the single crystal X-ray diffraction technique. The presence of the elemental composition such as cobalt chloride present in the L-alanine lattice was confirmed by energy dispersive X-ray analysis. The optical transmittance, absorbance, reflectance was measured and used to study the optical properties of the pure and doped L-alanine crystal. The pure L-alanine crystal has high optical transmittance in the whole visible range and UV transparency with lower cutoff wavelength at 240nm. By adding cobalt chloride to L-alanine crystal, the transmittance decreases the value of cutoff shifts to the higher wavelengths. Nonlinear optical studies reveal that the SHG efficiency and laser damage threshold energy increases when the L-alanine crystal is doped with cobalt chloride. From microhardness studies, it is observed that the cobalt chloride doped L-alanine crystal is harder than the pure crystal.

Here, we theoretically suggest the possibility of optical nonlinear enhancement by employing the binary optimization of plasmonic nano-bi-domes. Since the nonlinear coefficient depends strongly on the number of plasmonic nanoparticles and the nanoparticles location, binary particle swarm optimization (BPSO) algorithm is proposed to design an optimized array of the plasmonic nano-bi-domes in order to achieve the maximum nonlinear coefficient in the optical frequency. In BPSO, a swarm consists of a matrix with binary entries, control the presence (‘1’) or the absence (‘0’) of nano-bi-domes in the array. It is shown that the interaction between six nano-bi-domes leads to a very strong amplification of the Electro Magnetic (EM) fields inside and in the near-field range outside the particles. Correspondingly, such systems exhibit strong resonance peaks in the nonlinear coefficient spectrum.

Nanoparticles of Titanium dioxide $({\mathrm{\text{TiO}}}_2)$ with its unique optical and electronic characteristics is an important material for photochemical catalysis. The efficiency of catalytic activity of ${\mathrm{\text{TiO}}}_2$ anatase nanostructures is greatly influenced by the photo-generated bound excitons. It is found that the interaction of bound excitons generated in ${\mathrm{\text{TiO}}}_2$ enhances the cubic nonlinearity of the system due to strong oscillation of photo-generated bound excitons. The trapped electron hole pair concentration is directly proportional to the photocatalytic efficiency of the ${\mathrm{\text{TiO}}}_2$ anatase nanostructures. In our report, we show how these photo-generated bound excitons play a significant role in origin of third-order optical nonlinearities. In particular, we have measured large phase shift and seen two photon absorption process through closed and open aperture Z-scan, respectively, using femtosecond pulses at 532nm.

The newly introduced imaging Dark-field Z-scan (DFZ-scan) technique is applied here to demonstrate its ability to measure the optical third-order nonlinear (NL) index coefficient in the presence of nonlinear absorption (NLA). We present our experimental results for two compounds of Porphyrin molecules, known to have relatively high NLA in the picosecond regime, at 532nm, allowing to test both cases of positive and negative nonlinear refraction (NLR). Moreover, we show that, it is possible to increase the sensitivity of the method by introducing a circular aperture in the image plane. Also, limitations are discussed to process optically a pure NL refractive signal, not subject to the influence of the NLA one, at the output of the imaging setup.

This paper is concerned with non-autonomous Maxwell–Bloch equations when subject to a time delay. We investigate the dynamical behavior of an optical bistable system for inhomogeneous Lorentzian broadening and transverse Gaussian field effects interacting with a single mode ring cavity both inside and outside the rotating wave approximation. Results show that the known bistable behavior of the device can be affected by instabilities. However, in some cases, for instance, when the incident Gaussian laser beam waist is less than that of cylindrical atomic sample, a large butterfly hysteresis is demonstrated in the fundamental field component. As far as the authors are aware, this is the first time that such behavior has been demonstrated.

This paper describes experimental results of thermal diffusivity measurements performed on different concentrations of aqueous Tartrazine solutions. The measurements are performed using the frequency-resolved thermal lensing technique and the results are compared with the thermal diffusivity value of pure water used as a solvent or host liquid. The results show that at low concentrations, the thermal properties of the solution are roughly equal to those of the water. However, when the concentration is increased, the thermal properties of the solutions diverge from that of the host liquid.

A photonic crystal fiber (PCF) with a zero-dispersion wavelength (ZDW) in the telecommunication region is designed and an ultra-broadband fiber optical parametric amplifier (FOPA) based on such PCF is simulated. Results show that the PCF-based FOPA exhibits much higher gain with a very broad bandwidth (covering O- to U-band) in comparison with the highly nonlinear fiber (HNLF)-based FOPA. Also, the required fiber length and the input pump power are reduced for the PCF-based FOPA. The obtained results show the great potential of the PCF-based OPA for the telecommunication applications, e.g. amplification of wavelength-division multiplexing (WDM) signals.

This paper reports the simulation of L-band multi-wavelength Brillouin–erbium fiber laser that utilizes delay interferometer as a comb filter. The simulation is performed using OptiSystem. The structure exhibits threshold power in terms of Erbium doped fiber amplifier (EDFA) gain of 10mW at a very low Brillouin pump power of 0.00316mW for the generation of first Stokes. Thirty one output channels were produced with minimum EDFA gain of 1W at Brillouin pump power of 0.00316mW. In line with theory, it has been observed that higher Brillouin pump power requires low threshold gain and vice versa to generate the Brillouin Stokes.

We demonstrate a Q-switched Erbium-doped fiber laser (EDFL) using a molybdenum disulfide (MoS${}_2)$-based saturable absorber (SA) as a Q-switcher. The SA is prepared from commercial available MoS₂ pristine flakes with final solution concentration of $\sim$0.02mg/ml. The Q-switcher is assembled by depositing a dried MoS₂ onto a fiber ferule facet before it is matched with another clean ferrule via a connector. By increasing the pump power from 120mW to 160mW, stable generation of Q-switched EDFL incorporating MoS₂ SA has been obtained at 1502nm wavelength. The pulse repetition rate also varies from 45.2kHz to 66.0kHz with pulse width which is increased from 2.73$\mu$s to 3.19$\mu$s. At pump power of 160mW, we successfully generated the maximum average output power of 0.51mW, corresponding to a pulse energy of 7.8nJ.

A one-dimensional linear waveguide array with a parity-time($\mathcal{𝒫}\mathcal{𝒯}$)-symmetric defect, which is represented by a pair of waveguides carrying equal amount of nonlinear gain and loss, is considered. Compared to the system with linear $\mathcal{𝒫}\mathcal{𝒯}$-symmetric defect, a different instability of solitons is exhibited in this model, in which the unstable fundamental discrete solitons suffer either decay or blowup. The effect of nonlinear $\mathcal{𝒫}\mathcal{𝒯}$-symmetry on the stability of fundamental solitons is investigated numerically by obtaining the stability region of the solitons. The region has a finite threshold of total power as the coupling within the defect is less than the counterpart of other linear waveguides, while the threshold is absent as the coupling within the defect is larger than the one between other linear waveguides. The stability region is intensely enlarged by the increase of the coupling strength within the defect, and descends exponentially with the increase of the total power.