932 results
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2. X-ray microtomography and laser ablation in the analysis of ink distribution in coated paper.
- Author
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Myllys, M., Häkkänen, H., Korppi-Tommola, J., Backfolk, K., Sirviö, P., and Timonen, J.
- Subjects
LASER ablation ,X-ray computed microtomography ,INK chemistry ,PERMEABILITY of paper coatings ,PROFILOMETER ,PENETRATION mechanics - Abstract
A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 μm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
3. Filter paper loaded with gold nanoparticles as flexible SERS substrates for sensing applications.
- Author
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Bharathi, Moram Sree Sathya, Byram, Chandu, Nehra, Kamalesh, Kumar, P. Senthil, Rao, Soma Venugopal, Sharma, Veerendra K., Prajapat, C. L., and Yusuf, S. M.
- Subjects
- *
FILTER paper , *RAMAN scattering , *FEMTOSECOND lasers , *LASER ablation , *NEAR-fields , *GOLD nanoparticles - Abstract
Surface-Enhanced Raman Scattering (SERS) performance of filter paper (FP) loaded with gold nanoparticles (Au NPs) of three different size/shapes (spherical, triangular and star) were investigated. Spherical Au NPs were synthesized using femtosecond laser ablation of Au target in distilled water and other two anisotropic (triangular and star-shaped) Au NPs were prepared by colloidal chemical methods. COMSOL Multiphysics simulations were performed to investigate near field distributions of these Au NPs and as expected, the strongly enhanced near-field intensity at the sharp features was observed. The SERS performance [using the dye molecule Nile Blue (NB)] of star-shaped Au NPs loaded FP was superior compared to the triangle and spherical Au NPs loaded FP due to the presence of sharp tips and thus it was proved to be capable of detecting 10 pM NB concentration with an estimated enhancement factor of ∼3.7×1010. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
4. A Sensor for Laser Ultrasonic Measurement of Elastic Properties of Moving Paper.
- Author
-
Ridgway, P., Russo, R., Lafond, E., Jackson, T., and Zhang, X.
- Subjects
INDUSTRIAL lasers ,MIRRORS ,MEDICAL imaging systems ,LASER ablation ,ULTRASONIC equipment ,INDUSTRIAL applications of ultrasonic waves - Abstract
An automated, non-contact, non-destructive sensor has been developed for measurement of sheet flexural and shear rigidity in paper manufacturing. It was tested on a pilot web handler at web speeds up to 25.4 m/s. A model equation was fitted to the frequency dependence of the phase velocity of Ao mode Lamb waves. Ultrasound was generated in paper with a pulsed Nd:YAG laser and detected with a Mach-Zehnder interferometer coupled with a scanning mirror/timing system to compensate for paper motion. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
5. X-ray microtomography and laser ablation in the analysis of ink distribution in coated paper
- Author
-
Myllys, Markko, Häkkänen, Heikki, Korppi-Tommola, Jouko, Backfolk, K., Sirviö, P., and Timonen, Jussi
- Subjects
tomografia ,kuva-analyysi ,topografia ,Surface structure ,Laser ablation - Abstract
A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 lm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate. peerReviewed
- Published
- 2015
6. Rear side optimization for mass production PERC solar cell with efficiency above 23%.
- Author
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Zhang, Shude, Zhao, Baoxing, Lian, Weifei, Kuang, Yawei, Liu, Yushen, and Ni, Zhichun
- Subjects
SOLAR cell efficiency ,MASS production ,SILICON solar cells ,SOLAR cells ,REFRACTIVE index ,LASER ablation ,PHOTOVOLTAIC power systems - Abstract
When LDSE (Laser Doped Selective Emitter) is applied to the front side of PERC solar cell, the low sheet resistance requirement for metal contact can be realized by laser doping. Therefore, at present the front sheet resistance has increased from 85 Ω to 140±10 Ω. The emitter saturation current density reduces from 100 fA/cm
2 to less than 50 fA/cm2 . Therefore, the rear surface optimization of PERC solar cell becomes more and more important. In this paper, three aspects about the rear surface are studied. Firstly, the effects of alkali polishing and acid polishing on the performance of LDSE PERC solar cell are compared for the improvement of rear surface polishing. Then, bilayer SiNx :H capping film is adoped on the Al2 O3 layer instead of monolayer SiNx :H. The bottom layer of bilayer structure is made up of high refractive index SiNx :H, which can improve the hydrogen passivation effect. The top layer of bilayer structure is made up of low refractive index SiNx :H, which can improve the resistance to aluminum paste erosion. Finally, the influence of different kinds of laser ablation patterns on the cell performance is investigated, aiming to optimize the metal contact recombination. Benefiting from the three methods above, an average efficiency of 23.1% and a champion efficiency of 23.3% are achieved. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
7. Long-range oscillations of a laser-produced carbon plasma recorded by an electrostatic energy analyzer.
- Author
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Nica, Petru-Edward, Ursu, Cristian, and Focsa, Cristian
- Subjects
LASER plasmas ,ELECTROSTATIC analyzers ,LASER ablation ,CHARGE carriers ,OSCILLATIONS ,RUTHERFORD backscattering spectrometry - Abstract
Understanding peculiar dynamics in transient laser-produced plasmas is of great importance for a number of applications such as energetic ion production, ion implantation, laser micro-machining, etc. Continuing a series of papers on the electrical and optical characterization of laser ablation plasma plumes, we report here on the observation of oscillations in the ionic and electronic currents at a long distance (17.5 cm) from the ablation target. An electrostatic energy analyzer was used to finely probe the dynamics of charge carriers in a carbon plasma generated in vacuum by KrF excimer laser ablation of a graphite target. A short-time Fourier transform data processing approach was applied to extract valuable information from the recorded currents. This method not only reveals different frequencies for two distinct expanding plasma structures, but also unveils different trends in their temporal evolution. These new experimental results corroborate previous studies supporting a scenario based on the plasma structuring in multiple double layers. A discussion with respect to an alternative scenario based on low-frequency sheath instabilities is also presented. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
8. Effect of a textured surface on the occurrence and development of cavitation on the hydrofoil.
- Author
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Skripkin, Sergey G., Starinskiy, Sergey V., Tsoy, Mikhail A., Vasiliev, Mikhail M., and Kravtsova, Aleksandra Yu.
- Subjects
CAVITATION ,HYDROFOILS ,SURFACE morphology ,LASER ablation - Abstract
An experimental study of the cavitation flow around the National Advisory Committee for Aeronautics 0012 hydrofoil with different surface morphology was carried out in this work. The surface morphology was set by modern laser ablation technology. The average values and intensity of vapor–gas cavities were determined. It has been revealed that laser texturing delays the emerging cavitation and somewhat decreases its intensity at higher cavitation numbers. A decrease in the cavitation number leads to an increase in its intensity for a smooth hydrofoil in comparison with a rough one, which is also expressed in an increase in the frequency of cavities. The paper presents a comparison of the flow regime with equal cavitation numbers, which clearly describes the features of the development of a vapor–gas cavity on the suction side of the foil with different surface morphologies. The paper provides an explanation of the reasons for the influence of surface morphology on the development of cavities. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
9. Beamed Energy Propulsion by Means of Target Ablation.
- Author
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Rosenberg, Benjamin A.
