Ti3AlC2 coated D-shaped fiber saturable absorber for Q-switched pulse generation

In this letter, a titanium aluminum carbide (Ti3AlC2) coated D-shaped fiber is proposed and demonstrated as a new saturable absorber (SA) for Q-switched laser pulse generation. In preparing the SA, the Ti3AlC2 powder is dispersed in liquid polyvinyl alcohol (PVA) before the solution is dropped and left to dry onto a polished surface of D-shape fiber. The SA is added to an erbium-doped fiber laser (EDFL) cavity to modulate the cavity loss for Q-switching. The Q-switched laser is obtained at 1 561 nm. The pulse width of the pulses can be varied between 7.4 µs and 5.1 µs with a corresponding repetition rate range from 41.26 kHz to 54.35 kHz, when the pump power is increased from 42.2 mW to 71.5 mW. At 71.5 mW pump, the pulse energy is obtained at 70.3 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is recorded at 67 dB, which indicates the stability of the laser.     

Polymer-metal complexes,based on poly(itaconic acid ester) derivatives,as catalysts for the decomposition of hydrogen peroxide

Poly(methyl itaconates) and poly(heptyl itaconates), modified with ethylene diamine (EN) and tetraethylene pentamine (TETRAEN) side chains, were complexed with cobalt and copper ions, and their efficiencies as catalysts for the decomposition of hydrogen peroxide were assessed. All the polymer complexes studied were found to be active catalysts, but it was observed that the polymers with TETRAEN side chain, when complexed with CoCl₂ and CuCl₂ were less efficient than polymers with EN side chains which were complexed with trans-dichlorobis(ethylenediamine) cobalt(III) chloride, trans-[Co(EN)₂Cl₂]Cl. One feature of interest was that when the alkyl side chain of the poly itaconate was heptyl the rate of decomposition of hydrogen peroxide was faster than when the alkyl group was methyl.     

Tunable dual-wavelength thulium-doped fiber laser at 1.8 μm region using spatial-mode beating

This study describes a proposal and experimental demonstration of a tunable thulium-doped fiber laser with a multi-wavelength output operating at 1.8 μm. The introduction of a multi-mode non-adiabatic taper fiber into a single-mode cavity induces spatial-mode beating and a consequent narrow band filter mechanism. The fiber laser can be tuned by changing the state of the polarization in a ring cavity via adjustment of a polarization controller. The resulting outputs for single and dual wavelengths with different spacing are reported in detail.     

Enhanced hybrid image security algorithms for high definition images in multiple applications

Protection of multimedia information from different types of attackers has become important for people and governments. A high definition image has a large amount of data, and thus, keeping it secret is difficult. Another challenge that security algorithms must face with respect to high definition images in medical and remote sensing applications is pattern appearances, which results from existing regions with high density in the same color, such as background regions. An encryption and hiding based new hybrid image security systems are proposed in this paper for the purpose of keeping high definition images secret. First, one hiding method and two encryption methods are used in two hybrid algorithms. The new hiding algorithm proposed here starts by applying reordering and scrambling operations to the six Most Significant Bit planes of the secret image, and then, it hides them in an unknown scene cover image using adding or subtracting operations. Second, two different ciphering algorithms are used to encrypt the stego-image to obtain two different hybrid image security systems. The first encryption algorithm is based on binary code decomposition, while the second algorithm is a modification of an advanced encryption standard. After evaluating each hybrid algorithm alone, a comparison between the two hybrid systems is introduced to determine the best system. Several parameters were used for the performance, including the visual scene, histogram analysis, entropy, security analysis, and execution time.

     

Applied whispering gallery modes on ZnO nanorods coated glass for humidity sensing application

In this letter, a humidity sensor is demonstrated by applying a whispering gallery mode (WGM) from a microsphere resonator onto the ZnO nanorods coated glass surface. The diameter of the microsphere was 234 µm and the glass surface was coated with ZnO nanorods using the hydrothermal method at growth duration of 12 h. A significant response to humidity level ranging from 35%RH to 85%RH has been observed with the sensitivity of 0.014 2 nm/%RH. The proposed humidity sensor has successfully employed to enhance interaction between the whispering gallery mode evanescent and surrounds analyte with the assistance of ZnO nanorods coated glass.     

