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David A Willis - One of the best experts on this subject based on the ideXlab platform.
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validity of the taylor sedov theory for studying laser induced Phase Explosion and shock waves
Journal of Nanoscience and Nanotechnology, 2015Co-Authors: Mohammad Hendijanifard, David A WillisAbstract:: Phase Explosion is a Phase change process that occurs during short pulse laser ablation. Phase Explosion is a result of homogeneous nucleation of vapor in the superheated melt and results in a rapid transition from a superheated melt to a mixture of vapor and liquid droplets that expand from the surface. The sudden Phase transition results in rapid material removal, and if occurring in an ambient gas, causes a shock wave to propagate away from the surface. Measurements of this shock wave are commonly used with the Taylor-Sedov blast wave theory to estimate shock wave pressure and temperature. At low laser fluences the Mach number of the shock wave can be small, resulting in significant errors in pressure and temperature. The paper will demonstrate conditions for which the more general form of the Rankine-Hugoniot relations for thermo-fluid parameters simplifies to the Taylor-Sedov similarity solutions and when the Taylor-Sedov solutions are applicable. The results are compared to experimental shock wave data from the literature to explain why using the Taylor-Sedov blast wave solutions can result in large errors at low Mach numbers.
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time resolved dynamics of nanosecond laser induced Phase Explosion
Journal of Physics D, 2009Co-Authors: Cristian Porneala, David A WillisAbstract:Visualization of Nd : YAG laser ablation of aluminium targets was performed by a shadowgraph apparatus capable of imaging the dynamics of ablation with nanosecond time resolution. Direct observations of vaporization, explosive Phase change and shock waves were obtained. The influence of vaporization and Phase Explosion on shock wave velocity was directly measured. A significant increase in the shock wave velocity was observed at the onset of Phase Explosion. However, the shock wave behaviour followed the form of a Taylor–Sedov spherical shock below and above the explosive Phase change threshold. The jump in the shock wave velocity above Phase Explosion threshold is attributed to the release of stored enthalpy in the superheated liquid surface. The energy released during Phase Explosion was estimated by fitting the transient shock wave position to the Taylor scaling rules. Results of temperature calculations indicate that the vapour temperature at the Phase Explosion threshold is slightly higher than the critical temperature at the early stages of the shock wave formation. The shock wave pressure nearly doubled when transitioning from normal vaporization to Phase Explosion.
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Phase Explosion and Marangoni flow effects during laser micromachining of thin metal films
Proceedings of SPIE, 2008Co-Authors: Mohammad Hendijanifard, David A WillisAbstract:Phase Explosion and Marangoni flow during laser micromachining of thin metal films are studied in this paper. The purpose of this study was to improve understanding of the time scales by which these processes occur. The study was based on a time-resolved reflection imaging method. The method used a nitrogen-pumped dye laser to illuminate the surface of the films at a given time after the Nd:YAG laser heats the film. The dye laser irradiation reflected from the surface was then imaged by a CCD camera. The lasers were coupled by a digital pulse-delay generator, allowing the time delay between the two lasers to be controlled by the user. The effects of Marangoni flow and Phase Explosion can be seen on the starting and ending times of ablation. At all fluences in the study, holes were opened in the aluminum films and the hole formation process was completed in under 350 ns. Ablation of nickel films was very different however, with thin layers of the film surface removed at low fluences, a process which took on the order of microseconds to complete. At higher fluences the nickel films ruptured and the hold opening process was completed in less than 500 ns.