- Subjects
LASER ablation ,AERONAUTICS ,INDUSTRIAL lasers ,LASERS ,ENERGY development ,POWER resources ,RESEARCH - Abstract
This paper describes hundreds of pendulum tests examining the beamed energy conversion efficiency of different metal targets coated with multiple liquid enhancers. Preliminary testing used a local laser with photographic paper targets, with no liquid, water, canola oil, or methanol additives. Laboratory experimentation was completed at Wright-Patterson AFB using a high-powered laser, and ballistic pendulums of aluminum, titanium, or copper. Dry targets, and those coated with water, methanol and oil were repeatedly tested in laboratory conditions. Results were recorded on several high-speed digital video cameras, and the conversion efficiency was calculated. Paper airplanes successfully launched using BEP were likewise recorded. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
10. Effect of the surface pattern on the drag property of the superhydrophobic surface.
- Author
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Chen, Qiaodan, Duan, Jun, Hou, Zhongbao, Hou, Guoxiang, and Deng, Leimin
- Subjects
SUPERHYDROPHOBIC surfaces ,DRAG reduction ,SURFACE properties ,LASER ablation ,WETTING ,SPEED - Abstract
Superhydrophobic surfaces with a slip effect have been proven to be effective to achieve surface drag reduction. In this paper, we fabricated superhydrophobic disks via laser ablation and chemical modification, and their drag-reduction performance is tested by a rheometer. However, the superhydrophobic disk achieves a limited drag-reduction effect (33.5% in maximum) with poor consistency (decay rapidly as rotating speed increases). To enhance the drag-reduction performance of the superhydrophobic surfaces, surfaces with tunable patterns consisting of superhydrophobic and hydrophobic surfaces are proposed. The difference in wettability and slip length between different regions is employed to control the flow direction. The effect of different patterns is investigated both experimentally and numerically, and the results indicate that the pattern distribution performs a great impact on the drag-reduction effect. The pattern consistent with the primary flow can not only enhance the effect (60.3% in maximum) but also the consistency (maintained at a higher rotating speed) of drag-reduction. On the contrary, the pattern perpendicular to the flow direction is harmful to drag reduction and can even increase the drag. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
11. Effect of magnetic field-dependent effective thermal conductivity of melted layer on nanosecond laser ablation of copper and formation of nanoparticles at atmospheric air pressure.
- Author
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Singh, Khwairakpam Shantakumar and Sharma, Ashwini Kumar
- Subjects
LASER ablation ,AIR pressure ,ATMOSPHERIC pressure ,THERMAL conductivity ,LIQUID metals ,COPPER - Abstract
For a nanosecond laser ablation of metals, the key physical phenomena involved are thermal evaporation, melt ejection, instability of the molten metal, etc., which depend on the initial temperature evolution in the metal. Understanding the evolution of temperature of the metal needs an effective simulation. In the present paper, we report on the finite element method-based simulation of nanosecond laser ablation of copper in the absence and presence of the magnetic field. Our studies showed that the effective thermal conductivity of the melted layer on the copper surface in the presence of the magnetic field affects the viscosity of the layer, mass ablation rate, instability, and then particle formation. The calculations showed that the condensed nuclei of large critical size are produced in the magnetic field. It is attributed to an increase in the collision rate of plasma particles in the magnetically confined plasma. The simulations are in good agreement with the experimentally measured values. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
12. Beamed Energy Propulsion: Research Status And Needs—Part 2.
- Author
-
Birkan, Mitat
- Subjects
CONFERENCES & conventions ,SPACE flight propulsion systems ,INDUSTRIAL lasers ,ELECTROMAGNETIC waves ,POWER resources ,LASER ablation - Abstract
One promising solution to the operationally responsive space is the application of remote electromagnetic energy to propel a launch vehicle into orbit. With beamed energy propulsion, one can leave the power source stationary on the ground or space, and direct heat propellant on the spacecraft with a beam from a fixed station. This permits the spacecraft to leave its power source at home, saving significant amounts of mass, greatly improving performance. This concept, which removes the mass penalty of carrying the propulsion energy source on board the vehicle, was first proposed by Arthur Kantrowitz in 1972; he invoked an extremely powerful ground based laser. The same year Michael Minovich suggested a conceptually similar “in-space” laser rocket system utilizing a remote laser power station. In the late 1980's, Air Force Office of Scientific Research (AFOSR) funded continuous, double pulse laser and microwave propulsion while Strategic Defense Initiative Office (SDIO) funded ablative laser rocket propulsion. Currently AFOSR has been funding the concept initiated by Leik Myrabo, repetitively pulsed laser propulsion, which has been universally perceived, arguably, to be the closest for mid-term applications. This 2-part paper examines the investment strategies in beamed energy propulsion and technical challenges to be covers Part 2 covers the present research status and needs. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
13. Laser Propulsion with Liquid Propellants Part I: an Overview.
- Author
-
Sinko, John E. and Pakhomov, Andrew V.
- Subjects
CONFERENCES & conventions ,LASER ablation ,INDUSTRIAL lasers ,LIQUID propellants ,ROCKET fuel ,PROPELLANTS - Abstract
Despite years of research, laser propulsion on liquid propellants has yet to achieve specific impulses greater than tens of seconds. It is well established that liquids, when used as propellants, can provide coupling coefficient (C
m ) on the order of 100–1000 dyne/W. However, the specific impulse (Isp ) has proven to be significantly inferior to that for solid propellants. This paper will examine the various laser propulsion schemes based on ablation of liquid propellants and intended primarily for space applications. The principal shortcomings associated with liquid propellants will be outlined. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
14. Calibration and Validation of a 6-DOF Laser Propelled Lightcraft Flight Dynamics Model vs. Experimental Data.
- Author
-
Kenoyer, David A., Anderson, Kurt S., and Myrabo, Leik N.
- Subjects
CONFERENCES & conventions ,LIGHT amplifiers ,INDUSTRIAL lasers ,LASER beams ,LASER ablation - Abstract
A detailed description is provided of the flight dynamics model and development, as well as the procedures used and results obtained in the verification, validation, and calibration of a further refined, flight dynamics system model for a laser lightcraft. The full system model is composed of individual aerodynamic, engine, laser beam, variable vehicle inertial, and 6 DOF dynamics models which have been integrated to represent all major phenomena in a consistent framework. The resulting system level model and associated code was then validated and calibrated using experimental flight information from a 16 flight trajectory data base. This model and code are being developed for the purpose of providing a physics-based predictive tool, which may be used to evaluate the performance of proposed future lightcraft vehicle concepts, engine systems, beam shapes, and active control strategies, thereby aiding in the development of the next generation of laser propelled lightcraft. This paper describes the methods used for isolating the effects of individual component models (e.g. beam, engine, dynamics, etc.) so that the performance of each of these key components could be assessed and adjusted as necessary. As the individual component models were validated, a protocol was developed which permitted the investigators to focus on individual aspects of the system and thereby identify phenomena which explain system behavior, and account for observed deviations between portions of the simulation predictions from experimental flights. These protocols are provided herein, along with physics-based explanations for deviations observed. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
15. Delrin® for Propulsion with CO2 Laser: Carbon Doping Effects.
- Author
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Sinko, John E., Pakhomov, Andrew V., Millen, Stewart, Zhu, Jane, Sinko, Robert J., and Potts, Kenneth
- Subjects
CONFERENCES & conventions ,LASER ablation ,INDUSTRIAL lasers ,SPECTRUM analysis ,LIGHT amplifiers - Abstract
Polyoxymethylene (POM) a.k.a. Delrin has been commonly used for propulsion with carbon dioxide (CO
2 ) lasers as a solid fuel providing excellent combination of coupling coefficient and specific impulse. In this paper the propulsive characteristics of white and black (carbon-doped) Delrin will be examined and compared. A Transverse Electric discharge in gas at Atmospheric pressure (TEA) CO2 laser with 300 ns pulse width was operated at up to 20 J pulse energy to produce irradiances on the order of 1–500 MW/cm2 on Delrin targets. Fourier Transform Infrared (FTIR) spectroscopy, time-resolved force sensors, a ballistic pendulum, and Schlieren imaging techniques were used to determine absorption spectra, coupling coefficient, specific impulse, and internal efficiency of Delrin. An analysis will be made of the possible routes for force generation. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
