The Experts below are selected from a list of 2979 Experts worldwide ranked by ideXlab platform
Richard B. Miles - One of the best experts on this subject based on the ideXlab platform.
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laser induced Avalanche Ionization in gases or gas mixtures with resonantly enhanced multiphoton Ionization or femtosecond laser pulse pre Ionization
2012Co-Authors: Mikhail N. Shneider, Richard B. MilesAbstract:The paper discusses the requirements for Avalanche Ionization in gas or gas mixtures initiated by REMPI or femtosecond-laser pre-Ionization. Numerical examples of dependencies on partial composition for Ar:Xe gas mixture with REMPI of argon and subsequent classic Avalanche Ionization of Xe are presented.
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standoff spectroscopy via remote generation of a backward propagating laser beam
2011Co-Authors: P R Hemmer, Richard B. Miles, Pavel Polynkin, T Siebert, Alexei V Sokolov, P Sprangle, Marlan O ScullyAbstract:In an earlier publication we demonstrated that by using pairs of pulses of different colors (e.g., red and blue) it is possible to excite a dilute ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. This approach is a conceptual step toward spectroscopic probing at a distance, also known as standoff spectroscopy. In the present paper, we propose a related but simpler approach on the basis of the backward-directed lasing in optically excited dominant constituents of plain air, N2 and O2. This technique relies on the remote generation of a weakly ionized plasma channel through filamentation of an ultraintense femtosecond laser pulse. Subsequent application of an energetic nanosecond pulse or series of pulses boosts the plasma density in the seed channel via Avalanche Ionization. Depending on the spectral and temporal content of the driving pulses, a transient population inversion is established in either nitrogen- or oxygen-ionized molecules, thus enabling a transient gain for an optical field propagating toward the observer. This technique results in the generation of a strong, coherent, counterpropagating optical probe pulse. Such a probe, combined with a wavelength-tunable laser signal(s) propagating in the forward direction, provides a tool for various remote-sensing applications. The proposed technique can be enhanced by combining it with the gain-swept excitation approach as well as with beam shaping and adaptive optics techniques.
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laser induced Avalanche Ionization in gases or gas mixtures with rempi or femtosecond laser pulse pre Ionization
2010Co-Authors: Mikhail N. Shneider, Richard B. MilesAbstract:Introduction Recently the scenario for control of Ionization process in atmospheric air by dual femtosecond /nanosecond laser pulse was suggested [1]: a laser plasma may be generated by a preionizing fs pulse with a subsequent long CO2 laser pulse for additional Avalanche Ionization and Joule heating. A similar scenario arises in the case of the Resonance Enhanced Multiphoton Ionization (REMPI) -Avalanche hybrid Ionization with a nanosecond laser pulse at intensities much lower than required for breakdown of the bulk gas. That problem was studied for the Ar:Xe mixture, where during the initial portion of the pulse (3+1) REMPI of Ar atoms starts the Ionization, which subsequently continues to grow with an Avalanche in the buffer Xe gas [2].
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Simultaneous resonant enhanced multiphoton Ionization and electron Avalanche Ionization in gas mixtures
2008Co-Authors: Mikhail N. Shneider, Zhili Zhang, Richard B. MilesAbstract:Resonant enhanced multiphoton Ionization (REMPI) and electron Avalanche Ionization (EAI) are measured simultaneously in Ar:Xe mixtures at different partial pressures of mixture components. A simple theory for combined REMPI+EAI in gas mixture is developed. It is shown that the REMPI electrons seed the Avalanche process, and thus the Avalanche process amplifies the REMPI signal. Possible applications are discussed.
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microwave diagnostics of laser induced Avalanche Ionization in air
2006Co-Authors: Zhili Zhang, Mikhail N. Shneider, Richard B. MilesAbstract:This work presents a simplified model of microwave scattering during the Avalanche Ionization stage of laser breakdown and corresponding experimental results of microwave scattering from laser breakdown in room air. The model assumes and measurements confirm that the breakdown regime can be viewed as a point dipole scatterer of the microwave radiation and thus directly related to the time evolving number of electrons. The delay between the laser pulse and the rise of the microwave scattering signal is a direct measure of the Avalanche Ionization process.
Wolfgang Rudolph - One of the best experts on this subject based on the ideXlab platform.