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Laser-Induced Melting and Phase Explosion in Liquid Metal Films
ASME 2008 6th International Conference on Nanochannels Microchannels and Minichannels, 2008Co-Authors: Jill Klentzman, Vladimir S. Ajaev, David A WillisAbstract:We develop a mathematical model of liquid flow and Phase change phenomena during fabrication of micro- and nanochannels by laser-induced melting and evaporation of thin metal films deposited on glass substrates. Channels of cross-sectional sizes between several hundred nanometers and a few micrometers can be manufactured by wet etching or contact photolithography after the desired pattern is created by the laser in the metal film. Interaction of the laser beam with the metal film is a complicated process, characterized by high temperature gradients. In this work we investigate the regime where Phase Explosion takes place in a small region of the metal film surrounded by a pool of molten metal. In the melt region, both evaporation from the surface and viscous flow induced by thermocapillary stresses take place; all these processes are incorporated into the model. Evolution of the surface of the molten film is investigated, and the impact of Phase Explosion on the flow is discussed.© 2008 ASME
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Time-resolved imaging of explosive Phase change in metals
Proceedings of SPIE, 2007Co-Authors: Cristian Porneala, David A WillisAbstract:ABSTRACT Phase Explosion is a non-equilibrium boiling process resulting from homogeneous vapor nucleation in a superheated liquid near the critical point. Phase Explosion may occur during nanosecond laser ablation since heterogeneous nuclei responsible for normal boiling do not have sufficient time to grow. Understanding the explosive Phase change process is critical for developing models of material removal, and requires time-resolved diagnostics. A time-resolved shadowgraph technique was developed which was capable of probing ablation with nanosecond time exposures and nanosecond time delay resolution. Experiments were performed to investigate the transition from normal surface vaporization to Phase Explosion during nanosecond laser ablati on of aluminum and nickel. The threshold nature of Phase Explosion was observed by a discontinuous jump in the ablation depth at fluences of approximately 5.2 J/cm 2 and 6.9 J/cm 2 for aluminum and nickel, respectively. Shadowgraph images captured weak vaporization and shock waves below the threshold. At higher fluences, large droplets and vapor were observed as a result of Phase Explosion. The Phase Explosion process began shortly after the end of the laser pulse, consistent with existing estimates of homogeneous nucleation time lags in the research literature. Shock wave propagation was consistent with Taylor scaling below and above the Phase Explosion threshold. Keywords: Phase Explosion, nanosecond, laser ablation, micromachining, homogeneous nucleation
S I Kudryashov - One of the best experts on this subject based on the ideXlab platform.
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Double-pulse femtosecond laser ablation of the surface of stainless steel with variable interpulse delays
JETP Letters, 2016Co-Authors: E. I. Ageev, S I Kudryashov, A A Ionin, V. Yu. Bychenkov, V. P. Veiko, A. A. Petrov, A. A. SamokhvalovAbstract:Spectral studies of optical emission from plumes produced via ablation of the surface of stainless steel in the Phase Explosion regime at different incident fluences by a pair of collinear degenerate femtosecond laser pulses, separated by variable delay time of 0.01–1.5 ns, demonstrate a drastic decrease in atomic emission intensities in a subnanosecond range. This effect was related to “bulk” absorption of the second pump pulse in ablative plumes with near-critical density, achieved during their hydrodynamic expansion on a subnanosecond timescale.
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Multi-scale fluence-dependent dynamics of front-side femtosecond laser heating, melting and ablation of thin supported aluminum film
International Journal of Heat and Mass Transfer, 2016Co-Authors: S I Kudryashov, Andrey A. IoninAbstract:Abstract Optically thick, thermally thin aluminum film was homogeneously pumped by single IR femtosecond laser pulses at variable local fluences, resulting in its electronic excitation, electron-lattice energy transfer, melting, thermal expansion, ablative spallation and supercritical hydrodynamic expansion, probed by low-fluence UV femtosecond laser pulses at different – sub-picosecond, picosecond and sub-nanosecond – timescales. Fluence dependences of their corresponding key dynamic parameters – peak electronic temperature, internal melt temperature and pressure, volume energy density present in the film on different time scales upon different dissipative processes, spallation and Phase Explosion temperatures, their onset times, lift-off speeds and crater depths were measured for aluminum for the first time. These dependences indicate sub-nanosecond and picosecond onsets of spallation and Phase Explosion in the film, as well as their occurrence near the boiling and critical temperatures, respectively. Significant difference in energy density magnitudes, primarily absorbed from the laser radiation and subsequently deposited into electronic and ion sub-systems, was revealed and related preferably to prompt charge emission, reducing the peak transient electron temperature, and evaporative surface cooling of the molten material.