16. Near-Term Application of Water-Powered Laser-Propulsion.
- Author
-
Baasandash, Choijil, Yabe, Takashi, Oku, Takehiro, Ohkubo, Tomomasa, Yamaguchi, Masashi, Ohzono, Hirokazu, Taniguchi, Kazumoto, Miyazaki, Sho, Akoh, Ryosuke, Ogata, Yoichi, and Fushinobu, Kazuyoshi
- Subjects
WATER supply ,LASER ablation ,SPACE vehicles ,LASERS ,PROPULSION systems ,ENGINEERING systems - Abstract
We found that water overlay on a metal layer is more effective than solid overlay. By using this target we demonstrated the successful flight of paper-airplane of 5 cm-size over a distance of 1–2m. In this paper, repetitive water supply system and levitation system are proposed for practical application, and examined by experiments. We succeeded in driving an object continuously using repetitive water supply and air slider. We also succeeded in driving 300g object by 0.5J laser using these equipments. In this paper, we try to find out a new possibility of water-powered laser propulsion. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
17. Ejecta distribution and transport property of fused silica under the laser shock loading.
- Author
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Shen, Rong-qi, Bai, Qing-shun, Li, Yu-hai, Guo, Yong-bo, and Zhang, Fei-hu
- Subjects
FUSED silica ,LASER peening ,GRANULAR flow ,FREE surfaces ,LASER ablation ,NANOPARTICLES - Abstract
Laser-induced particle ejection on the exit surface of fused silica serves as an important contaminant source in a high-power laser system. The transport process of molten silica particles in a gas environment or vacuum is important in understanding the change in size and temperature of silica particles, which influence the ultra-clean manufacturing of optical components. In this paper, the ejection process of fused silica is investigated using molecular dynamics simulation. The results show that the geometry of a surface scratch influences the mass of the microjet. With shallower groove depth and a smaller vortex angle, the mass of the microjet is less under shock loading. The size of ejected particles tends to decrease gradually and does not change any more eventually. Besides, these particles become dispersed during the transport process in a vacuum. On the other hand, background gas suppresses the particle flow and slows down the particle flow. As the ejected particles compress gas, vapor and small clusters (N < 50) are stripped from the microjet continuously. Eventually, the number of nanoparticles that exceed the free surface decreases to zero. The stripped small clusters behind the head of the microjet recombine with other clusters, which change the volume density of ejected particles near the free surface. The higher velocity of ejected particles induces a stronger gas stripping effect, which makes an increase in the number of small clusters (N < 50). The results can help understand the behavior of particle ejection and the transport process of silica particles in a gas environment or vacuum, especially in the field of laser-induced particle ejection on the exit surface or the laser ablation of fused silica producing aerosol. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
18. New thermal solver for mitigating surface temperature instability in laser-induced heating.
- Author
-
Zhu, Xun, Iyer, Kaushik A., and Luke, Darren
- Subjects
SURFACE temperature ,PHASE transitions ,LASER ablation ,TRANSPORT equation ,HEAT conduction - Abstract
An accepted approach to computing laser-induced peak surface temperature is to employ the enthalpy formulation of the transient heat conduction equation [Grigoropoulos et al., Adv. Heat Transfer 28, 75–144 (1996); Sawyer et al., J. Laser Appl. 29, 022212 (2017)]. This approach is generally implemented using an explicit numerical scheme to solve the thermal transport equation. While it offers the advantage of modeling the solid-melt phase transition automatically, the approach results in instability-like behavior in the computed surface temperature. When laser-induced ablation becomes significant, the heating rate in the surface cell becomes unrealistically large. This results in spikes in the computed peak surface temperature due to large errors in calculating the heating rate. In this paper, we present a new approach, which we refer to as the Moving Frame Solver, that employs a moving-coordinate frame of reference, located at the receding evaporating surface. We also use an analytical representation for the phase transition region of the enthalpy-temperature relationship. The Moving Frame Solver combined with an implicit scheme leads to a stable solution without surface temperature, pressure, or velocity spikes. In other words, any instability in these computed parameters due to use of an explicit scheme (such as Dufort–Frankel) has been eliminated. Details of the new thermal solver and example calculations are presented. Numerical experiments suggest that the surface cell size needs to be small, ∼0.1 μm, to obtain a highly accurate solution with a typical metal such as aluminum. Using the Moving Frame Solver with a refined grid near the surface, but coarse elsewhere, enables accurate and stable surface temperature computation. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
19. Influence of the material properties and the process parameters on the ablation behavior for the laser structuring of the diffusion media for fuel cells.
- Author
-
Geiger, Christian, Grabmann, Sophie, Weiss, Tony, Gruendl, Alena, and Zaeh, Michael F.
- Subjects
FUEL cells ,PROTON exchange membrane fuel cells ,GREENHOUSE gas mitigation ,LASER ablation ,ULTRA-short pulsed lasers ,MANUFACTURING processes ,INFRARED radiation ,SCANNING electron microscopes - Abstract
Hydrogen-powered polymer electrolyte membrane fuel cells (PEMFCs) show promising potential to power a wide range of mobile and stationary applications and to reduce greenhouse gas emissions significantly. In PEMFCs, the oxygen transport and the water transport are essential for a long lifetime and high-performance characteristics. The diffusion media (DM), located between the bipolar plate and the catalyst-coated membrane, is a crucial component of the fuel cell that significantly affects the cell-internal processes. Usually, the DM is a two-layer material system consisting of a microporous layer based on carbon black particles coated onto a porous gas diffusion layer (e.g., carbon paper). The properties of the microporous layer regarding the water transport at high current densities and, consequently, the fuel cell's performance and lifetime can be improved by laser structuring. Within this work, different microporous layers with varying binder content and porosities were structured by locally ablating the material using ultrashort-pulsed laser radiation in the infrared wavelength range. The effect of varying process parameters was additionally investigated. Furthermore, the ablation efficiencies were calculated for increasing pulse repetition rates to qualify a process window for an industrial structuring process. The size of the micro-drillings and the heat-affected zone surrounding the hole were evaluated through topographic and microstructure analyses using a laser scanning microscope and a scanning electron microscope with energy-dispersive x-ray spectroscopy. The results showed a rather small influence of the porosity and composition of the microporous layer on the ablation behavior. In contrast, the laser structuring parameters influenced the micro-drilling geometry significantly. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
20. Dynamic of shock–bubble interactions and nonlinear evolution of ablative hydrodynamic instabilities initialed by capsule interior isolated defects.
- Author
-
Liu, Y. X., Chen, Z., Wang, L. F., Li, Z. Y., Wu, J. F., Ye, W. H., and Li, Y. J.