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modeling the effect of native and laser induced states on the dielectric breakdown of wide band gap optical materials by multiple subpicosecond laser pulses
2010Co-Authors: Luke A Emmert, Mark Mero, Wolfgang RudolphAbstract:A model for the multiple-pulse laser-induced breakdown behavior of dielectrics is presented. It is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations involving transitions between band and mid-gap states (native and laser-induced). Using realistic estimations for the trap density and Ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by Avalanche Ionization seeded by multiphoton Ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the CB. The effect of native and laser-induced defects can be distinguished by their saturation behavior. Finally, measurements of the multiple-pulse damage threshold of hafnium oxide films are used to illustrate the application of the model.
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modeling the effect of native and laser induced states on the dielectric breakdown of wide band gap optical materials by multiple subpicosecond laser pulses
2010Co-Authors: Luke A Emmert, Mark Mero, Wolfgang RudolphAbstract:A model for the multiple-pulse laser-induced breakdown behavior of dielectrics is presented. It is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations involving transitions between band and mid-gap states (native and laser-induced). Using realistic estimations for the trap density and Ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by Avalanche Ionization seeded by multiphoton Ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the CB. The effect of native and laser-induced defects can be distinguished by their saturation behavior. Finally, measurements of ...
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scaling laws of femtosecond laser pulse induced breakdown in oxide films
2005Co-Authors: Mark Mero, Detlev Ristau, Wolfgang Rudolph, Kai StarkeAbstract:The scaling of the single-pulse laser threshold fluence for dielectric breakdown with respect to pulse duration and material band gap energy was investigated in the subpicosecond pulse regime using oxide films (${\mathrm{TiO}}_{2}$, ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$, ${\mathrm{HfO}}_{2}$, ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, and ${\mathrm{SiO}}_{2}$). A phenomenological model attributes the pulse duration dependence to the interplay of multiphoton Ionization, impact Ionization, and subpicosecond electron decay out of the conduction band. The observed linear scaling of the breakdown fluence with band gap energy can be explained within the framework of this model by invoking the band gap dependence of the multiphoton absorption coefficient from Keldysh photoIonization theory. The power exponent $\ensuremath{\kappa}$ of the observed dependence of the breakdown threshold fluence ${F}_{\mathit{th}}$ on pulse duration ${\ensuremath{\tau}}_{p}$, ${F}_{\mathit{th}}\ensuremath{\propto}{\ensuremath{\tau}}_{p}^{\ensuremath{\kappa}}$, is independent of the material and is attributed to photoIonization seeded Avalanche Ionization.
Mikhail N. Shneider - One of the best experts on this subject based on the ideXlab platform.
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Coherent microwave scattering from xenon resonance-enhanced multiphoton Ionization-initiated plasma in air
2020Co-Authors: Christopher A. Galea, Mikhail N. Shneider, Mark Gragston, Zhili ZhangAbstract:Here we present the experimental and computational study of resonance-enhanced multiphoton Ionization (REMPI) of xenon and subsequent Avalanche Ionization of air. Xenon was excited from the ground state to the excited 6p state ( 89 162 cm − 1) by two photons at 224.3 nm. The third photon at 224.3 nm subsequently produced Ionization of xenon in air. The seed electrons from the Ionization served as the medium to further absorb the laser pulse for the rotational and vibrational excitation and Avalanche Ionization of O 2 and N 2. Plasma chemistry of O 2 and N 2 in air was included in the model. The results are useful for understanding REMPI-initiated plasma in air and possibly new diagnostics tools based on REMPI-initiated plasma emissions.Here we present the experimental and computational study of resonance-enhanced multiphoton Ionization (REMPI) of xenon and subsequent Avalanche Ionization of air. Xenon was excited from the ground state to the excited 6p state ( 89 162 cm − 1) by two photons at 224.3 nm. The third photon at 224.3 nm subsequently produced Ionization of xenon in air. The seed electrons from the Ionization served as the medium to further absorb the laser pulse for the rotational and vibrational excitation and Avalanche Ionization of O 2 and N 2. Plasma chemistry of O 2 and N 2 in air was included in the model. The results are useful for understanding REMPI-initiated plasma in air and possibly new diagnostics tools based on REMPI-initiated plasma emissions.
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laser induced Avalanche Ionization in gases or gas mixtures with resonantly enhanced multiphoton Ionization or femtosecond laser pulse pre Ionization
2012Co-Authors: Mikhail N. Shneider, Richard B. MilesAbstract:The paper discusses the requirements for Avalanche Ionization in gas or gas mixtures initiated by REMPI or femtosecond-laser pre-Ionization. Numerical examples of dependencies on partial composition for Ar:Xe gas mixture with REMPI of argon and subsequent classic Avalanche Ionization of Xe are presented.
