Papers by Ashraf El-Sherif
IOP Conference Series: Materials Science and Engineering, 2019
A spectroscopy and visual investigation for turbulent swirling flames formed by four-circumferent... more A spectroscopy and visual investigation for turbulent swirling flames formed by four-circumferential swirling turbojet EV in comparison with a two-circumferential swirling air entries configuration burner using hyper spectral camera. The special design of the EV-burner guarantees flame stabilization at the burner exit by a recirculation of hot gases and entrained fresh reactance mixture. A recirculation zone (vortex breakdown) can be generated when a sufficient strong swirling flow exist. The main parameter of combustion diagnostics based on optical devices is the flame itself, whose spectrum is closely related to the process state, as a fingerprint of the instantaneous operational condition, in terms of energetic yield, fuel consumption and pollutants emissions. The hyperspectral imaging technique in the aspect of flame analysis to give a complete description for the flame zones behavior and distribution of reactions through the whole flame. The spectral peaks for issued flames hav...
International Congress on Applications of Lasers & Electro-Optics
Laser Additive Manufacturing (LAM) is a near-net shape manufacturing approach, meaning that the r... more Laser Additive Manufacturing (LAM) is a near-net shape manufacturing approach, meaning that the resulting part geometry can be considerably affected by heat-induced distortions, solidified melt droplets, partially fused powders, and surface modifications induced by the laser tool motion and processing strategy. High-repetition rate femtosecond laser radiation was utilized to improve surface quality of metal parts manufactured by laser additive techniques. Different laser scanning approaches were utilized to increase the ablation efficiency and to improve the surface finish. Processing of 3D-shaped parts made of Ni- and Ti-base superalloys resulted in the reduction of the average surface roughness to a few microns. This approach can be used to post-process parts made of thermally and mechanically sensitive materials, and to attain complex designed shapes with micrometer precision.Laser Additive Manufacturing (LAM) is a near-net shape manufacturing approach, meaning that the resulting part geometry can be considerably affected by heat-induced distortions, solidified melt droplets, partially fused powders, and surface modifications induced by the laser tool motion and processing strategy. High-repetition rate femtosecond laser radiation was utilized to improve surface quality of metal parts manufactured by laser additive techniques. Different laser scanning approaches were utilized to increase the ablation efficiency and to improve the surface finish. Processing of 3D-shaped parts made of Ni- and Ti-base superalloys resulted in the reduction of the average surface roughness to a few microns. This approach can be used to post-process parts made of thermally and mechanically sensitive materials, and to attain complex designed shapes with micrometer precision.
In recent years, a major push was made for the use of novel laser sources in the processing of se... more In recent years, a major push was made for the use of novel laser sources in the processing of semiconductors and other materials used in photovoltaic and IC applications. In addition to a large number of highly automated laser processes already adopted by the industry, more laser-based processing approaches are being developed to improve performance and reduce manufacturing costs. Common semiconductors are transparent in the infrared spectral region. Therefore laser sources operating at mid-IR wavelengths can be successfully utilized to induce material modifications in semiconductor wafers even beyond the laser-incident surface. We present our initial studies of this processing regime utilizing a self-developed nanosecond-pulsed thulium fiber laser emitting at the wavelength 2 µm. Our experimental approach confirmed that morphology changes could be induced not only at the front (laser-incident) surface of the wafer, but also independently at the back surface. We investigated the in...
Optical and Quantum Electronics
We reported a new method for generating a 4 to 25 ms high power acoustic harmonic bursts, reachin... more We reported a new method for generating a 4 to 25 ms high power acoustic harmonic bursts, reaching more than 110 dB Sound Pressure Level (SPL), from the spherical Helmholtz resonators. The method uses Q-switched Nd:YAG laser pulses (wavelength = 1064 nm, pulse width = 6 ns, and energy = 450 mJ) to induce plasma shocks inside an AISI 316L stainless steel cavity. The confined plasma shock produces an acoustic burst of temporal standing waves which are characterized by a wide harmonic bandwidth. The frequency response of the system depends on the geometry of the used Helmholtz resonator as well as the laser wavelength (with constant laser pulse duration and fluence). The experiments reveal the dependence of the odd/even harmonic on laser wavelength. This method is a prospective alternative for the dodecahedron loudspeakers, other sources in ISO and standard audio tests.