- Subjects
LASER ablation ,SHOCK waves ,VORTEX motion ,COMPRESSIBILITY ,COLLISIONLESS plasmas ,MICROMETERS - Abstract
It is believed that isolated defects within the capsule (e.g., void, high-density inclusion) can be one of the essential factors for implosion performance degradation by seeding hydrodynamic instabilities in implosions. Nonetheless, a systematic study on how the isolated defects evolve and why they are not stabilized by ablation given the length scale comparable with the typical cutoff wavelength is still lacking. This paper addresses the above concerns by looking into a simplified model where a planar shell (without convergent geometry) is driven by laser direct-drive, with a single defect (low/high density) of micrometer or sub-micrometer scale residing at different locations inside. The underlying dynamics of two key physical processes are analyzed, i.e., the shock–bubble interactions as well as the subsequent nonlinear evolution of ablative hydrodynamic instabilities initiated by the direct interaction of the deformed defect and ablation front, revealing that compressibility and baroclinic effects drive vorticity production during the interactions between the shock wave and the isolated defect. In the "light-bubble" case, the vortex pair generated in the first process is further strengthened by the laser ablation. Hence, a directed flow is formed in companion with the persistent flow entering the bubble of the surrounding ablator. The bubble exhibits a remarkable growth both laterally and deeply, seriously threatening the shell's integrity. The positive feedback mechanism of the vortex pair is absent in the "heavy-bubble" counterpart, and the ablation stabilization manifested itself in the reduction of spike amplitude. A systematic study of localized perturbation growth as a function of defect placement, size, and preheating intensity is presented. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
21. Efficient numerical method for model kinetic equations as applied to pulsed laser ablation into vacuum.
- Author
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Titarev, V. A. and Morozov, A. A.
- Subjects
- *
LASER ablation , *DISTRIBUTION (Probability theory) , *PULSED lasers , *EQUATIONS , *VELOCITY - Abstract
The paper is devoted to the construction of the efficient numerical methods to solve model kinetic equations as applied to the pulsed laser ablation (evaporation) into vacuum. We briefly describe the general ALE-type discrete velocity method and outline the modifications required for the present study. Then, we compute a particular moderate-intensity flow using Nesvetay code and compare the results for time-of-flight distributions and average axial energies with those of the DSMC code LasInEx. An accurate calculation of these quantities involves integration of the velocity distribution function in very narrow conical parts of the molecular velocity space and therefore requires the usage of a specially constructed mixed-element unstructured velocity mesh. Good agreement confirms the robustness and accuracy of the proposed discrete velocity approach. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
22. Interaction of femtosecond laser radiation with a liquid medium at different pressures.
- Author
-
Chkalov, Ruslan and Kharkova, Alena
- Subjects
LASER beams ,LASER ablation ,LIQUID hydrocarbons ,LIQUIDS ,FEMTOSECOND lasers ,NANOSTRUCTURED materials - Abstract
This paper describes an experiment on the interaction of femtosecond laser radiation with a liquid hydrocarbon. The external pressure was changing using argon buffer gas. Hexane was using as a hydrocarbon. The processes were recording on two cameras at different scales. As a result of the experiment, the behavior of the liquid medium changed depending on the external pressure. During the experiment, it was founding that with an increase in the pressure value, the boiling intensity of the liquid decreases. The influence of the behavior of the liquid medium on the laser ablation process is investigating. These results can be using in the field of synthesis of nanomaterials [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
23. Laser Propulsion Standardization Issues.
- Author
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Scharring, Stefan, Eckel, Hans-Albert, Röser, Hans-Peter, Sinko, John E., and Sasoh, Akihiro
- Subjects
PROPULSION systems ,LASER ablation ,STANDARDIZATION ,LASER beams ,NONLINEAR optics ,LASERS ,COMPARATIVE studies - Abstract
It is a relevant issue in the research on laser propulsion that experimental results are treated seriously and that meaningful scientific comparison is possible between groups using different equipment and measurement techniques. However, critical aspects of experimental measurements are sparsely addressed in the literature. In addition, few studies so far have the benefit of independent confirmation by other laser propulsion groups. In this paper, we recommend several approaches towards standardization of published laser propulsion experiments. Such standards are particularly important for the measurement of laser ablation pulse energy, laser spot area, imparted impulse or thrust, and mass removal during ablation. Related examples are presented from experiences of an actual scientific cooperation between NU and DLR. On the basis of a given standardization, researchers may better understand and contribute their findings more clearly in the future, and compare those findings confidently with those already published in the laser propulsion literature. Relevant ISO standards are analyzed, and revised formats are recommended for application to laser propulsion studies. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
24. Thrust Measurements in Ballistic Pendulum Ablative Laser Propulsion Experiments.
- Author
-
Brazolin, H., Rodrigues, N. A. S., and Minucci, M. A. S.
- Subjects
CONFERENCES & conventions ,INDUSTRIAL lasers ,LASER ablation ,AERONAUTICS ,SPACE flight propulsion systems - Abstract
This paper describes a setup for thrust measurement in ablative laser propulsion experiments, based on a simple ballistic pendulum associated to an imaging system, which is being assembled at IEAv. A light aluminium pendulum holding samples is placed inside a 100 liters vacuum chamber with two optical windows: the first (in ZnSe) for the laser beam and the second (in fused quartz) for the pendulum visualization. A TEA-CO
2 laser beam is focused to the samples providing ablation and transferring linear moment to the pendulum as a whole. A CCD video camera captures the oscillatory movement of the pendulum and the its trajectory is obtained by image processing. By fitting the trajectory of the pendulum to a dumped sinusoidal curve is possible to obtain the amplitude of the movement which is directly related to the momentum transfered to the sample. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
25. Access to Space without Energy and Propellant on Board.
- Author
-
Sasoh, Akihiro, Jeung, In-Seuck, and Choi, Jeong-Yeol
- Subjects
LASER ablation ,PROPULSION systems ,ROCKETS (Aeronautics) ,PROPELLANTS ,SPACE flight propulsion systems ,AERIAL projectiles - Abstract
Laser-driven, in-tube accelerator is a laser propulsion device in which the impulse performance is enhanced by the confinement of the compressible fluid. This paper describes the conceptual origin and state of the art of this technology. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
26. Determination of copper, magnesium, and manganese in aluminum alloys using laser-induced breakdown spectroscopy based on fiber laser ablation.
- Author
-
Lv, Chao, Zhang, Ning, Lin, Zhanjian, Ou, Tianxue, Li, Jiaming, Zhao, Nan, Yang, Xinyan, Ma, Qiongxiong, Guo, Liang, and Zhang, Qingmao
- Subjects
LASER-induced breakdown spectroscopy ,ALUMINUM alloys ,FIBER lasers ,MANGANESE alloys ,COPPER ,LASER ablation - Abstract
Fiber lasers are characterized by high efficiency, good beam quality, and high reliability and are widely used in industries. In addition, the high repetition frequency of fiber lasers can increase the analytical efficiency greatly. In this paper, a nanosecond fiber laser was introduced to be the ablation source in laser-induced breakdown spectroscopy (LIBS) for determining copper, magnesium, and manganese in aluminum alloys. Because of the high repetition frequency of the fiber laser, the conventional delay-acquisition strategy was unavailable. Discrete wavelet transform (DWT) was used to mitigate the interference of the Bremsstrahlung background. Standard calibration and internal calibration methods were also compared for quantitative analyses. The results demonstrated that the combination of DWT and internal calibration effectively improved the analytical accuracy. After optimization, the R
2 s of the FL-LIBS system for Cu, Mg, and Mn were 0.9897, 0.9964, and 0.9979, respectively; the root mean squared error of cross validation was 0.0414, 0.0462, and 0.031 wt. %, respectively. This study provides a convenient method for the rapid elemental analysis of aluminum alloys. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