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laser induced Avalanche Ionization in gases or gas mixtures with rempi or femtosecond laser pulse pre Ionization
2010Co-Authors: Mikhail N. Shneider, Richard B. MilesAbstract:Introduction Recently the scenario for control of Ionization process in atmospheric air by dual femtosecond /nanosecond laser pulse was suggested [1]: a laser plasma may be generated by a preionizing fs pulse with a subsequent long CO2 laser pulse for additional Avalanche Ionization and Joule heating. A similar scenario arises in the case of the Resonance Enhanced Multiphoton Ionization (REMPI) -Avalanche hybrid Ionization with a nanosecond laser pulse at intensities much lower than required for breakdown of the bulk gas. That problem was studied for the Ar:Xe mixture, where during the initial portion of the pulse (3+1) REMPI of Ar atoms starts the Ionization, which subsequently continues to grow with an Avalanche in the buffer Xe gas [2].
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Simultaneous resonant enhanced multiphoton Ionization and electron Avalanche Ionization in gas mixtures
2008Co-Authors: Mikhail N. Shneider, Zhili Zhang, Richard B. MilesAbstract:Resonant enhanced multiphoton Ionization (REMPI) and electron Avalanche Ionization (EAI) are measured simultaneously in Ar:Xe mixtures at different partial pressures of mixture components. A simple theory for combined REMPI+EAI in gas mixture is developed. It is shown that the REMPI electrons seed the Avalanche process, and thus the Avalanche process amplifies the REMPI signal. Possible applications are discussed.
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microwave diagnostics of laser induced Avalanche Ionization in air
2006Co-Authors: Zhili Zhang, Mikhail N. Shneider, Richard B. MilesAbstract:This work presents a simplified model of microwave scattering during the Avalanche Ionization stage of laser breakdown and corresponding experimental results of microwave scattering from laser breakdown in room air. The model assumes and measurements confirm that the breakdown regime can be viewed as a point dipole scatterer of the microwave radiation and thus directly related to the time evolving number of electrons. The delay between the laser pulse and the rise of the microwave scattering signal is a direct measure of the Avalanche Ionization process.
Mark Mero - One of the best experts on this subject based on the ideXlab platform.
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modeling the effect of native and laser induced states on the dielectric breakdown of wide band gap optical materials by multiple subpicosecond laser pulses
2010Co-Authors: Luke A Emmert, Mark Mero, Wolfgang RudolphAbstract:A model for the multiple-pulse laser-induced breakdown behavior of dielectrics is presented. It is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations involving transitions between band and mid-gap states (native and laser-induced). Using realistic estimations for the trap density and Ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by Avalanche Ionization seeded by multiphoton Ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the CB. The effect of native and laser-induced defects can be distinguished by their saturation behavior. Finally, measurements of the multiple-pulse damage threshold of hafnium oxide films are used to illustrate the application of the model.
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modeling the effect of native and laser induced states on the dielectric breakdown of wide band gap optical materials by multiple subpicosecond laser pulses
2010Co-Authors: Luke A Emmert, Mark Mero, Wolfgang RudolphAbstract:A model for the multiple-pulse laser-induced breakdown behavior of dielectrics is presented. It is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations involving transitions between band and mid-gap states (native and laser-induced). Using realistic estimations for the trap density and Ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by Avalanche Ionization seeded by multiphoton Ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the CB. The effect of native and laser-induced defects can be distinguished by their saturation behavior. Finally, measurements of ...
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scaling laws of femtosecond laser pulse induced breakdown in oxide films
2005Co-Authors: Mark Mero, Detlev Ristau, Wolfgang Rudolph, Kai StarkeAbstract:The scaling of the single-pulse laser threshold fluence for dielectric breakdown with respect to pulse duration and material band gap energy was investigated in the subpicosecond pulse regime using oxide films (${\mathrm{TiO}}_{2}$, ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$, ${\mathrm{HfO}}_{2}$, ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, and ${\mathrm{SiO}}_{2}$). A phenomenological model attributes the pulse duration dependence to the interplay of multiphoton Ionization, impact Ionization, and subpicosecond electron decay out of the conduction band. The observed linear scaling of the breakdown fluence with band gap energy can be explained within the framework of this model by invoking the band gap dependence of the multiphoton absorption coefficient from Keldysh photoIonization theory. The power exponent $\ensuremath{\kappa}$ of the observed dependence of the breakdown threshold fluence ${F}_{\mathit{th}}$ on pulse duration ${\ensuremath{\tau}}_{p}$, ${F}_{\mathit{th}}\ensuremath{\propto}{\ensuremath{\tau}}_{p}^{\ensuremath{\kappa}}$, is independent of the material and is attributed to photoIonization seeded Avalanche Ionization.
