Laser Discharge Research Articles

Numerical simulation of laser energy discharge for flight control

The numerical investigation of the interaction of an off-axis laser discharge in front of an ogive cylinder at Mach 3.4 is presented. Details of the physics of the interaction of the blast wave and heated region with the ogive cylinder shock structure and the effect of this interaction on the drag, side force and pitching moment are included. The location of laser discharge and the amount of energy added to the gas by the laser are two main factors affecting the flow. Increasing the energy absorbed by the gas increases the drag reduction, the desired side force and pitching moment. Increasing the distance of the discharge from the axis reduces both drag reduction and side force achieved by the laser discharge.

Elemental analysis and mixture ratio determination in fine powder metals using microwave-sustained plasma ball spectroscopy

Elemental analysis of fine powder metals and their mixtures using plasma ball spectroscopy has been developed. This method is suitable for in situ and on-site industrial/ non-industrial monitoring applications; pre-treatment or powder fixation methods which are necessary for laser-induced breakdown spectroscopy were not required. The metals analysed were Cu, Mo and Pb with average grain size of ≤75 μm. A plasma seed (generated by laser or spark discharge) was spatially sustained in air at atmospheric conditions in a spherical form and controlled temporally using a semiconductor microwave (MW) oscillator; hence, the name plasma ball. The frequency and output power range of continuously oscillated MW were 2.45 GHz and 20–150 W respectively. Longer lifetime, controllability, non-thermal and stable plasma generation, as well as comparatively large volume of MW-sustained plasma made PBS of powder metals practically possible. Calibration curves were obtained for Cu-Mo and Cu-Pb mixtures, from which the concentration limit of detection (LOD) for both Mo and Pb powders were obtained as a function of the MW oscillation duration. The optimum concentration LOD for Mo and Pb powders in their constituent mixtures were respectively 0.004% and 0.002% by weight.

Using Low Temperature, Cost-effective and Green Methods to Carbon Nanohorn Synthesis

Background: Laser ablation method has high-yield and pure SWCNHs. On the other hand, arc discharge methods have low-cost production of SWCNHs. However, these techniques have more desirable features, they need special expertness to use high power laser or high current discharge that either of them produces very high temperature. As for the researches, the temperatures of these techniques are higher than 4727°C to vaporize the graphite. So, to become aware of the advantages of SWCNHs, it is necessary to find a new way to synthesize SWCNHs at a lower temperature. In other words, reaction field can be expandable at a moderate temperature. This paper reports a new way to synthesize SWCNHs at an extremely reduced temperature. Methods: According to this study, the role of N2 is the protection of the copper holder supporting the graphite rod by increasing heat transfer from the holder. After the current of 70 A was supplied to the system, the temperature of graphite rod was raised to 1600°C. It is obvious that this temperature is somehow higher than the melting point of palladium, 1555°C, and much lower than graphite melting point, 3497°C. Results: Based on the results, there are transitional precursors simultaneous with the SWCNHs. This composition can be created by distortion of the primary SWCNTs at the higher temperature. Subsequently, each SWCNTs have a tendency to be broken into individual horns. With increasing the concentration of the free horns, bud-like SWCNHs can be produced. Moreover, there are individual horns almost separated from the mass of single wall carbon nanohorns. This structure is not common in SWCNHs synthesized by the usual method such as arc discharge or laser ablation. Through these regular techniques, SWCNHs are synthesized as cumulative particles with diameters about 30-150 nm. Conclusion: A simple heating is needed for SWCNTs transformation to SWCNHs with the presence of palladium as catalyst. The well-thought-out mechanism for this transformation is that SWCNTs were initially changed to highly curled shape, and after that were formed into small independent horns. The other rout to synthesize SWCNHs is the pyrolysis of palm olein at 950°C with the assistance of zinc nitrate and ferrocene. Palm olein was used as a promising, bio-renewable and inexpensive carbon source for the production of carbon nanohorns.

Theoretical analysis of a hybrid TE-TEA CO2 laser

The output properties of a hybrid configuration containing a low pressure and an atmospheric pressure pulsed CO2 laser are theoretically analyzed. The simulation is performed based on the Six-Temperature Vibrational-Rotational Dynamic Model (6TVRM). The laser discharge tube is modeled by a non-linear distributed lumped electric circuit and the electron density is calculated by Transmission Line Method (TLM). The rotational transitions affecting the population of the upper and lower laser levels are also taken into account. The calculations were done by solving a set of differential equations using Runge-Kutta method in MATLAB software environment. It has been shown that using the above mentioned models leads to a significantly better agreement of the simulation results with the associated experimental data.