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Single-shot front-side nanoscale femtosecond laser ablation of a thin silver film
Applied Physics A, 2014Co-Authors: P. A. Danilov, S I Kudryashov, A A Ionin, E. A. Drozdova, S. B. Odinokov, A. A. Rudenko, V. I. Yurovskikh, D. A. ZayarnyAbstract:Nano- and microscale holes, as well as related sub-ablative nanospikes and sub-micron bumps, were produced in a 30-nm thick silver film on a silica substrate by single femtosecond laser pulses with variable pulse energies, focused by different strong focusing optics. Characteristic laser energy deposition dimensions exceed the expected focal spots by nearly 2 microns, indicating the considerable lateral thermal transport in the film, while the effective hole formation thresholds decrease versus increasing numerical aperture of focusing optics. Morphologies of the sub-ablative solidified surface nanostructures and numerical estimates of deposited volume energy density undermine blowing-off the molten film due to subsurface boiling and near-critical Phase Explosion at lower and higher sub-threshold fluences, respectively.
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dynamics of laser induced surface Phase Explosion in silicon
Applied Physics Letters, 2011Co-Authors: S I Kudryashov, Stanley Paul, Kevin Lyon, Susan D AllenAbstract:Time-resolved ultrasonic studies revealed a second, delayed ablative pressure pulse after the first primary plasma pressure pulse in a silicon wafer irradiated by a UV nanosecond laser. The intensity-dependent delay time for the second pulse indicates the existence of a corresponding intensity-dependent homogeneous vapor bubble nucleation time in the superheated molten silicon prior to its Phase Explosion and ablative removal, since the integral pressure correlates with the ablation rate. A transient hot ablative plasma with calculated peak temperature ∼30–90 eV and pressure ∼20–110 GPa is suggested to superheat the bulk silicon via short-wavelength recombination and Bremsstrahlung emission.
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near critical nanosecond laser induced Phase Explosion on graphite surface
Applied Physics A, 2011Co-Authors: S I Kudryashov, A A Tikhov, V D ZvorykinAbstract:Optical reflectivity, removal rate and ablative recoil pressure magnitudes were measured as a function of laser fluence during high-power UV nanosecond laser ablation of graphite. At low fluences only melting and weak surface vaporization of molten carbon were observed. At moderate fluences there is a very narrow fluence interval where the reflected fluence starts to saturate, while the removal rate and ablative recoil pressure rise drastically in a correlated manner, indicating the onset of a near-critical surface Phase Explosion. Then, at higher fluences the reflected fluence, removal rate and recoil pressure saturate with an appearance of a luminous plume, altogether indicating negligible specular reflectance and absorbance on the target surface due to its complete screening by the highly-absorbing laser plume. The overall strong correlation between the removal rate and recoil pressure magnitudes may indicate rather quasi-continuous removal of the near-critical superheated molten carbon layer by a propagating unloading wave in the absence of a crucial sub-surface temperature maximum in the layer.
Quanming Lu - One of the best experts on this subject based on the ideXlab platform.
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theory analysis of wavelength dependence of laser induced Phase Explosion of silicon
Journal of Applied Physics, 2008Co-Authors: Quanming Lu, Richard E RussoAbstract:large micron-sized particulates were observed to eject from the target about 300–400 ns after the laser pulse. In contrast, for 1064 nm pulse, this dramatic increase was not observed. The underlying mechanism for the observed threshold phenomenon is presented in this study, which can be attributed to the thermal diffusion and subsequent explosive boiling after the completion of the interaction between the nanosecond laser pulse and silicon. Based on our delayed Phase explosive model, the ablation depths were calculated for different wavelengths and compared to experimental results. Plasma shielding during laser irradiation was included in the model, which plays a key role to the coupling of laser energy to the irradiated material. © 2008 American Institute of Physics. DOI: 10.1063/1.2978369
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Thermodynamic evolution of Phase Explosion during high-power nanosecond laser ablation.
