Ahmed Bakry

Detection of contaminants in ore samples using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been applied for the determination of contaminants present in ore samples. The plasma was generated by focusing a pulsed Nd:YAG laser radiation at 1064 nm wavelength on the ore sample collected from one of the open-pit mines located in Saudi Arabia. The concentrations in this ore sample of different elements of environmental significance like Cu, Cr, Ca, Mg, Zn, Ti, Si, Fe and Al were determined by spectral analysis. Parametric dependence for improvement of LIBS sensitivity was carried out. The LIBS results were compared with the results obtained using other analytical techniques such as the inductively coupled plasma emission spectroscopy (ICP-AES). Limits of detection (LOD) of our LIBS system were also calculated for the elements under investigation.

Study of hazardous metals in iron slag waste using laser induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) was applied for quantitative elemental analysis of slag samples collected from a local steel plant using an Nd: YAG laser emitting radiation at 1064 nm wavelength. The concentration of different elements of environmental significance such as cadmium, calcium, sulfur, magnesium, chromium, manganese, titanium, barium, phosphorus and silicon were 44, 2193, 1724,78578, 217260, 22220, 5178, 568, 2805, 77871 were mg Kg− 1, respectively. Optimal experimental conditions for analysis were investigated. The calibration curves were drawn for different elements. The concentrations determined with our Laser-Induced Breakdown Spectrometers were compared with the results obtained using Inductively Coupled Plasma (ICP) emission spectroscopy. Our study demonstrates that LIBS could be highly appropriate for rapid online analysis of iron slag waste. The relative accuracy of our LIBS system for various elements as compared with ICP method is in the range of 0.001 - 0.049 at 2.5% error confidence. Limits of detection (LOD) of our LIBS system were also estimated for the elements noted here. The hazardous effects of some of the trace elements present in iron slag exceeding permissible safe limits are also discussed.

Generation of vortex beam using Bragg reflector waveguide

We demonstrated the generation of vortex beams using a GaAs-based ring-shaped Bragg reflector waveguide functioning as a highly dispersive angular diffraction element for potential applications in integrated mode-multiplexing in a multimode fiber. The polarization measurement of far-field patterns shows the formation of a radially polarized vortex beam. A tunable ring-shaped far-field pattern was demonstrated by tuning the wavelength of coupled light. We also integrated multi-ring vortex beam emitters, demonstrating the possibility of the creation and multiplexing of vortex beams with different orbital momentums.

Enhancing Modulation Bandwidth of Semiconductor Lasers beyond 50 GHz by Strong Optical Feedback for Use in Millimeter-Wave Radio over Fiber Links

We present the modeling on high-speed modulation of semiconductor lasers beyond 50 GHz over a frequency band of 2 GHz by using strong optical feedback (OFB). This ultra high modulation frequency is achieved by adjusting the external-cavity resonance frequency close to the modulation frequency and optimizing strong OFB conditions to achieve stable operation. We show that this optimized strong OFB results in about 20 dB improvement in the link gain of a 55.8 GHz radio over fiber (RoF) link. We also discuss the influence of environmental variations on the simulated modulation characteristics.

Microwave assisted synthesis, spectroscopic studies and non linear optical properties of bis-chromophores

Bis chromophores were synthesized by the terephthalaldehyde with (4-nitrophenyl) acetonitrile/(4-flurophenyl) acetonitrile under microwave irradiation. Bis-chromophores were obtained in good to excellent yields. The structures of bis-chromophores were established by FT-IR, (1)H NMR, (13)C NMR, EI-MS and elemental analyses. Physical chemical properties such as singlet absorption, extinction coefficient, stokes shift, oscillator strength and dipole moment, were investigated by UV-Vis and fluorescence spectroscopy measurements. Further we also measured the nonlinear refractive index and nonlinear absorption coefficients of these compounds using the single beam z-scan technique with a cw argon ion laser at 514.5 nm at different concentrations in DMSO solvent. The third order nonlinear susceptibility was estimated from these measurements and it shows high nonlinearity. The high negative refractive index makes these compounds suitable for optical limiting application.

