A. A. I. Khalil

Titanium plasma spectroscopy studies under double pulse laser excitation

Laser-induced breakdown spectroscopy (LIBS) was applied for parametric studies of titanium (Ti) plasma using single and double pulsed laser excitation scheme. Here a pulsed Nd:YAG laser was employed for generation of laser produced plasma from solid Ti target at ambient pressure. Several ionized titanium lines were recorded in the 312–334 nm UV region. The temporal evolution of plasma parameters such as excitation temperature and electron number density was evaluated. The effect of incident laser irradiance, position of the laser beam focal point with respect to the surface of illumination, single and double laser pulse effect on plasma parameters were also investigated. This study contributes to a better understanding of the LIBS plasma dynamics of the double laser pulse effect on the temporal evolution of various Ti emission lines, the detection sensitivity and the optimal dynamics of plasma for ionized states of Ti. The results demonstrate a faster decay of the continuum and spectral lines and a shorter plasma life time for the double pulse excitation scheme as compared with single laser pulse excitation. For double pulse excitation technique, the emissions of Ti lines intensities are enhanced by a factor of five which could help in the improvement of analytical performance of LIBS technique. In addition, this study proved that to avoid inhomogeneous effects in the laser produced plasma under high laser intensities, short delay times between the incident laser pulse and ICCD gate are required.

Effect of ambient conditions on laser-induced breakdown spectra

The role of different ambient conditions on LIBS signal intensity was investigated for better understanding and performance of LIBS as a quantitative and qualitative analytical technique. For this purpose, the relative LIBS signal intensities were measured for a standard Cr line (520.8 nm) at different gas pressures of Ar, He, and air. The plasma was generated using a Q-switched pulsed Nd:YAG laser having wavelength of 1064 nm and pulse duration of 8 ns. The analysis revealed that the intensities of the spectral atomic Cr line (520.8 nm) were strongly enhanced under the argon environment in 10–40 mbar range. The electron excitation temperature (Te) and number density (ne) were estimated by using a Boltzmann plot and a Stark broadening profile, respectively. For optimum dependence of LIBS, laser energy and pressure dependence was also studied. The electron temperature and number density showed an increase with increase in ambient gas pressure.

A spectroscopic analysis study of graphite using laser technique

Results of single and double pulses (SP- and DP) Q-switch Nd:YAG laser induced breakdown spectroscopy (LIBS) at atmospheric pressure on the structure of graphite target are reported. Various parameters, such as laser energy, placement of the focus with respect to the surface of illumination, and time delay between laser pulse and ICCD camera pulse were used as variables. This study contributes to a better understanding of the LIBS plasma dynamics of the SP- and DP effect by observing the temporal evolution of emission line of graphite. The gate width and the delay time were adjusted to achieve the best possible signal to noise ratio. Electron densities were found from Stark broadening. The temporal behavior of the last one was also estimated. It was found that the electron density for DP of 2 × 20 mJ is higher than that for SP of 40 mJ of the same total energy. The results show a faster decay of continuum, spectral lines, and a shorter plasma life.

Detection of carcinogenic metals in kidney stones using ultraviolet laser-induced breakdown spectroscopy

The UV single-pulsed (SP) laser-induced breakdown spectroscopy (LIBS) system was developed to detect the carcinogenic metals in human kidney stones extracted through the surgical operation. A neodymium yttrium aluminium garnet laser operating at 266 nm wavelength and 20 Hz repetition rate along with a spectrometer interfaced with an intensified CCD (ICCD) was applied for spectral analysis of kidney stones. The ICCD camera shutter was synchronized with the laser-trigger pulse and the effect of laser energy and delay time on LIBS signal intensity was investigated. The experimental parameters were optimized to obtain the LIBS plasma in local thermodynamic equilibrium. Laser energy was varied from 25 to 50 mJ in order to enhance the LIBS signal intensity and attain the best signal to noise ratio. The parametric dependence studies were important to improve the limit of detection of trace amounts of toxic elements present inside stones. The carcinogenic metals detected in kidney stones were chromium, cadmium, lead, zinc, phosphate, and vanadium. The results achieved from LIBS system were also compared with the inductively coupled plasma-mass spectrometry analysis and the concentration detected with both techniques was in very good agreement. The plasma parameters (electron temperature and density) for SP-LIBS system were also studied and their dependence on incident laser energy and delay time was investigated as well.