Journal of Engineering Science and Military Technologies
Enhanced emission from nano coated titanium target over than that from normal solid one was measu... more Enhanced emission from nano coated titanium target over than that from normal solid one was measured. The plasma was induced from both targets by the interaction of Nd: YAG laser source at a wavelength of 1064 nm. The enhanced signal emission was monitored using the Ti I-spectral lines at 453.32 and 498.17 nm. Another experiment was conducted after addition of a thin layer of 20 nm gold nanoparticles to the surface of bulk titanium. Enhancement factors were found up to twenty folds. The plasma-enhanced emission was attributed to the strong reduction in the plasma ignition threshold by a factor of 40 after adding the layer ofgold nanoparticles. Modeling to explain the origin of the strong reduction to the ignition threshold and enhanced emission is in advance which recommended that there a strong reduction of the thermal diffusion length of the bulk material to the limits of nanomaterial diameter size.
IOP Conference Series: Materials Science and Engineering
A spectroscopy and visual investigation for turbulent swirling flames formed by four-circumferent... more A spectroscopy and visual investigation for turbulent swirling flames formed by four-circumferential swirling turbojet EV in comparison with a two-circumferential swirling air entries configuration burner using hyper spectral camera. The special design of the EV-burner guarantees flame stabilization at the burner exit by a recirculation of hot gases and entrained fresh reactance mixture. A recirculation zone (vortex breakdown) can be generated when a sufficient strong swirling flow exist. The main parameter of combustion diagnostics based on optical devices is the flame itself, whose spectrum is closely related to the process state, as a fingerprint of the instantaneous operational condition, in terms of energetic yield, fuel consumption and pollutants emissions. The hyperspectral imaging technique in the aspect of flame analysis to give a complete description for the flame zones behavior and distribution of reactions through the whole flame. The spectral peaks for issued flames hav...
The International Conference on Mathematics and Engineering Physics
Fourier Domain optical Coherence Tomography (FD-OCT) is used to obtain subsurface cross-sectional... more Fourier Domain optical Coherence Tomography (FD-OCT) is used to obtain subsurface cross-sectional images with micron level resolution by analyzing the interference pattern created by the mixing of light in a Michelson Interferometer FD-OCT systems are able to obtain a direct measurement of the scattering amplitude along a vertical axis within a bulk sample. One exposure provides the complete scattering profile from the surface into the bulk of the sample; this measurement is commonly referred to as an A-scan. Fourier Domain optical Coherence Tomography (FD-OCT) achieves greater sensitivity and higher imaging speed than time domain OCT and has become a powerful tool for biomedical and material application
The International Conference on Mathematics and Engineering Physics
The basic elements of the optical computer mouse (OCM) are; a light emitting diode (LED), image a... more The basic elements of the optical computer mouse (OCM) are; a light emitting diode (LED), image acquisition system (IAS) which acquires images via the lens and a digital signal processor (DSP) to implement the algorithm to determine direction and distance of motion. Here, we describe the light speckles produced from different colour LEDs and laser sources to design and implement a new optical computer mouse. The speckle pattern will be used also to determine the responsivity and velocity of the device relative to the surface it slides on it. The most important and critical property of speckles is their average diameter, which is independent of the type of the surface being illuminated by coherent (He-Ne laser and diode laser) or partially coherent light (LEDs). The average diameter of a speckle pattern is function of the diameter of the illuminated area of the pad surface, the distance between the pad surface and the detector, and the wavelength of the used light. In this work, we replaced the OCM light source by a small powerful coloured LEDs and laser sources and studying the resulting coloured speckle patterns to investigate the effect of different wavelengths and the distance between the pad surface and the detector on the speckle diameters which affects the response of the OCM.
The International Conference on Mathematics and Engineering Physics
It has been shown that tumor cells are resistant to radiation and that increasing tumor oxygen le... more It has been shown that tumor cells are resistant to radiation and that increasing tumor oxygen levels via laser-mediated hyperthermia treatment increases tumor cell radio sensitivity. Hence, studies of the effects of laser irradiation on tumor oxygen levels are of great interest, as they allow for the optimization of hyperthermia treatment.
The International Conference on Mathematics and Engineering Physics
Optical imaging systems are widely used in different applications include tracking for portable s... more Optical imaging systems are widely used in different applications include tracking for portable scanners; input pointing devices for laptop computers, cell phones, and cameras, fingerprint-identification scanners, optical navigation for target tracking, and in optical computer mouse. We presented an experimental work to measure and analyze the laser speckle pattern (LSP) produced from different optical sources (i.e. various color LEDs, 3 mW diode laser, and 10mW He-Ne laser) with different produced operating surfaces (Gabor hologram diffusers), and how they affects the performance of the optical imaging systems; speckle size and signalto-noise ratio (signal is represented by the patches of the speckles that contain or carry information, and noise is represented by the whole remaining part of the selected image). The theoretical and experimental studies of the colorimetry (color correction is done in the color images captured by the optical imaging system to produce realistic color images which contains most of the information in the image by calculating the RGB components) for the used optical sources are investigated and introduced to present the relations between the signal-to-noise ratios with different diffusers for each light source. From the experimental results, we found that the speckle size ranged from 4.59 to 4.62 m, which are slightly different or approximately the same for all produced diffusers. But, the calculated value of signal-to-noise ratio takes different values ranged from 0.69 to 0.92 for different diffuser, which means that surface texture will affects the performance of optical sensor based on laser speckle pattern used for optical imaging system.