Tuning ignition and energy release properties of Zirconium powder by atomic layer deposited metal oxide coatings.

Ultra-fine powders of reactive metals are promising fuels/additives for propellants. However, the metal surfaces make these materials very unstable in ambient atmosphere. This study explored the method of applying thin films of inorganic materials onto the surface of Zr powder and investigated the effects of different surface coatings on the energy release and ignition process of Zr. Thin films of Al2O3 and ZnO were deposited on a commercial micron-scale Zr powder by atomic layer deposition (ALD). Growth kinetics of ALD films on the Zr particles were studied using various tools. Chemical and structural characterizations revealed that the Zr particles were completely encapsulated by uniform Al2O3 or ZnO films. The thicknesses of the encapsulation layers could be precisely controlled. ALD Al2O3 coatings exhibited a unique surface-sealing effect, which inhibited the low temperature oxidation of Zr in ambient air. Laser and electrostatic discharge (ESD) ignition tests revealed that ALD Al2O3 coatings extended the ignition delay and reduced the ESD sensitivity of the Zr powder. In comparison, ALD ZnO coatings could not form effective gas diffusion barriers, therefore they could not change the oxidation process of Zr and only showed modest effects on ignition and ESD sensitivity of the Zr powder.

Time-resolved spectroscopy of femtosecond laser-induced Cu plasma with spark discharge

The combination of spark discharge and laser-induced breakdown spectroscopy (LIBS) is called spark discharge assisted LIBS. It works under laser-plasma triggered spark discharge mode, and shows its ability to enhance spectral emission intensity. This work uses a femtosecond laser as the light source, since femtosecond laser has many advantages in laser-induced plasma compared with nanosecond laser, meanwhile, the study on femtosecond LIBS with spark discharge is rare. Time-resolved spectroscopy of spark discharge assisted femtosecond LIBS was investigated under different discharge voltages and laser energies. The results showed that the spectral intensity was significantly enhanced by using spark discharge compared with LIBS alone. And, the spectral emission intensity using spark discharge assisted LIBS increased with the increase in the laser energy. In addition, at low laser energy, there was an obvious delay on the discharge time compared with high laser energy, and the discharge time with positive voltage was different from that with negative voltage.

Condensation of water vapor underneath an inclined hydrophobic textured surface machined by laser and electric discharge

Condensation of water vapor on a surface plays an important role in thermal based water purification methods. Appropriate texturing of such surfaces facilitates dropwise condensation with better heat transfer coefficient and water collection. In this context, we explore texturing patterns via laser ablation to achieve lower aspect ratio (10 μm depth to 100 μm width) and via wire electric discharge machining process for higher aspect ratio (300 μm depth to 100 μm width). The transition from Cassie-Baxter to Wenzel is seen experimentally as well as through the simulations for lower aspect ratio, whereas the transition does not occur for higher aspect ratio. Simulations are also carried out for the sessile as well as pendant drop, which is more relevant to thermal based water purification. However, in the experiments the drop is always in the pendant mode. The condensing surface inclination plays a very significant role in the water collection. In order to have more water production underneath the copper plate, the optimum angle of inclination found is 35°.

MP17-05 THE IMPACT OF LASER PULSE LENGTH AND TYPE ON “POPCORN” LITHOTRIPSY

INTRODUCTION AND OBJECTIVES:Non-contact or “popcorn” lithotripsy is characterized by continuous laser discharge within a collection of stone fragments resulting in agitation of the stones and surro...

WELDING OF NITINOL BY SELECTED TECHNOLOGIES

Nitinol is a perspective alloy that is difficult to weld because of its high sensitivity to heat, atmospheric gases and the NiTi phase instability. We evaluated several welding techniques with regard to their applicability to weld fine pseudoelastic NiTi wires. Namely, we tested the microplasma arc, laser, electron beam, resistance and capacitor discharge welding. In conclusion, the behaviour of the weld for any of the implemented welding techniques is similar; it leads to a loss of mechanical properties in the welded joint caused by a recrystallization and an increased amount of brittle intermetallic phases. Yet, under perfect shielding and with a minimum heat input, the welds could, as a whole, retain the majority of their properties, and, as such, have the desired properties close to the base metal.