Physical review. E Statistical nonlinear and soft matter physics, 2003Co-Authors: Quanming LuAbstract:It is argued that Phase Explosion plays an important role during high-power laser ablation. A theoretical model which includes the effect of an expanding mass plasma has been developed to describe the process of Phase Explosion during the interactions of a high-power nanosecond laser pulse on an aluminum target. For a laser with a 3-ns pulse duration, if the laser intensity is high enough (>or=5 x 10(10) W/cm(2)), Phase Explosion was found to occur after the completion of the laser pulse, but not during the process of laser energy deposition. This result is consistent with recent experiments. It is also found that the pressure of the induced ablation plasma plays a crucial role in the process of Phase Explosion.
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thermodynamic evolution of Phase Explosion during high power nanosecond laser ablation
Physical Review E, 2003Co-Authors: Quanming LuAbstract:Laser ablation is a process whereby materials are removed from the surface of a solid by laser irradiation. It is finding applications in a growing number of areas, such as deposition of metal and dielectric films and laser ablation chemical analysis @1#. Laser ablation is also of great interest from a basic physical point of view. Its fundamental mechanisms are not fully understood, especially when high-power laser pulses are utilized and superheating of the target material occurs. Miotello and Kelly suggested that when the laser irradiance is sufficiently high so that the target surface reaches a temperature ;0.9TC (TC is the thermodynamic critical temperature!, Phase Explosion might be a mechanism that removes materials from the laser-ablated target @2,3# .I n this process, homogeneous bubble nucleation occurs, and the target makes a rapid transition from a superheated liquid layer to a mixture of vapor and liquid droplets, which then eject from the target surface. These authors suggested that for high-power nanosecond laser pulse, Phase Explosion occurs during the laser pulse. However, recently experimental results using a Nd:YAG laser pulse with a 3-ns pulse duration on a silicon target revealed that Phase Explosion would occur after the completion of the laser pulse @4,5#. The theory of Phase Explosion may be considered from either a kinetic or a thermodynamic viewpoint. The former models the rate and the probability of vapor bubble formation at any temperature, while the latter provides a rigorous method by which to predict the limit of superheated liquid @6#. According to kinetic theory, when the liquid is superheated, homogeneous bubble nucleation occurs. If these bubbles reach a critical radius r c , they will grow spontaneously. Bubbles with a radius less than r c are likely to collapse. When the radii of a definite number of bubbles are larger than r c , Phase Explosion will happen @7,8#. Based on this kinetic theory, Lu et al. demonstrated that Phase Explosion can occur after the completion of the laser pulse provided the pulse is sufficiently short ~,tens of ns !@ 9#. While various models have been developed to study the Phase Explosion during ultrafast laser ablation @10#, relatively little attention has been paid to mechanisms of Phase Explosion for high-power nanosecond laser pulse. In this paper, using a one-dimensional fluid model we calculate the thermodynamic process of Phase Explosion during nanosecond laser ablation of an Al target. The model results are consistent with those from the kinetic theory as well as the experimental results, which indicate that Phase Explosion occurs after the completion of the laser pulse. Since its thermal and optical properties are well characterized, aluminum is selected as the target material @11‐13#. The ablation laser pulse for the simulation is a 532-nmwavelength Gaussian beam with 3 ns full width at half maximum ~FWHM!. Initially, the semi-infinite Al target is set at its melting point, whose mass density and temperature are 2.7 g/cm 2 and 933 K, respectively. According to Ref. @14#,
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Thermal model of Phase Explosion for high-power laser ablation
High-Power Laser Ablation IV, 2002Co-Authors: Quanming Lu, Richard E RussoAbstract:Although laser ablation of solid materials is finding applications in a growing number of fields, the basic mechanisms underlying laser ablation processes have not been fully understood. One fundamental parameter for high-power laser ablation applications is the ablation depth resulting from the interaction of individual laser pulses. The ablation depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 20 GW/cm 2 . Above this threshold, micron-sized particulates have been observed to eject from the target surface. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of laser irradiation is a possible mechanism to describe the observed dramatic increase of the ablation depth. Calculations based on this delayed Phase Explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation plays an important role on this threshold phenomenon.