The International Conference on Mathematics and Engineering Physics
A complete characterization and comparison of thermal effect between two high power fiber coupled... more A complete characterization and comparison of thermal effect between two high power fiber coupled diode laser modules operating at wavelengths of 808 nm and 975 nm. For the diode laser to operate at certain wavelength, the internal construction and the used material inside the diode must be different. Both wavelengths have a wide use in the laser design such as pumping another active medium to be lase at a new wavelength, 808 nm used to excite solid state lasers such as Nd:YVO and 975 nm used to excite fiber laser such as Yb fiber laser and Er-Yb fiber lasers, and also in applications in several fields such as military, industrial and biomedical engineering fields. For the 808 nm diode laser the output wavelength varied with changing the temperature while the 975 nm has a very large stability against the change of the operating temperature. We obtained an optical power up to 6 Watt (cw). The electrical characterization of the diode laser modules was examined by measuring the dependence of the laser driving current on the operating voltage. The optical characterization was investigated at different temperatures. These included the laser output power versus the driving current, the output optical power versus electrical input power, the laser output spectrum, the laser beam profile and the dependence of the output power on the temperature. The measured diode laser of 975 nm parameters at 25 o C were (0.3A) threshold current, (35.84%) overall slope efficiency and (975.34 nm) central wavelength with line width of (1.3 nm) at FWHM. The variation of the output power, spectrum with temperature are presented. The measured diode laser of 808 nm parameters at 25 o C were (1.3A) threshold current, (42%) overall slope efficiency and (807.96nm) central wavelength with line width of (3.59nm) at FWHM. The variation of the above mentioned parameters with temperature are presented 1,
The International Conference on Mathematics and Engineering Physics
The basic mechanisms leading to combustion oscillations is in the presence of pressure waves, the... more The basic mechanisms leading to combustion oscillations is in the presence of pressure waves, the flow features large scale motions which drive the instability. The dynamics of the flame is then dominated by processes of hydrodynamic instability, vortex roll-up, vortex interactions, front and reacting stream pulsations, periodic extinctions and resignations, self-acceleration. Combustion instabilities are a major problem in the design of high performance propulsion systems (rocket motors, jet engine afterburners, ramjets). Instabilities are also observed in power plants and in various industrial processes. They are characterized by large oscillations of the flow parameters, which have many undesirable effects. Low frequency oscillations induce large mechanical vibrations in the system, including the combustion chamber, the feeding lines and the connected rotating machinery. Unstable operation enhances, the heat transfer rates at the combustor walls and in extreme cases this may lead to serious damage and even a total loss of the system. The present work investigates the changes induced by pilot injections in the acoustic signature of a newly designed 4slot EV burner using pilot injector at reacting and nonreacting conditions. These changes are affecting the flame stabilization especially in the lean premixed combustion due to the large structures resulting from vortex breakdown and the swirling shear-layers. Pilot injector offered good results in flame stability. The injector position influences the flow field and in turns the flame stability. Different pilot injector fuel shift inside the burner are tested. All the results are to be compared with those obtained by the previously developed 2-slot and 4-slot configuration without pilot injector. This allows the identification of the merits and/or drawbacks of both designs.
The International Conference on Mathematics and Engineering Physics
A diode pumped acousto-optic Q-Switching Er 3+ :Yb 3+ co-doped single mode TEM 00 high power fibe... more A diode pumped acousto-optic Q-Switching Er 3+ :Yb 3+ co-doped single mode TEM 00 high power fiber laser has been reported, laser output average power in excess of 1.65 W was achieved for Qswitching at high repetition rates from 10 kHz to100 kHz. The shortest pulse duration obtained was 10 ns, giving a highest peak power of 9.8 kW and 98µJ energy per pulse, is the highest yet reported from any type of active Q-switched flower double clad fiber laser operating in low order mode. The pulse train with high pulse-to-pulse stability of 95% occurred at a range of high repetition rates up to100kHz with peak power of 0.4 kW, 40ns pulse width and 16µJ energy per pulse at 1550 nm for a launched pump power of 5W.Optical chopper Q-switching technique for Er 3+ :Yb 3+ co-doped fiber laser has been investigated, it was found that the narrowest pulse width of 35 ns with peak power of 15.5kW and energy per pulse 0.5mJ at pulse repetition frequency of 1 kHz. The pulse-to-pulse stability was moderate of 75% occurred at a range of high repetition rates. A comparison between optical chopper Q-switching technique and acousto-optic Q-switching has been done at repetition rate of 20 kHz, the reported high energy per pulse, pulse width and the average power of an optical chopper Q-switching technique are greater than that of acousto-optic Q-switching but the pulse width is narrower and so the high peak power of an acousto-optic Q-switching pulse is greater than that of optical chopper Q-switching technique at high repetition rates of up to 100 kHz.