Enhancing the modulation bandwidth of VCSELs to the millimeter-waveband using strong transverse slow-light feedback

We present modeling on the millimeter (mm)-wave modulation of vertical-cavity surface-emitting laser (VCSEL) with a transverse coupled cavity (TCC). We show that strong slow-light feedback can induce 300% boosting of the modulation bandwidth of the TCC-VCSEL. Also, the strong lateral feedback can induce resonance modulation over passbands centered on frequencies as high as 3.8 times the VCSEL bandwidth. The slow-light feedback is modeled by a time-delay rate equation model that takes into account the multiple round trips as well as the optical loss and phase delay in each round trip in the feedback cavity.

High Frequency Modulation of Transverse-Coupled-Cavity VCSELs for Radio Over Fiber Applications

We demonstrate a high-speed and efficient direct modulation of a novel transverse-coupled-cavity vertical cavity surface emitting laser for radio over fiber applications. A bow-tie joint connection between two oxide apertures results in a leaky traveling wave in the lateral direction between the two cavities. The measured L/I characteristics and lasing spectra demonstrate coherent coupling of the two cavities. The small signal response of the fabricated device shows a large enhancement of over 30 dB in the modulation amplitude at frequencies . The resonantly enhanced modulation response is suitable for efficient narrow-band modulation in the millimeter wave range over 25 GHz far beyond the intrinsic modulation bandwidth of the laser without optical feedback.

Synthesis, linear and nonlinear optical properties of a new dimethine cyanine dye derived from phenothiazine

Dimethine cyanine dye (PTZIS) based on phenothiazine as the core donor and indolium salt as the acceptor has been synthesized and fully characterized. UV-Vis absorption and fluorescence properties of PTZIS were studied in different solvents. Absorption spectra revealed a large bathochromic shift of the intramolecular charge transfer (ICT) absorption band of PTZIS compared with those in the non-halogenated solvents. Also, the optical data of PTZIS showed a large Stokes shift compared with those in the non-halogenated solvents, indicating a great influence on the geometry of the emissive excited state. The nonlinear optical properties of PTZIS in ethanol solution at different concentrations and different laser powers have been studied using the Z-scan technique with a continuous wave (cw) argon ion laser at 514.5 nm. The closed aperture Z-scan data was used to estimate the nonlinear refractive index n2, while the open aperture scan provided the nonlinear absorption coefficient β. The values obtained are relatively very high and vary linearly with concentration.

Compact electro-absorption modulator integrated with vertical-cavity surface-emitting laser for highly efficient millimeter-wave modulation

We demonstrate a compact electro-absorption slow-light modulator laterally-integrated with an 850 nm vertical-cavity surface-emitting laser (VCSEL), which enables highly efficient millimeter-wave modulation. We found a strong leaky travelling wave in the lateral direction between the two cavities via widening the waveguide width with a taper shape. The small signal response of the fabricated device shows a large enhancement of over 55 dB in the modulation amplitude at frequencies beyond 35 GHz; thanks to the photon-photon resonance. A large group index of over 150 in a Bragg reflector waveguide enables the resonance at millimeter wave frequencies for 25 μm long compact modulator. Based on the modeling, we expect a resonant modulation at a higher frequency of 70 GHz. The resonant modulation in a compact slow-light modulator plays a significant key role for high efficient narrow-band modulation in the millimeter wave range far beyond the intrinsic modulation bandwidth of VCSELs.

Synthesis, Spectrofluorometric Studies, Micellization and non Linear Optical Properties of Blue Emitting Quinoline (AMQC) Dye.

Blue emitting 2-amino-4-(3, 4, 5-tri methoxyphenyl)-9-methoxy-5,6 dihydrobenzo[f]isoquinoline-1-carbonitrile (AMQC) dye was synthesized by one-pot multicomponent reactions (MCRs) of 3,4,5-trimethoxybenzaldehyd, malononitrile, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one and ammonium acetate. Results obtained from spectroscopic and elemental analysis of synthesized AMQC was in good agreement with their chemical structures. Fluorescence polarity study demonstrated that AMQC was sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including electronic absorption, excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield were investigated in order to explore the analytical potential of AMQC. Dye undergoes solubilization in different micelles and may be used as a quencher and a probe to determine the critical micelle concentration (CMC) of SDS and CTAB. Nonlinear optical parameters of AMQC dye shows relatively lower nonlinear refractive index and nonlinear absorption coefficient at the power levels. Variation of n2 with concentration is linear in the concentration range used in the present study.