27. Texturing skin-pass rolls by high-speed laser melt injection, laser ablation, and electrolytic etching.
- Author
-
Warneke, Philipp, Bohlen, Annika, and Seefeld, Thomas
- Subjects
LASER ablation ,METALLIC composites ,ALUMINUM sheets ,ETCHING ,SURFACE texture - Abstract
Skin-pass rolls are used for setting the final sheet thickness and surface texture. For sheet metal that is produced for forming, textured skin-pass rolls featuring a high-low structure are used in order to improve the formability and paint adhesion of the sheet. In this paper, new textures for skin-pass rolls generated by high-speed laser melt injection (HSLMI) are presented and characterized. Furthermore, it is studied how the texture of the roll is transferred to steel and aluminum sheets. With HSLMI, metal matrix composite (MMC) layers featuring spherical fused tungsten carbide (SFTC) particles with a high hardness could be produced on skin-pass rolls. For generating an increased high-low structure, laser ablation and electrolytic etching were carried out after HSLMI and grinding of the rolls. An analysis of the topography showed that different protruding heights between SFTC particles and matrix can be set. The textures generated by laser ablation showed a topography featuring two homogeneous height levels, whereas a texture with spherically shaped particles could be generated by electrolytic etching. Furthermore, it was found that all textures were transferred from the roll to both steel and aluminum sheets. The transfer of the textures mainly depended on the protruding height of the SFTC particles and the SFTC particle content of the roll. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
28. A compact flexible sub-nanosecond framing photographic system.
- Author
-
Li, Xin-yan, Yuan, Peng, Wu, Li-xuan, Gao, Fan, and Zheng, Jian
- Subjects
- *
LASER-induced breakdown spectroscopy , *LASER ablation , *SHOCK waves , *THEORY of wave motion , *LASER plasmas - Abstract
A novel high-speed multi-frame photographic system is presented in this paper. The system demonstrates exceptional compactness and flexibility, requiring only the introduction of a cavity comprising multiple beam-splitters in the optical path to enable multi-frame imaging of sub-nanosecond events. The number and temporal delay of frames can be easily adjusted by adjusting the distance and angle between beam-splitters. These capabilities are demonstrated by observing the laser ablation process, highlighting the great potential for application in capturing ultrafast time-evolving events such as optical breakdown, the evolution of laser-produced plasmas, and the propagation of shock waves. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
29. Quasi-periodic micro-lens array via laser-assisted wet etching.
- Author
-
Baek, Gi Hyeon, Hwang, Eui Sun, and Cheong, Byoung-Ho
- Subjects
ETCHING ,FEMTOSECOND pulses ,LASER pulses ,LASER ablation ,MICROLENSES ,FEMTOSECOND lasers ,ULTRAVIOLET lasers - Abstract
A close-packed micro-lens array (MLA) is widely used not only in novel optical systems but also in various engineering fields, such as semiconductors and display devices. In this paper, we present a simple and efficient method for fabricating MLAs on a glass substrate via laser ablation with a single femtosecond laser pulse and chemical wet etching in a hydrofluoric acid solution. The shapes of concave micro-lenses were optimized for laser pulse energy and etching time, and ∼70 000 micro-lenses with 15 µm diameter were formed. The shape of the micro-lens varies significantly with respect to the etching time in accordance with an initial ablated area (or laser energy), which is a key feature in fabricating micro-lenses of several tens of μm. Using the glass MLA as a mold, a polydimethylsiloxane convex-plano lens array was replicated, and the performance of the optical imaging and beam integrator was then examined. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
30. Optimization of mesoporous silicon morphology adding by colloidal gold nano layer.
- Author
-
Hamood, Mahmood Ahmed, Ali, Ghazwan Ghazi, and Abed, Mazin Ahmed
- Subjects
- *
COLLOIDAL gold , *GOLD nanoparticles , *SCANNING electron microscopes , *LASER ablation , *SILICON wafers - Abstract
This paper provides some new insights into the gold nanoparticles on porous silicon formation and characterization. The porous silicon was prepared by Photo electrochemical etching method of n-type silicon wafer with orientation (100), resistivity (1.5-4 Ω.cm) and current density at 35 mA/cm2. This process involves using HF solution of 16% concentration at etching time 10 min and photo source of 100 m W/cm2. The laser ablation was carried out in this study in order to produce the gold nanoparticles using laser energy (300,400 and 500 m J). We have studied of surface properties of the prepared AuNPs/PSi samples by scanning electron microscope SEM and EDS analysis. The results showed of AuNPs/PSi heterojunction that the growth of the gold nanoparticles on porous silicon substrate have uniform and homogenous distribution and the formation of quasi-spherical AuNPs with a average dimeter of approximately 10 to 33 nm. Furthermore, the atoms ratio of gold nanoparticles increases with laser energy. The maximum value of Au atoms on porous silicon layer was found to be about0.94% atom at 500 mJ while the minimum values were found to be about 0.3%, 0.61% atom at 300mJ.and 4000mJ respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
31. Development of microfabricated planar slow-wave structures on dielectric substrates for miniaturized millimeter-band traveling-wave tubes.
- Author
-
Ryskin, Nikita M., Torgashov, Roman A., Starodubov, Andrey V., Rozhnev, Andrey G., Serdobintsev, Alexey A., Pavlov, Anton M., Galushka, Viktor V., Bessonov, Dmitry A., Ulisse, Giacomo, and Krozer, Viktor
- Subjects
SLOW wave structures ,TRAVELING-wave tubes ,MAGNETRONS ,DIELECTRICS ,LASER ablation ,MAGNETRON sputtering ,MICROSTRIP transmission lines - Abstract
We report the results of the design, simulation, fabrication, and cold-test measurements of millimeter-band 2D planar microstrip slow-wave structures (SWSs) on dielectric substrates. Such structures have a high slow-wave factor, which allows for low-voltage operation and reduction in the size and weight of the device. A low-cost and flexible fabrication technology based on magnetron sputtering and subsequent laser ablation has been developed and is reported in the paper. Microstrip meander-line SWS circuits at V-, W-, and D-bands have been fabricated and characterized. The fabrication of ring-bar planar SWSs by the photolithographic method is also discussed. Experimental measurement of S-parameters of the fabricated structures reveals good transmission properties. Return loss (S11) does not exceed −10 dB and attenuation is about 2 dB/cm in the V-band, 10 dB/cm in the W-band, and 8.5 dB/cm in the D-band. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
32. Measurement Issues In Pulsed Laser Propulsion.
- Author
-
Sinko, John E., Scharring, Stefan, Eckel, Hans-Albert, Röser, Hans-Peter, and Sasoh, Akihiro
- Subjects
LASER ablation ,PULSED laser deposition ,DATA analysis ,INDUSTRIAL engineering ,QUALITY control - Abstract
Various measurement techniques have been used throughout the over 40-year history of laser propulsion. Often, these approaches suffered from inconsistencies in definitions of the key parameters that define the physics of laser ablation impulse generation. Such parameters include, but are not limited to the pulse energy, spot area, imparted impulse, and ablated mass. The limits and characteristics of common measurement techniques in each of these areas will be explored as they relate to laser propulsion. The idea of establishing some standardization system for laser propulsion data is introduced in this paper, so that reported results may be considered and studied by the general community with more certain understanding of particular merits and limitations. In particular, it is the intention to propose a minimum set of requirements a literature study should meet. Some international standards for measurements are already published, but modifications or revisions of such standards may be necessary for application to laser ablation propulsion. Issues relating to development of standards will be discussed, as well as some examples of specific experimental circumstances in which standardization would have prevented misinterpretation or misuse of past data. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
33. Thermal modeling and experimental study of infrared nanosecond laser ablation of silicon.
- Author
-
Tao, Sha, Wu, Benxin, Zhou, Yun, and Gao, Yibo
- Subjects
SILICON ,LASER ablation ,MODELING (Sculpture) ,EVAPORATION (Chemistry) ,ULTRASHORT laser pulses - Abstract
Nanosecond (ns) laser ablation of silicon has important applications in electronics, photovoltaics, and many other areas. However, most of the previous work is mainly focused on ultraviolet (UV) or visible ns lasers, and the investigation is very limited for infrared lasers (e.g., at 1064 nm), which have the advantage of much lower cost and external energy consumption. In this paper, a thermal model has been developed and experimentally verified for ablation of silicon by 200 ns and 1064 nm laser pulses. This kind of work has been rarely reported in literature. The model predictions agree reasonably well with experimental measurements. The investigation indicates that surface evaporation should be the dominant physical mechanism of material removal for laser silicon ablation under the studied conditions. It has also been found that the physical processes of multipulse laser-silicon interaction at 1064 nm may strongly depend on laser pulse number and repetition rate (the pulse-to-pulse temporal distance). [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
34. Sphere-Wall Impact Experiments with Piezoelectric Force Sensors.
- Author
-
Sinko, John E. and Lassiter, Jonathan S.