Zhili Zhang - One of the best experts on this subject based on the ideXlab platform.
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Coherent microwave scattering from xenon resonance-enhanced multiphoton Ionization-initiated plasma in air
2020Co-Authors: Christopher A. Galea, Mikhail N. Shneider, Mark Gragston, Zhili ZhangAbstract:Here we present the experimental and computational study of resonance-enhanced multiphoton Ionization (REMPI) of xenon and subsequent Avalanche Ionization of air. Xenon was excited from the ground state to the excited 6p state ( 89 162 cm − 1) by two photons at 224.3 nm. The third photon at 224.3 nm subsequently produced Ionization of xenon in air. The seed electrons from the Ionization served as the medium to further absorb the laser pulse for the rotational and vibrational excitation and Avalanche Ionization of O 2 and N 2. Plasma chemistry of O 2 and N 2 in air was included in the model. The results are useful for understanding REMPI-initiated plasma in air and possibly new diagnostics tools based on REMPI-initiated plasma emissions.Here we present the experimental and computational study of resonance-enhanced multiphoton Ionization (REMPI) of xenon and subsequent Avalanche Ionization of air. Xenon was excited from the ground state to the excited 6p state ( 89 162 cm − 1) by two photons at 224.3 nm. The third photon at 224.3 nm subsequently produced Ionization of xenon in air. The seed electrons from the Ionization served as the medium to further absorb the laser pulse for the rotational and vibrational excitation and Avalanche Ionization of O 2 and N 2. Plasma chemistry of O 2 and N 2 in air was included in the model. The results are useful for understanding REMPI-initiated plasma in air and possibly new diagnostics tools based on REMPI-initiated plasma emissions.
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resonant and Avalanche Ionization amplification of laser induced plasma in air
2014Co-Authors: Zhili Zhang, Naibo Jiang, Sukesh Roy, James R GordAbstract:Amplification of laser-induced plasma in air is demonstrated utilizing resonant laser Ionization and Avalanche Ionization. Molecular oxygen in air is ionized by a low-energy laser pulse employing (2 + 1) resonance-enhanced multi-photon Ionization (REMPI) to generate seed electrons. Subsequent Avalanche Ionization of molecular oxygen and nitrogen significantly amplifies the laser-induced plasma. In this plasma-amplification effect, three-body attachments to molecular oxygen dominate the electron-generation and -loss processes, while either nitrogen or argon acts as the third body with low electron affinity. Contour maps of the electron density within the plasma obtained in O2/N2 and O2/Ar gas mixtures are provided to show relative degrees of plasma amplification with respect to gas pressure and to verify that the seed electrons generated by O2 2 + 1 REMPI are selectively amplified by Avalanche Ionization of molecular nitrogen in a relatively low-pressure condition (≤100 Torr). Such plasma amplification occurring in air could be useful in aerospace applications at high altitude.
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Simultaneous resonant enhanced multiphoton Ionization and electron Avalanche Ionization in gas mixtures
2008Co-Authors: Mikhail N. Shneider, Zhili Zhang, Richard B. MilesAbstract:Resonant enhanced multiphoton Ionization (REMPI) and electron Avalanche Ionization (EAI) are measured simultaneously in Ar:Xe mixtures at different partial pressures of mixture components. A simple theory for combined REMPI+EAI in gas mixture is developed. It is shown that the REMPI electrons seed the Avalanche process, and thus the Avalanche process amplifies the REMPI signal. Possible applications are discussed.
-
microwave diagnostics of laser induced Avalanche Ionization in air
2006Co-Authors: Zhili Zhang, Mikhail N. Shneider, Richard B. MilesAbstract:This work presents a simplified model of microwave scattering during the Avalanche Ionization stage of laser breakdown and corresponding experimental results of microwave scattering from laser breakdown in room air. The model assumes and measurements confirm that the breakdown regime can be viewed as a point dipole scatterer of the microwave radiation and thus directly related to the time evolving number of electrons. The delay between the laser pulse and the rise of the microwave scattering signal is a direct measure of the Avalanche Ionization process.