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delayed Phase Explosion during high power nanosecond laser ablation of silicon
Applied Physics Letters, 2002Co-Authors: Quanming Lu, Richard E RussoAbstract:An important parameter for high-irradiance laser ablation is the ablation crater depth, resulting from the interaction of individual laser pulses on a targeted surface. The crater depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 2×1010 W/cm2, above which, large (micron-sized) particulates were observed to eject from the target. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of the laser pulse is a possible mechanism for the observed dramatic increase of the ablation depth. Calculations based on this delayed Phase Explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation has a profound effect on this threshold phenomenon.
Cristian Porneala - One of the best experts on this subject based on the ideXlab platform.
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time resolved dynamics of nanosecond laser induced Phase Explosion
Journal of Physics D, 2009Co-Authors: Cristian Porneala, David A WillisAbstract:Visualization of Nd : YAG laser ablation of aluminium targets was performed by a shadowgraph apparatus capable of imaging the dynamics of ablation with nanosecond time resolution. Direct observations of vaporization, explosive Phase change and shock waves were obtained. The influence of vaporization and Phase Explosion on shock wave velocity was directly measured. A significant increase in the shock wave velocity was observed at the onset of Phase Explosion. However, the shock wave behaviour followed the form of a Taylor–Sedov spherical shock below and above the explosive Phase change threshold. The jump in the shock wave velocity above Phase Explosion threshold is attributed to the release of stored enthalpy in the superheated liquid surface. The energy released during Phase Explosion was estimated by fitting the transient shock wave position to the Taylor scaling rules. Results of temperature calculations indicate that the vapour temperature at the Phase Explosion threshold is slightly higher than the critical temperature at the early stages of the shock wave formation. The shock wave pressure nearly doubled when transitioning from normal vaporization to Phase Explosion.
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Time-resolved imaging of explosive Phase change in metals
Proceedings of SPIE, 2007Co-Authors: Cristian Porneala, David A WillisAbstract:ABSTRACT Phase Explosion is a non-equilibrium boiling process resulting from homogeneous vapor nucleation in a superheated liquid near the critical point. Phase Explosion may occur during nanosecond laser ablation since heterogeneous nuclei responsible for normal boiling do not have sufficient time to grow. Understanding the explosive Phase change process is critical for developing models of material removal, and requires time-resolved diagnostics. A time-resolved shadowgraph technique was developed which was capable of probing ablation with nanosecond time exposures and nanosecond time delay resolution. Experiments were performed to investigate the transition from normal surface vaporization to Phase Explosion during nanosecond laser ablati on of aluminum and nickel. The threshold nature of Phase Explosion was observed by a discontinuous jump in the ablation depth at fluences of approximately 5.2 J/cm 2 and 6.9 J/cm 2 for aluminum and nickel, respectively. Shadowgraph images captured weak vaporization and shock waves below the threshold. At higher fluences, large droplets and vapor were observed as a result of Phase Explosion. The Phase Explosion process began shortly after the end of the laser pulse, consistent with existing estimates of homogeneous nucleation time lags in the research literature. Shock wave propagation was consistent with Taylor scaling below and above the Phase Explosion threshold. Keywords: Phase Explosion, nanosecond, laser ablation, micromachining, homogeneous nucleation
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observation of nanosecond laser induced Phase Explosion in aluminum
Applied Physics Letters, 2006Co-Authors: Cristian Porneala, David A WillisAbstract:The transition from normal vaporization to Phase Explosion during laser ablation of aluminum was investigated using a nanosecond Nd:YAG laser. The threshold nature of Phase Explosion was observed by a discontinuous jump in the ablation depth at approximately 5.2J∕cm2. Ablation was imaged using a shadowgraph technique that was capable of probing ablation with nanosecond exposure time and nanosecond time delay resolution with respect to laser heating. Images above the threshold captured a mixture of vapor and droplets generated by Phase Explosion, which began near the end of the laser pulse without a significant time lag.