- Subjects
CONFERENCES & conventions ,INDUSTRIAL lasers ,LASER ablation ,TACTILE sensors ,PIEZOELECTRICITY ,PIEZOELECTRIC devices - Abstract
Measurement of impulse imparted to a target from μs-timescale laser ablation events is often performed with piezoelectric force sensors. For pulsed laser ablation with a target resting on the force sensors, an effect can occur for a vertical thrust stand in an exhaust-up configuration that results in measurement of about twice the actual imparted impulse. A CO
2 laser operating at 10.6 μm wavelength, 300 ns pulse length, and up to 20 J pulse energy single shots was used to ablate samples of PCTFE. Force sensor measurements of the imparted impulse were compared to tests with a ballistic pendulum over a variety of fluences. The theoretical impulse delivered by the impacts of 6 mm diameter spheres of aluminum, steel, POM, and PTFE on the force sensor were studied, and the coefficients of restitution were measured for the targets. Practical issues for measurement of ablation-imparted impulse with piezoelectric sensors are discussed. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
35. Compact And Robust Laser Impulse Measurement Device, With Ultrashort Pulse Laser Ablation Results.
- Author
-
Kremeyer, Kevin, Lapeyre, John, and Hamann, Steven
- Subjects
CONFERENCES & conventions ,LASER ablation ,INDUSTRIAL lasers ,SPACE flight propulsion systems ,ROCKETRY - Abstract
An impulse measurement device and analysis package was conceived, designed, constructed, tested, and demonstrated to be capable of: measuring nanoNewton-seconds to milliNewton-seconds of impulse due to laser-ablation; being transported as carry-on baggage; set-up and tear-down times of less than an hour; target exchange times of less than two minutes (targets can be ablated at multiple positions for thousands of shots); measurements in air and in vacuum; error of just a few percent; repeatability over a wide range of potential systematic error sources; and time between measurements, including ring-down and analysis, of less than 30 seconds. The instrument consists of a cantilever (i.e. leaf spring), whose time-dependent displacement/oscillation is measured and analyzed to determine the impulse imparted by a laser pulse to a target. These shapes are readily/commercially available, and any target material can be used, provided it can be fashioned in the form of a cantilever, or as a coating/film/tape, suitable for mounting on a cantilever of known geometry. The instrument was calibrated both statically and dynamically, and measurements were performed on brass, steel, and Aluminum, using laser pulses of ∼7 ns, ∼500 ps, and ∼500 fs. The results agree well with those published in the literature, with surface effects, atmosphere, and pre-/post-pulses demonstrating interesting effects and indicating areas for further study. These parameters should be carefully controlled and held constant during a series of measurements. The impulse imparted by ablation due to laser filaments in air was also explored. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
36. Australian Science and Technology with Relevance to Beamed Energy Propulsion.
- Author
-
Froning, H. David
- Subjects
CONFERENCES & conventions ,PROPULSION systems ,INDUSTRIAL lasers ,LASER ablation ,LIGHT amplifiers - Abstract
Although Australia has no Beamed Energy Propulsion programs at the present time, it is accomplishing significant scientific and technological activity that is of potential relevance to Beamed Energy Propulsion (BEP). These activities include: continual upgrading and enhancement of the Woomera Test Facility, Which is ideal for development and test of high power laser or microwave systems and the flight vehicles they would propel; collaborative development and test, with the US and UK of hypersonic missiles that embody many features needed by beam-propelled flight vehicles; hypersonic air breathing propulsion systems that embody inlet-engine-nozzle features needed for beam-riding agility by air breathing craft; and research on specially conditioned EM fields that could reduce beamed energy lost during atmospheric propagation. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
37. First-Overtone CO Laser as a Potential Driver for Beamed Energy Propulsion.
- Author
-
Ionin, Andrey and Seleznev, Leonid
- Subjects
CONFERENCES & conventions ,INDUSTRIAL lasers ,LIGHT amplifiers ,LIGHT sources ,LASER ablation - Abstract
A possibility of application of a high-power first-overtone CO laser as a potential driver for beamed energy propulsion is discussed. The laser can operate within wavelength range ∼3.3–4.0 μm corresponding to the atmospheric transparency window. The laser efficiency was recently experimentally demonstrated to reach 16%, with theoretically predicted one being higher than 20%. A brief introduction into the first-overtone CO laser physics and information on progress in the R&D of such lasers are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
38. Liquid-fueled, Laser-powered, N-class thrust Space Engine with Variable Specific Impulse.
- Author
-
Phipps, Claude R., Luke, James R., and Helgeson, Wesley
- Subjects
CONFERENCES & conventions ,INDUSTRIAL lasers ,LASER ablation ,SPACE vehicle design & construction ,ASTRONAUTICS ,SPACE flight propulsion systems - Abstract
We discuss the requirements for developing a lightweight laser-powered space engine with specific impulse range 200sp<3,600 seconds and 6N maximum thrust. Operating parameters which can achieve this have been demonstrated separately in the laboratory. We review earlier solid fuel data. Such an engine can put small satellites through demanding maneuvers in short times, while generating the optimum specific impulse for each mission segment. We will address specific problems which have been solved. The first of these is fuel delivery to the laser focus. A pulsed laser format is required for reasons we will discuss. Solid-fuel configurations (such as the fuel tapes used in the Photonic Associates μLPT microthruster) are not amenable to the range of mass delivery rates (μg/s to mg/s) necessary for such an engine. Liquid fuels are suggested. However, liquids with ordinary viscosities splash under pulsed laser illumination, ruining engine performance by causing the majority of fuel mass to be ejected at low I
sp . We have shown that Isp = 680 seconds can be achieved by a viscous fuel based on glycidyl azide polymer and an IR-dye laser absorber. The second problem is optics clouding from ablated material. This can be handled actively by a flowing gas system. The final problem is mass: we will present an engine design which fits within a 10-kg “dry mass” budget. The engine, 80 kg mass with fuel, is designed to fit within a 180-kg spacecraft, and use up 3 kW of prime power to deliver a Δv of 17.5 km/s to the spacecraft in sixteen months. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
39. Constant-Fluence Area Scaling for Laser Propulsion.
- Author
-
Sinko, John E.
- Subjects
CONFERENCES & conventions ,LASER ablation ,INDUSTRIAL lasers ,SCATTERING (Physics) ,SCALING laws (Statistical physics) ,POLYOXYMETHYLENE - Abstract
A series of experiments was conducted on polyoxymethylene (POM, trade name Delrin®) propellants in air at atmospheric pressure. A TEA CO
2 laser with maximum output power up to 20 J was used to deliver 300 ns pulses of 10.6 μm radiation to POM targets. Ablation at a constant fluence and a range of spot areas was achieved by varying combinations of the laser energy and spot size. Relevant empirical scaling laws governing laser propulsion parameters such as the momentum coupling coefficient (Cm ) and specific impulse (Isp ) for spot areas within a range of about 0.05–0.25 cm2 are presented. Experimental measurements of imparted impulse, Cm , Isp , and ablated mass per pulse were made using dynamic piezoelectric force sensors and a scientific balance. Finally, Schlieren ICCD imaging of shock waves and vapor plumes was performed and analyzed. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
40. Laser Propulsion with Liquid Propellants Part II: Thin Films.
- Author
-
Sinko, John E., Dhote, Nilesh B., and Pakhomov, Andrew V.