The International Conference on Mathematics and Engineering Physics
This paper presents the use of an improved laser shadowgraphy method for measuring the dynamic el... more This paper presents the use of an improved laser shadowgraphy method for measuring the dynamic elastic moduli of tungsten, from room temperature to near melting point. The method is based on measuring the frequency of impulse induced longitudinal vibration of a tungsten filament, subject to joule heating. The natural resonance frequency of the filament is obtained by lock-in synchronous photo-detection of the laser generated filament shadowgraph. The correlation between the filament natural frequency and its temperature lead to the calculation of shear modulus at variable temperatures, the tensile and bulk modului of tungsten. The results were compared to those obtained by laser Doppler vibrometry of a tungsten wire induced by pulsed current technique. Our method permitted a wider measuring temperature range and an easier calculation procedure. The used setup was simple, non-destructive, non-contacting and accurate, enabling low cost vibrometry measurements that help in future synthesis and test of new grades of refractory materials, deployed as plasma facing material in the latest fusion reactor or super alloys in critical applications.
The International Conference on Mathematics and Engineering Physics
This paper discusses a newlaser shadowgraphymethodfor investigating the in-plane vibration of ref... more This paper discusses a newlaser shadowgraphymethodfor investigating the in-plane vibration of refractory solid objects at incandescent temperatures.The method is applied whenever the use of Doppler laser vibrometer is inefficient due to small dimensions, high luminosity and poor reflectivity of the test object. We designed an experimental setup that included a modulatedlaser to backlight the vibrating object and to generate an analogue shadowgraph,a photo-detector installed in front of the shadowgraph, isconnected to a lock-in amplifier, and synchronized by the laser modulator,to retrieve the vibration signal from the noisy optical background. The methodwasapplied successfully to detect the resonance frequency of tungsten filament atincandescencetemperature inside an automotive lamp as a proof of concept. This method can be also adapted to test the thermo-elastic characteristics of refractory alloy samples,the mechanical properties of high temperature refractory MEMS lightingsandnano-structured tungsten based advanced thermal shock-resistant lighting sources.
The International Conference on Mathematics and Engineering Physics
Today's gas turbine technology is established in a wide range of applications, including (i) the ... more Today's gas turbine technology is established in a wide range of applications, including (i) the production of electrical power, (ii) thrust generation in turbojets and (iii) driving large size pumps and compressors. The greatest advantages of gas turbines against other prime mover systems e.g. steam turbine systems and piston engine systems, lie in its higher specific power, compact design and low initial costs based on power output. A major problem in gas turbine combustors is combustion instabilities which may cause many undesirable effects including; (a) increased noise levels, (b) oscillating thrust, (c) mechanical vibration that may lead to serious damage and even total loss of the system. These instabilities are characterized by large oscillations of the flow parameters, which in many circumstances may result in the inability of the combustion process to sustain these large oscillations; leading to partial or total flame blow-off. These combustion oscillations could, however be desirable as in pulsed combustors; as it enhance combustion intensity, increase thermal efficiency and reduce the emission of pollutants like NOx, CO and soot. In light of the above mentioned concepts, the present study is directed towards extending the previous studies on the recently introduced turbojet EV burner having twocircumferential swirling entry air passages by a fourcircumferential swirling air entries configuration. This burner design concept appears to offer many advantages, including: The replacement of the traditional fixed vane swirler by circumferential swirling air passages; and hence not only minimizes blockage and allows prior premixing of fuel and air within the conically shaped entry section to the combustor but also eliminates possible risk in case of swirler blade damage. The study is an experimental investigations of the acoustic signature of a newly designed 4-slot EV burner. All the results are to be compared with those obtained by the previously developed 2-slot configuration. This allows the identification of the merits and/or drawbacks of both designs.