Jet and Shock Wave from Collapse of Two Cavitation Bubbles

As a common hydrodynamic phenomenon, multi-cavitation dynamics is widely found in many industries such as hydraulic engineering, shipping industry and chemical industry. The jet and shock wave phenomenon in the interaction of two cavitation bubbles are the basis of multi-cavitation bubbles interaction research. By respectively inducing two cavitation bubbles through laser and underwater low-voltage discharge, this paper tested the jet and shock wave resulting from the collapse of the two cavitation bubbles, and the following conclusions are obtained: (1) If the two cavitation bubbles are synchronously generated but in different size, as the distance between the two cavitation bubbles increases or the maximum radius of the smaller cavitation bubble increases, the effect of the small cavitation bubble on the larger one gradually changes from the surface wave phenomenon to jet that breaks through the larger bubble. When the two bubble center lines are parallel to the wall surface, this jet suppresses the formation of the jet to the wall surface when the large cavitation bubble collapses; if the two cavitation bubbles are generated at the same time with same size, as the initial distance of the two cavitation bubbles gradually decreases, the two bubbles are more likely to form a face-to-face collapse, and the smaller the distance between the two, the easier it is to fuse. (2) The impact of the initial moment of the cavitation bubble on the structure of the collapse shock wave is as follows: for two bubbles of different sizes formed synchronously, the shock wave propagates to the periphery in the form of a number of consecutive waves appearing in the larger bubble, while for the unsynchronized ones, shock waves appeared in both cavitation collapses, and a number of consecutive waves appear in the late-formed cavitation bubble. And multiple consecutive shock waves may overlap in some areas of the space. These conclusions have obvious implications for preventing cavitation damage and utilization of cavitation.

Progress of Sonic-Spray Ionization Mass Spectrometry and Its Applications

Abstract Sonic-spray ionization (SSI) is a previously developed soft ionization technique which does not need auxiliary methods such as voltage, heating, laser, or corona discharge. Spray ionization can be achieved under normal temperature and atmospheric pressure by inputting high-speed gas coaxial within the capillary. As an atmospheric pressure ion source, this technique was widely used as the interface of liquid chromatography-mass spectrometry at the beginning of its development. Based on the principles of sonic-spray ionization, a variety of easy ambient sonic-spray ionization derived techniques have been developed, which can be used for the in-situ, rapid and real-time analysis of samples with little or without any sample pretreatment. In this paper, the principless and characteristics of sonic-spray ionization were elaborated, and the progress of its application in life sciences, food safety, forensic chemistry, reaction monitoring, and other related fields were summarized.

Measurements of Iron Loss in PMSM Stator Cores Based on CoFe and SiFe Lamination Sheets and Stemmed From Different Manufacturing Processes

This paper deals with the experimental study of the iron losses under real operating conditions of a permanent magnet synchronous machine. The latter is a high frequency (>1 kHz) and high power-to-weight ratio (4 kW/kg) motor intended for an aerospace application. The measurements were carried out on different laminated stator cores based on classical commercial grades, namely, the NO20 and M270-35A for the silicon–iron alloy and the Vacodur49 (0.2 mm) for the cobalt–iron alloy. The lamination sheets stemmed from different manufacturing processes: insulation (bonding varnish and C5 varnish), cutting (laser and electrical discharge machining), and thermal treatment (fully processed only and fully processed + thermal re-treatment after cutting). We measured the iron losses at no load and over a wide range of frequency (speed) until around 1400 Hz, and then we compared them to the estimations yielded by the finite-element model under ANSYS Maxwell. Hence, this allowed us to accurately assess the iron loss add-on factor ( $K_{\mathrm {add}}$ ), which takes into account the extra magnetic loss caused by a complex magneto-thermo-mechanical coupling within the ferromagnetic material. This coupling occurs during the manufacturing and the assembly phase (cutting, welding, stacking, shrink fitting, …) and also during the real running conditions of an electrical machine (elliptic field, local saturation, high frequency, and harmonics).

Visualization of electro-physical and chemical machining processes

This paper aims to visualize spatio-temporal phenomena in electro physical and chemical processes in order to understand machining mechanisms and to achieve a technological breakthrough. In situ measurement methods to visualize the time evolution of stress, strain, temperatures, fluid velocities, and species density distributions, together with 2D or 3D images of the workpieces being processed are summarized. Applications of these methods to fundamental studies on electrical discharge machining, electrochemical machining, laser processing and additive manufacturing are introduced. Signal recording and processing technologies and real time monitoring enabling closed-loop feedback control are also discussed.

The continuous control of output power of a CuBr laser by a pulsed external magnetic field

Abstract An axial pulsed external magnetic field (EMF), instead of continuous one, has been applied on the operation of a CuBr laser with small-bore tube. A double synchronize triggering system has been designed and used for the laser pumping and simultaneously applying a magnetic field pulses up to 1100 Gauss. By applying an EMF along the tube axis, the laser output power has been decreased. Through adjusting the delay timing between triggers of magnetic field and laser discharge circuits, the laser output power can be changed, continuously. The maximum decrease of the laser output power has been obviously observed at a delay time of 120 ns between triggers.