- Subjects
CONFERENCES & conventions ,INDUSTRIAL lasers ,LASER ablation ,ROCKET fuel ,PROPELLANTS ,LIQUID propellants - Abstract
Thin films of a liquid propellant have been studied as a potential way to boost thrust for laser propulsion applications. A TEA CO
2 laser with 300 ns pulse width was operated at up to 20 J pulse energy to produce irradiances at the target on the order of 1–1200 MW/cm2 to ablate various systems of thin films on Delrin® substrates. In this study, time-resolved force sensors and ICCD imaging techniques were used to determine how an addition of thin liquid films to solid substrates affects propulsive properties such as momentum coupling coefficient, specific impulse, and internal efficiency. Transparent (hexane) and absorbing (ethanol and water) thin films were formed above Delrin® substrates for the laser system operating at 10.6 μm. Thickness effects on the hexane-Delrin® system will be examined. An analysis will be made of the possible routes for force generation, and the general properties, benefits, and shortcomings of liquid thin film structures will be summarized with regard to laser propulsion. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
41. Diagnostics and Impulse Performance of Laser-Ablative Propulsion.
- Author
-
Sasoh, Akihiro, Mori, Koichi, Anju, Kohei, Suzuki, Koji, Shimono, Masaya, and Sawada, Keisuke
- Subjects
CONFERENCES & conventions ,LASER ablation ,INDUSTRIAL lasers ,LASER beams ,FORCE & energy ,PRESSURE - Abstract
Pressure time variations and associated flows induced by pulsed laser ablation were experimentally studied using the Velocity Interferometer System for Any Reflector (VISAR) and framing Schlieren visualization. The combination of either aluminum or polyacetal target and TEA CO
2 laser pulse were examined. The VISAR measurement resolved that the pressure modulated from the laser power variation in the impulse generation processes. Integrated impulse induced by repetative CO2 laser pulses was measured using a torsion-type impulse balance. The effect of the ambient pressure was significant. The measured impulse characteristics were closely associated with target surface morphology and fluid dynamics. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
42. Binary Solid Propellants for Constant Momentum Missions.
- Author
-
Pakhomov, Andrew V. and Mahaffy, Kevin E.
- Subjects
CONFERENCES & conventions ,AERONAUTICS ,LASER ablation ,INDUSTRIAL lasers ,MANUFACTURING processes - Abstract
A constant momentum mission is achieved when the speed of the vehicle in the inertial frame of reference is equal to the speed of exhaust relative to the vehicle. Due to 100% propulsive efficiency such missions are superior to traditional constant specific impulse missions. A new class of solid binary propellants for constant momentum missions is under development. A typical propellant column is prepared as a solid solution of two components, with composition gradually changing from 100% of a propellant of high coupling coefficient (C
m ) to one which has high specific impulse (Isp ). The high coupling component is ablated first, gradually giving way to the high Isp component, as the vehicle accelerates. This study opens new opportunities for further design of complex propellants for laser propulsion, providing variable Cm and Isp during missions. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
43. Laser Power Beaming On A Shoestring.
- Author
-
Kare, Jordin T. and Nugent, Thomas J.
- Subjects
CONFERENCES & conventions ,INDUSTRIAL lasers ,POWER (Mechanics) ,LASER ablation - Abstract
The NASA Centennial Challenge for Power Beaming is a prize offered for a competitive demonstration of wireless power transmission. The minimum viable competition entry for 2007 was required to deliver greater than 200 watts to a moving 10-kilogram vehicle over a vertical distance of 100 meters. We describe the design, construction, and operation of a laser power transmission system which considerably exceeds these minimum requirements, and which was built by a largely non-professional team with minimal financial support in less than one year. The system uses commercially-available 808 nm diode arrays and simple optics to produce a multikilowatt beam, approximately 1×0.6 m. An automated video tracking system with manual backup and a 1 m
2 steerable mirror direct the beam. The receiver is assembled from two types of GaAs photovoltaic cells in a unique configuration. Overall, the system could deliver in excess of 1 kW of DC power to a vehicle with an end to end efficiency of well over 10%, but due to inadequate testing and on-site failures, it failed to win the 2007 prize. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
44. Laser ablation of a platinum target in water. II. Ablation rate and nanoparticle size distributions.
- Author
-
Nichols, William T., Sasaki, Takeshi, and Koshizaki, Naoto
- Subjects
NANOPARTICLES ,LASER ablation ,PLATINUM ,PARTICLE size determination ,OPTICAL properties of particles - Abstract
This is the second in a series of three papers examining nanomaterial formation in laser ablation in liquids (LAL). Here we study the effect of the laser wavelength and fluence on the mass yield and size distribution of nanoparticles prepared by laser ablation of a platinum target immersed in water. For all wavelengths tested, laser fluences in the range of 10–70 J/cm
2 resulted in spheroidal, nonagglomerated platinum nanoparticles with sizes ranging from 1 to 30 nm. Nanoparticle size distributions are found to be composed of two modes that are attributed to thermal vaporization and explosive boiling mechanisms. The peak of the smaller size mode remains nearly constant at 3 nm for all laser conditions, which is suggested to be due to the strong confinement of the vapor plume by the liquid. The larger size mode peaks in the range of 5–15 nm with a population that is strongly dependent on the laser parameters. It is concluded that changes in the mean size reported in many earlier studies on LAL of metal targets are a result of the relative quantity of nanoparticles from each mechanism rather than direct control over the ablation process. Additionally, it was observed that the yield of platinum nanoparticles was significantly larger for 1064 nm wavelength at fluences greater than 10 J/cm2 . The maximum ablation rate was approximately 4.4 mg/h, with an estimated ablation and collection efficiency of 0.9 μg/J. Dependence of the mass yield on wavelength and fluence is seen to be dependent primarily on the extent of the explosive mechanism. [ABSTRACT FROM AUTHOR]- Published
- 2006
- Full Text
- View/download PDF
45. Laser ablation of a platinum target in water. III. Laser-induced reactions.
- Author
-
Nichols, William T., Sasaki, Takeshi, and Koshizaki, Naoto
- Subjects
LASER ablation ,INDUSTRIAL lasers ,PLATINUM ,NANOPARTICLES ,PLASMA etching - Abstract
This is the third paper in our series studying the laser-target-liquid interactions occurring in laser ablation in liquids (LAL). Here, laser ablation of a platinum target in pure water at 355 nm wavelength is studied as a function of laser energy. We describe three distinct reaction regimes between the ablated target species and water at different laser focusing conditions. At low laser fluence (<10 J/cm
2 ), material removal is caused by laser heating of the platinum surface and the primary products are small clusters with a large percentage of platinum atoms in a nonzero oxidation state. At intermediate fluences (10–70 J/cm2 ), platinum nanoparticles are the primary products. Our previous studies demonstrated that in this fluence regime ablation occurs through both thermal vaporization and explosive ejection of molten droplets. In both cases reactivity is small due to the low reactivity of platinum with water. At high fluences (>70 J/cm2 ), we find large, faceted particles that are attributed to the drying of PtOx gels formed by reactive plasma etching of the target. Taken together these results demonstrate that significant tunability in the target-liquid interaction is possible during nanomaterial synthesis by LAL. [ABSTRACT FROM AUTHOR]- Published