Laser produced plasma diagnosis of carcinogenic heavy metals in gallstones

Gall bladder cancer [GBC] is a highly fatal malignancy. Geographically, regions of high prevalence of gallstones [GSs] have shown to have higher rates of GBC, which is now a recognized risk factor for GBC. Heavy metal toxicity has also been reported to be associated with GBC. An effort therefore at recognizing and avoiding potential risk factors for GBC occurrence is therefore paramount. It is also known that over time heavy metals can accumulate in the biliary system and hence in GSs. We hereby measured the levels of heavy metals in GSs via a highly sensitive technique using a laser produced plasma by comparing the levels of heavy metals in a 29 year old man to a 65 year old man. For this direct spectral analysis of GSs, a laser produced plasma was created by focusing a 266 nm pulsed UV laser generated by fourth harmonics of a Nd:YAG laser on GS samples. For the first time to the best of our knowledge, the plasma parameters, electron temperature and electron density for the GS matrix were computed from the Boltzmann distribution of the upper energy levels and Stark broadening of selected spectral lines. The determination of plasma parameters is important to satisfy the optically thin plasma (to avoid self-absorption) and obtain local thermodynamic equilibrium (LTE) conditions, which are critical for the quantitative analysis. The heavy metal concentrations of chromium, lead, cadmium, nickel and mercury were determined in two different GS samples by recording the laser induced breakdown spectra (LIBS) and by drawing the calibration curves of the spectral lines of carcinogenic metals like chromium, lead, cadmium, nickel and mercury. The results obtained from LIBS were crosschecked using a standard inductively coupled plasma-mass spectrometer (ICP-MS) technique. The effect of delay time (time between the laser pulse and the ICCD camera gate opening) and laser energy on the intensity of the spectral lines of lead, chromium and calcium was also investigated. The system developed in this study is highly applicable for the rapid analysis of any biological or human tissue samples.

Detection of trace elements in nondegradable organic spent clay waste using optimized dual-pulsed laser induced breakdown spectrometer

The detection of trace elements present in nondegradable organic spent clay waste has been carried out using an optimized dual-pulsed laser induced breakdown spectrometer. The two laser pulses at 1064 and 266 nm were collinearly collimated and focused on the sample surface in order to enhance the signal intensity. The atomic transition lines at 568.8 nm (Na-I), 504.2 nm (Pb-II), 405.8 nm (Pb -I), 443.56 nm (Ca-I), 469.41 nm (S-I), 520.8 nm (Cr-I), 643 nm (Cd-I), and 928.1 nm (Cl-I) were used as marker wavelengths, and the concentrations of 688, 300, 204, 460, and 2440 ppm of Pb, S, Cd, Cr, and Cl, respectively, were detected in the 5% spent clay in the binder. The limits of detection of Pb, S, Cd, Cr, and Cl were estimated to be 6.7, 17.2, 6.5, 5.1, and 14.8 ppm, respectively, from the calibration curve for each element. In order to confirm the reliability of our system, the concentrations of the reported elements detected using our system were compared to the ones obtained with inductively coupled plasma emission spectroscopy and found to be in good agreement.

Alternate Path Method Analysis of RC Structures Using Applied Element Method

Recent research using the Applied Element Method (AEM) shows that the method is efficient in modeling progressive collapse analysis of structures. Recent research on progressive collapse design of structures based on the UFC code shows it can be used in optimizing the design for structures for which the alternate path method is required. This paper demonstrates the efficiency of the use of AEM in progressive collapse analysis of reinforced concrete structures by comparison to results of published experimental tests. A case study based on a typical seven-story reinforced concrete frame commercial building is used to demonstrate the advantages of using the alternate path method in progressive collapse design of concrete structures even for the cases where the code permits the use of the tie force method. The contribution of infill walls in resisting progressive collapse is also studied.

High sensitive detection of nitric oxide using laser induced photoacoustic spectroscopy at 213 nm

Trace level detection of nitric oxide (NO) is of great interest for a wide range of applications such as environment and human health. For this purpose, a high sensitive sensor based photoacoustic spectroscopy (PAS) principle has been developed at our laboratory for detection of NO at very low concentration (ppbV). For optimization of the PAS signal and to achieve higher sensitivity, parametric dependence investigation was carried out where PAS signal dependence on NO gas pressure, cell geometry, buffer gas (Ar, N2, He), and laser pulse energy used three PAS cells developed locally. The best sensitivity achieved with three cells was 41, 11, 20 ppbv, respectively. It is worth reporting that the best PAS signal to noise ratio was achieved by using a cylindrical cell having three acoustic filters and argon as a buffer gas.

Design of a novel circulator for wireless transceivers

A novel three port active circulator is proposed. The proposed circulator is composed of a phase divider with one transistor only, and a special form of Wilkinson power splitter operating as a power combiner. The circulator has been employed in FMCW radar front end with one antenna for both transmission and reception purposes. However, it can be used in other wireless communication transceivers. The circulator is designed and optimized at a center operating frequency of 2.45 GHz. Circulator simulations report good isolations for S12 = -34 dB, S31 = -24 dB, and S13 = -13 dB with superior return losses for S11 = -48 dB, S22 = -25 dB, andS33 = -51 dB.

Tungsten ion source under double-pulse laser ablation system

New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd:YAG laser beams (266+1064 nm) are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laser wavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.