Continuous synthesis of aligned carbon nanotube arrays on copper substrates using laser-activated gas jet

A method has been developed for continuous synthesis of carbon nanotube (CNT) arrays on large-area metal substrates using a reactor that moves above the substrate surface with a given scan rate. The reagent vapors pass through the region of plasma laser discharge towards the substrate surface screened by an argon flow from the external atmosphere. Vertically aligned multi-walled CNTs (MWCNTs) are formed on copper as a result of decomposition of ethylene and the vapor of iron pentacarbonyl. The main parameters of laser plasma discharge, gas jets, and concentrations of feed compounds have been estimated in terms of their effect on the growth rate and MWCNT morphology. The measurements of MWCNTs/Cu field emission characteristics have been used to determine optimal synthesis parameters for the fabrication of effective field emission cathodes.

Evaluation of surface integrity after high energy machining with EDM, laser beam machining and abrasive water jet machining of alloy 718

Development of future aero engine components based on new design strategies utilising topological optimisation and additive manufacturing has in the past years become a reality. This allows for designs that involve geometries of “free form” surfaces and material combinations that could be difficult to machine using conventional milling. Hence, alternative manufacturing routes using non-conventional high energy methods are interesting to explore. In this investigation, the three high energy machining methods abrasive water jet machining (AWJM), electrical discharge machining (EDM) and laser beam machining (LBM) have been compared in terms of surface integrity to the reference, a ball nosed end milled surface. The results showed great influence on the surface integrity from the different machining methods. It was concluded that AWJM resulted in the highest quality regarding surface integrity properties with compressive residual stresses in the surface region and a low surface roughness with texture from the abrasive erosion. Further, it was shown that EDM resulted in shallow tensile residual stresses in the surface and an isotropic surface texture with higher surface roughness. However, even though both methods could be considered as possible alternatives to conventional milling they require post processing. The reason is that the surfaces need to be cleaned from either abrasive medium from AWJM or recast layer from EDM. It was further concluded that LBM should not be considered as an alternative in this case due to the deep detrimental impact from the machining process.

Residual-stress-induced helical long period fiber gratings for sensing applications.

We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO2 laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.

Researches regarding injection moulding of polymeric products in moulds with micro-profiled surfaces

Injection moulding is one of the most commonly used manufacturing processes for composite polymeric products, with high challenges. Dimensional accuracy, optimal mechanical-physical properties as well as very good aesthetic of the polymeric products are requiring a precise controlled injection moulding system. The mould precision influences the product’s tolerances and the good functioning of the injection moulding system. The mould surfaces are important for aesthetic but also for filling, packing and de-moulding of the product. In this paper we present an analyse of 4 different technologies for manufacturing the micro-profiled mould surfaces of a folk motive pattern from Neamţ County Romania and few geometric figures on the direction and perpendicular on the direction of the flow, with details of 100, 250 and 500 μm with height from 10 to 100 μm: high speed milling, electrical discharge machining, laser engraving and chemical etching. The goal is to find out the applicability domain for each technology, economic and precision criteria. The experiments consisting in building the micro-profiled surfaces mould and in injection moulding a recycled re-granulated polystyrene basis polymer evidenced the cost / precision ratio for each technology and which one is better economically suited depending on the requirement.

Methodic of the computer calculation of the plasma impedance of the glow discharge lasers

In this work an expression for the dynamic resistance of a glow discharge in long tubes was obtained and analyzed. The expression describes the physical processes taking place in the positive column of a glow discharge. The analysis of the frequency dependences of the active and reactive constituents, as well as the dynamic resistance module for discharge conditions corresponding to glow discharge lasers, was performed. On the basis of the expressions obtained a computer program for modeling the dynamic resistance of discharge was developed. The program allows you to calculate and display the plots of the frequency dependences of the active and reactive constituents, as well as the module of the dynamic resistance of the discharge gaps of lasers. Also, the program provides a function for constructing hodographs of dynamic resistance.

Phase difference meter between the alternating current and voltage components for determining the impedance of plasma of glow discharge lasers

In this work meter for the phase difference of the variable components of the discharge current and the voltage drop was developed and tested. The operation of the meter is based on the transformation of harmonic signals into rectangular pulses, and further determination of the time shift between them. The possibility of using this meter for monitoring the dynamic resistance of glow discharge lasers is shown.