Gold nanoparticles film for Q-switched pulse generation in thulium doped fiber laser cavity

Passively Q-switched thulium doped fiber laser (TDFL) has been successfully demonstrated using gold nanoparticles (GNPs), which were embedded into polyvinyl alcohol as saturable absorber (SA). The stable self-starting Q-switched laser was generated to operate at 1 891 nm when a tiny piece of the prepared film was slot in between two fiber ferrules and incorporated into the laser cavity. The repetition rate can be adjusted from 48.54 kHz to 49.64 kHz while the pulse width decreased from 3.52 μs to 2.38 μs with the increase of 1 550 nm pump power from 840 mW to 930 mW. The corresponding pump power output power linearly increased from 3.62 mW to 6.3 mW with a slope efficiency of 2.53%. The maximum peak power and pulse energy were recorded at about 39 mW and 0.12 µJ, respectively at pump power of 930 mW. The Q-switching operation was caused by the surface plasmon resonance absorption of GNPs.     

Vanadium pentoxide film for microsecond pulse generation in 1.5-μm region

Q-switched erbium doped fiber laser (EDFL) was passively realized using vanadium pentoxide (V2O5) embedded into polyethylene glycol (PEG) film as saturable absorber (SA). The laser could successfully generate stable self-starting pulses when the V2O5 film was placed in an EDFL cavity. It operated at 1 562.4 nm wavelength. The repetition rate can be varied from 91.7 kHz to 128.2 kHz while the pulse width shrank from 10.90 μs to 7.81 μs with rising pump power from 110.9 mW to 166.5 mW. The pulse energy recorded was 3.2 nJ at pump power of 166.5 mW. The results indicate that the saturable absorption of V2O5 has promising nonlinear photonic applications especially in fiber laser development for 1.5-μm region.     

Polypropylene/phosphazene nanotube nanocomposites: Thermal,mechanical, and flame retardation studies

In this study, flame retardant polypropylene (PP) nanocomposites with superior mechanical performance have been developed using amine-functionalized phosphazene nanotubes (APZS, 1–10 wt%) through melt-blending method. Polypropylene-graft-maleic anhydride was used as the compatibilizer to attain effective interaction between the nanofiller and the PP matrix. The characterization of amine-functionalized phosphazene nanotubes (APZS) using solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy, X-ray diffraction, fourier-transform infrared (FTIR), and transmission electron microscopy indicated successful amine functionalization, though structural changes were observed as compared to the unfunctionalized nanotubes. Owing to the covalent polymer-filler interfacial interactions and resulting in uniform filler dispersion, the nanocomposites exhibited significant enhancement in the tensile modulus up to 5 wt% APZS content (98% increment at 5 wt% content as compared to pure polymer). The addition of a small fraction of APZS (1 wt%) improved the impact strength of the nanocomposite by more than 180%. APZS acted as a weak nucleating agent for PP, thereby leading to enhanced degree of crystallinity (up to 5 wt% APZS content). The thermal stability of the nanocomposites was also enhanced with APZS content. The nanocomposites with 5 and 10 wt% APZS loading exhibited a V0 rating in UL-94 test, indicating that APZS introduced a robust flame retardancy behavior in the PP nanocomposites. The limiting oxygen index values also confirmed the findings from the UL-94 analysis. The developed nanocomposites exhibit high potential of use in a wide range of high temperature applications.     

Targeting Asexual and Sexual Blood Stages of the Human Malaria Parasite P. falciparum with 7-Chloroquinoline-Based 1,2,3-Triazoles

Novel 4-amino-7-chloroquinoline-based 1,2,3-triazole hybrids were synthesised in good yields by Cu^I-catalysed Huisgen 1,3-dipolar cycloaddition reactions of 2-azido-N-(7-chloroquinolin-4-ylaminoalkyl)acetamides with various terminal alkynes. These new hybrids were screened in vitro against asexual blood stages of the chloroquine-sensitive 3D7 strain of P. falciparum. The most active compounds were further screened against asexual and sexual stages (gametocytes) of the chloroquine-resistant RKL-9 strain of P. falciparum. Although all compounds were less potent than chloroquine against the 3D7 strain, the three best compounds were appreciably more active than chloroquine against the RKL-9 strain, displaying IC₅₀ values of <100 nm , with one of them having an IC₅₀ of 2.94 nm . Further, the lead compounds were gametocytocidal with IC₅₀ values in the micromolar range, and were observed to induce morphological deformations in mature gametocytes. Most compounds demonstrated little or no cytotoxicity and exhibited good selectivity indices. The most active compounds represent promising candidates for further evaluation of their schizonticidal and gametocytocidal potential.