The International Conference on Mathematics and Engineering Physics
Fiber lasers technology has grown rapidly due to the rapid advances in high power diodes, diode-t... more Fiber lasers technology has grown rapidly due to the rapid advances in high power diodes, diode-to-fiber coupling schemes and doped fiber design and fabrication. Erbium-Ytterbium (Er 3+ /Yb 3+) co-doped fiber is an attractive active medium for the fiber lasers in which Ytterbium is co-doped with Erbium to produce a spectrum in third telecoms window around 1550nm which makes them suitable sources for long range applications. In this paper the Er 3+ /Yb 3+ fiber laser pumped by a laser diode at 980 nm is simulated using the Optiwave software. The pump source was swept from 1.25 to 5 w to extract the slope efficiency. The pump radiation was focused into the Er 3+ /Yb 3+ fiber through an input mirror, which was 98% reflecting at 1550 nm and 99% transmitting at 980 nm. A length of 0.1 m of Er 3+ /Yb 3+ fiber was used with an N.A. of 0.22, Er 3+ ion density of 25.4 x 10 24 m-3 , and Yb 3+ ion density of 320 x 10 24 m-3. The output mirror was 50% reflecting at 1550 nm. Then the length of the fiber was swept from 1m to 5m in order to obtain optimized fiber length. The simulation results demonstrated that a laser output power of 0.8 W was obtained at 1550 nm for a launched power of 2 W with a slope efficiency of 40% and a lasing threshold of 0.4 W of launched pump power. The results also showed that the optimized fiber length was achieved at 2 m which is in a good agreement with the published similar experimental schemes.
The International Conference on Mathematics and Engineering Physics
EPDM rubbers loaded with different concentration of azodicarbonamide as a foaming agent using two... more EPDM rubbers loaded with different concentration of azodicarbonamide as a foaming agent using two different cross-linking systems were subjected to the mechanical, compression and swelling tests at room temperature (300°K). Samples vulcanized by peroxide reveal more advantage over that vulcanized by sulfur especially for the amount of specific gravity and the compression test. The tensile test shows a noticeable increase in the true stress and strain at break for the sulfur cross-linking system than the peroxide one. For the swelling test, the empirical equation used by Kumnuantip and Sombatsompop shows the best fitting for the degree of swellingtime data.
The International Conference on Mathematics and Engineering Physics
Detection of material ingredients is the main goal of the Laser-Induced Breakdown Spectroscopy (L... more Detection of material ingredients is the main goal of the Laser-Induced Breakdown Spectroscopy (LIBS) technique. However, the light signal from the very little elemental concentration is small enough to produce large errors (relatively large limit of detection LOD). In order to enhance the light signal (spectral radiance) from the very small impurity concentrations, we suggested the addition of drops of gold nanoparticles (NPs) solution on the surface of metallic titanium in what is called nanoparticle-enhanced laser induced breakdown spectroscopy (NELIBS). The radiation from Nd:YAG pulsed laser at 1064 nm was used to irradiate the surface of titanium before and after the addition of nano-gold layer at an energy range from 60 mJ to 200 mJ in an open air. An echelle type spectrograph equipped with time controlled ICCD camera was used to resolve the emission spectrum from plasma. Ti I spectral lines at wavelengths of 453.32 and 498.17 nm were identified with recorded enhancement factors up to ×20, and this was achieved at the lower laser fluence of 4 J/cm 2. Strong reduction in the plasma ignition threshold by factor of 40 from the pure bulk titanium to nano-gold coated titanium was achieved, with similar reduction of limit of detection LOD. A theoretical work is in advance to explain the origin of the enhanced emission.
TrAC Trends in Analytical Chemistry
Abstract Common fertilizers have the oxidizing and the reducing elements on the same molecule; th... more Abstract Common fertilizers have the oxidizing and the reducing elements on the same molecule; therefore they have an explosiveness nature. Reliable approach for fast recognition of such compounds is an urgent need. Laser induced photoacoustic spectroscopy is an interesting technology as it can offer characteristic thermal, acoustical, and light absorption coefficient. The paper deals with a photoacoustic spectroscopy technique to record the characteristic photoacoustic frequency-response of common explosive-related materials. The proper stimulating light was generated using pulsed Q-switched Nd:YAG laser at 1064 nm. Photoacoustic signature for each investigated material was recorded using high response piezoelectric transducer. The captured signal was processed using novel digital algorithm designed for time and frequency domain analysis to achieve good discrimination between different explosive-related materials. Each investigated material demonstrated a characteristic absorption coefficient as well as frequency response with maximum amplitude at 47.9, 49, and 46 MHz for urea nitrate, ammonium nitrate, and ammonium perchlorate respectively.
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Papers by Ashraf El-Sherif