- 2006
- Full Text
- View/download PDF
46. Laser ablation of a platinum target in water. I. Ablation mechanisms.
- Author
-
Nichols, William T., Sasaki, Takeshi, and Koshizaki, Naoto
- Subjects
LASER ablation ,SURFACE roughness ,PLATINUM ,NANOPARTICLES ,WAVELENGTHS - Abstract
This is the first in a series of three papers aimed at better understanding the processes that lead to nanomaterial formation during laser ablation of solid targets in liquids. Here we study the variation of the target surface morphology versus laser fluence and wavelength in order to suggest an ablation mechanism. A key finding is that an explosive ablation mechanism is prominent for a wide range of laser fluences for all wavelengths tested. Interestingly, however, ultraviolet (355 nm) and infrared (1064 nm) wavelengths show characteristically different explosive behaviors. In the infrared case, numerous large craters with diameters around 20 μm form at localized points within the laser irradiated area. In contrast, ultraviolet ablation results in a striking transition to nanoscale surface roughness across the entire irradiated area. This texture is attributed to spinodal decomposition at the molten target surface. We propose that the wavelength and fluence dependence of the ablation craters can be explained by the amount of energy absorbed in the target. The consequences of the ablation mechanism for nanomaterial synthesis are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
47. A mathematical description of surface texture development in laser-ablated dentin.
- Author
-
Oliveira, V., Sivakumar, M., and Vilar, R.
- Subjects
SURFACES (Physics) ,LASER ablation ,DENTIN ,EXCIMER lasers ,MATHEMATICAL models ,TESSELLATIONS (Mathematics) ,ULTRASHORT laser pulses - Abstract
A cone-shaped texture is observed when a transverse cross section of human dentin cut perpendicularly to the tooth axis is processed with KrF excimer laser radiation using appropriate processing parameters. In the present paper, a mathematical model describing the kinetics of cone growth as a function of the number of laser pulses is presented. It is shown that the fractional area occupied by cones is adequately described by a modified Johnson-Mehl-Avrami-Kolmogorov equation and that the boundary lines between cones define a Voronoi tessellation generated from the corresponding initial tubule location. This model allows the surface texture evolution in dentin to be predicted from the initial tubule distribution. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
48. Optimization of micropore fabrication on the surface of ultrathick polyimide film based on picosecond UV laser.
- Author
-
Liu, Haixing, Xu, Jie, He, Haojian, Wu, Chao, Liu, Jing, He, Xiuquan, and Wang, Xizhao
- Subjects
POLYIMIDE films ,HIGH power lasers ,ULTRAVIOLET lasers ,THIN films ,POLYMER films ,LASER ablation - Abstract
Micropores fabricated on organic polymer films have a wide range of applications in fields such as microfiltration, new energy, and biomedical separation. The use of laser processing technology can complete the processing of micropores on the surface of ultrathin films with high precision, but there is still some difficulty in the processing of ultrathick films. In this paper, a picosecond ultraviolet (UV) laser was used to explore the high-precision manufacturing process of micropores on the surface of ultrathick polyimide (PI) films. The effects of laser power, laser frequency, and scanning speed on the cone angle and spatter deposition area of micropores' fabrication on ultrathick PI were studied based on orthogonal experiments. The mechanism of processing micropores on ultrathick PI was analyzed by studying the deposition area and morphology of the spatter generated during the laser ablation process. It was found that high-quality micropores can be fabricated at low laser frequency and high power. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
49. The influences of surface plasmons and thermal effects on femtosecond laser-induced subwavelength periodic ripples on Au film by pump-probe imaging.
- Author
-
Kan Zhou, Xin Jia, Tianqing Jia, Ke Cheng, Kaiqiang Cao, Shian Zhang, Donghai Feng, and Zhenrong Sun
- Subjects
SURFACE plasmons ,FEMTOSECOND lasers ,GOLD films ,LASER ablation ,SOLIDIFICATION ,POLARITONS ,ELECTRON-phonon interactions - Abstract
In this paper, the influences of surface plasmons and thermal effects on the formation of subwavelength periodic ripples on Au films irradiated by 800nm femtosecond laser pulses were studied by collinear pump-probe imaging. The spatial and temporal resolutions of the experiment were 300 nm and 1 ps, respectively. No periodic ripples were observed on the Au film during ablation by the first pump pulse, but during ablation by the second pump pulse the appearance of transient ripples was evident from a delay time of hundreds of picoseconds to several nanoseconds. These ripples, however, were not retained after solidification. When the sample was immersed in water during ablation, however, the ripples were retained. It is proposed that, during the second laser pulse irradiation, the surface defects produced by the first pulse induced surface plasmon polaritons on the Au film, which caused a modulated energy deposition and the formation of transient ripples. The weak electron-phonon coupling and significant residual heat erase these ripples after the molten surface was solidified. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
50. Dispersed fluorescence spectroscopy of the SiCN Ã ²Δ - X ²Π system: Observation of some vibrational levels with chaotic characteristics.
- Author
-
Masaru Fukushimaa and Takashi Ishiwata
- Subjects
FLUORESCENCE spectroscopy ,SILICON compounds ,VIBRATIONAL spectra ,CHAOS theory ,LASER ablation ,PHASE transitions - Abstract
The laser induced fluorescence (LIF) spectrum of the à ²Δ - X ²Π transition was obtained for SiCN generated by laser ablation under supersonic free jet expansion. The vibrational structures of the dispersed fluorescence (DF) spectra from single vibronic levels (SVL's) were analyzed with consideration of the Renner-Teller (R-T) interaction. Analysis of the pure bending (ν
2 ) structure by a perturbation approach including R-T, anharmonicity, spin-orbit (SO), and Herzberg-Teller (H-T) interactions indicated considerably different spin splitting for the μ and ? levels of the X ²Π state of SiCN, in contrast to identical spin splitting for general species derived from the perturbation approach, where μ and ? specify the lower and upper levels, respectively, separated by R-T. Further analysis of the vibrational structure including R-T, anharmonicity, SO, H-T, Fermi, and Sears interactions was carried out via a direct diagonalization procedure, where Sears resonance is a second-order interaction combined from SO and H-T interactions with ΔK = ±1, Δ∑ = ±1, and ΔP = 0, and where P is a quantum number, P = K + ∑. The later numerical analysis reproduced the observed structure, not only the pure ν2 structure but also the combination structure of the ν2 and the Si-CN stretching (ν3 ) modes. As an example, the analysis demonstrates Sears resonance between vibronic levels, (01¹0) ? ∑(+) and (020 0) μ Π½ , with ΔK = ±1 and ΔP = 0. On the basis of coefficients of their eigen vectors derived from the numerical analysis, it is interpreted as an almost one-to-one mixing between the two levels. The mixing coefficients of the two vibronic levels agree with those obtained from computational studies. The numerical analysis also indicates that some of the vibronic levels show chaotic characteristics in view of the two-dimensional harmonic oscillator (2D-HO) basis which is used as the basis function in the present numerical analysis; i.e., the eigen vectors for some of the observed levels have several components of the basis, and we have not been able to give precise vibronic assignments for the levels, but just vibronically labeled, referring the largest component in their vectors. (To emphasize this situation, we do not use the word "assignment," but prefer to use "label" as the meaning of just "label," but not "assign," throughout this paper.) The latter shows that the vibronic labels of the levels are meaningless, and the P quantum number and the order of their eigen states in the P matrix block derived in the numerical analysis only characterize the vibronic levels. Comparing the constants obtained for all of the interactions with those of species showing Sears resonance and studied previously, it is found that none of them are strong, but are moderate. It is thus concluded that the chaotic appearance is not derived by any strong interaction, but is induced by complex and accidental proximities of the vibronic levels caused by the moderate interactions. [ABSTRACT FROM AUTHOR]- Published
- 2016
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