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effect of the dielectric transition on laser induced Phase Explosion in metals
International Journal of Heat and Mass Transfer, 2006Co-Authors: Cristian Porneala, David A WillisAbstract:Abstract Phase Explosion is an explosive liquid to vapor Phase change that occurs during laser ablation as the surface approaches 90% of the thermodynamic critical temperature (0.9Tc), which is the upper limit of superheating. Large variations in properties are expected to occur near 0.8Tc, transforming the electrically conductive metal into a nearly transparent dielectric, an effect that has been neglected in previous models of laser ablation. The work presented in this paper numerically investigates the possible effect of the dielectric transition using a one dimensional heat transfer model. The results show that accurate knowledge of the absorption coefficient above 0.8Tc is critical for predicting the laser fluence at which Phase Explosion occurs.
Richard E Russo - One of the best experts on this subject based on the ideXlab platform.
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theory analysis of wavelength dependence of laser induced Phase Explosion of silicon
Journal of Applied Physics, 2008Co-Authors: Quanming Lu, Richard E RussoAbstract:large micron-sized particulates were observed to eject from the target about 300–400 ns after the laser pulse. In contrast, for 1064 nm pulse, this dramatic increase was not observed. The underlying mechanism for the observed threshold phenomenon is presented in this study, which can be attributed to the thermal diffusion and subsequent explosive boiling after the completion of the interaction between the nanosecond laser pulse and silicon. Based on our delayed Phase explosive model, the ablation depths were calculated for different wavelengths and compared to experimental results. Plasma shielding during laser irradiation was included in the model, which plays a key role to the coupling of laser energy to the irradiated material. © 2008 American Institute of Physics. DOI: 10.1063/1.2978369
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Thermal model of Phase Explosion for high-power laser ablation
High-Power Laser Ablation IV, 2002Co-Authors: Quanming Lu, Richard E RussoAbstract:Although laser ablation of solid materials is finding applications in a growing number of fields, the basic mechanisms underlying laser ablation processes have not been fully understood. One fundamental parameter for high-power laser ablation applications is the ablation depth resulting from the interaction of individual laser pulses. The ablation depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 20 GW/cm 2 . Above this threshold, micron-sized particulates have been observed to eject from the target surface. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of laser irradiation is a possible mechanism to describe the observed dramatic increase of the ablation depth. Calculations based on this delayed Phase Explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation plays an important role on this threshold phenomenon.
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delayed Phase Explosion during high power nanosecond laser ablation of silicon
Applied Physics Letters, 2002Co-Authors: Quanming Lu, Richard E RussoAbstract:An important parameter for high-irradiance laser ablation is the ablation crater depth, resulting from the interaction of individual laser pulses on a targeted surface. The crater depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 2×1010 W/cm2, above which, large (micron-sized) particulates were observed to eject from the target. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of the laser pulse is a possible mechanism for the observed dramatic increase of the ablation depth. Calculations based on this delayed Phase Explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation has a profound effect on this threshold phenomenon.
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existence of Phase Explosion during laser ablation and its effects on inductively coupled plasma mass spectroscopy
Analytical Chemistry, 2001Co-Authors: Oleg V Borisov, Richard E RussoAbstract:A sudden increase in crater depth was observed during high irradiance (>1010 W/cm2) laser ablation of silicon, and it is attributed to the phenomenon of Phase Explosion. The threshold irradiance for Phase Explosion showed a dependence on two laser parameters: laser beam spot size and wavelength. For a larger beam size and longer incident wavelength, a higher laser irradiance was required to generate Phase Explosion. The rapid increase of crater depth above the Phase Explosion threshold irradiance correlated with a significant increase in the ICPMS signal intensity. The ratio of crater volume to ICPMS intensity, which represents entrainment efficiency, remained the lowest at laser irradiances slightly above the Phase Explosion threshold. However, this ratio increased at irradiances well above the threshold (>1011 W/cm2). Chemical analysis using laser ablation at irradiance above 1011 W/cm2 provides increased sensitivity via improved entrainment and transport efficiency and increased ablation rate.