Laser-induced plasma formation in Xe, Ar, N_2, and O_2 at the first four Nd:YAG harmonics

Davis, Jon P.; Smith, Allan L.; Giranda, C.; Squicciarini, M.

doi:10.1364/ao.30.004358

Cited by 51 publications

(26 citation statements)

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“…When a lens focuses the laser beam, the distribution of irradiance in the focal spot is determined by the mode structure in the laser oscillator, by the effect of amplifiers and apertures in the system, and by the parameters of the lens. Single-element lenses were used in most of the previous experiments 12,14,20,[22][23][24][25][26] for focusing high-power laser beams and significant spherical aberration was often present, though it may be minimized by a suitable choice of curvatures. The presence of aberrations may lead to erroneous values of optical breakdown threshold even when the measured spot size is used for the determination.…”

Section: Resultsmentioning

confidence: 99%

Energy Absorption and Propagation in Laser-Created Sparks

et al. 2004

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The energy absorption and laser propagation characteristics of air and argon sparks at one atmosphere have been investigated. To create the sparks, 532 nm pulses from a frequency doubled Qswitched Nd : YAG laser are used. We employed 2 ns gated fast photography for studying the time evolution of the kernel at early times. Optical emission spectroscopy is used to infer temperature and density of the sparks. Significant energy absorption by the plasma is observed just above the breakdown threshold. The energy absorption and propagation in the spark indicated that argon plasma is more absorptive than air plasma. The absorption of the spark increases with laser energy, and at higher energies absorption saturation is observed. A spiky behavior is observed in the transmitted temporal profiles of lasers at higher energies and this is explained as due to the formation of a self-regulating regime.

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Section: Resultsmentioning

confidence: 99%

Energy Absorption and Propagation in Laser-Created Sparks

et al. 2004

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“…The first and second derivatives shown in equation (1) are solved numerically using a finite difference technique. The linear part of the equation is solved applying step-by-step integration method.…”

Section: Methods Of Calculationmentioning

confidence: 99%

“…During the eighties of the last century, it was possible to obtain laser source that operates at different wavelengths covering a range from IR up to VUV of the electromagnetic radiation. This source has been used by different research groups [1,[4][5][6][7][8] to carry out measurements on the variation of the threshold intensity with the laser wavelength in the breakdown of atomic and molecular gases. This study is devoted to analyzing the dependence of the threshold intensity on both laser wavelength and gas pressure.…”

Section: Introductionmentioning

confidence: 99%

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Role of Loss Mechanisms in the Breakdown of Argon Irradiated with IR Laser Radiation

Nassef

Gamal

2018

Arab Journal of Nuclear Sciences and Applications

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Threshold intensity measurements of the breakdown of argon are numerically analyzed. The breakdown is induced by a Nd: YAG laser radiation at wavelength of 1064 nm and pulse duration of 8.5 ns.The investigation considered argon over pressure range extended from 25 torr-760 torr.The measured threshold intensity corresponding to this pressure range is found to vary between 5.4xl0 11 W/cm 2 and 1.1xl0 11 W/cm 2. These are the experimental conditions given by Davis et al. [1]. The analysis considers an electron cascade model given previously by Evans and Gamal (1980) [2] and modified by Gamal and Shafik [3]. The model solves the time dependent energy equation numerically in addition to a set of equations describing the rate of change of the formed excited states population. For realistic results, most of the physical processes that might take place during the interaction of laser radiation with the gas are included in the modified model. The calculated threshold intensity showed reasonable agreement with the measured values over the tested pressure range. The obtained values of the electron energy distribution function as well as the time variation of the electrons density for selected gas pressures, revealed that photo-ionization of the formed excited states plays a minor role for electron generation and plasma formation over the studied gas pressure range. Collisional ionization is the main mechanism responsible for the breakdown process. The loss process, due to electron diffusion, is found to have significant contribution only at pressures ≤ 40 torr. On the other hand, the recombination process is acting in a pronounced manner for the higher pressure regime.

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“…The f#~55 launch configuration resulted in the lowest beam exit divergence (Ө exit ~ 0.014) corresponding to M 2 of ~15 at the fiber exit. With pulse energy of ~35 mJ for this condition, the focal intensity was as high as ~ 470 GW/cm 2 well above the break down threshold intensity [5,13,21,22],. The occasional (2%) misfires are thought to be due to varying multimode spatial profile (hot spots) in the exit beam [14,15].…”

Section: Practical Hollow Fiber Configurations (2-m Fibers)mentioning

confidence: 89%

Fundamental Studies of Ignition Process in Large Natural Gas Engines Using Laser Spark Ignition

Yalin¹,

Willson²

2008

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Past research has shown that laser ignition provides a potential means to reduce emissions and improve engine efficiency of gas-fired engines to meet longer-term DOE ARES (Advanced Reciprocating Engine Systems) targets. Despite the potential advantages of laser ignition, the technology is not seeing practical or commercial use. A major impediment in this regard has been the "open-path" beam delivery used in much of the past research. This mode of delivery is not considered industrially practical owing to safety factors, as well as susceptibility to vibrations, thermal effects etc. The overall goal of our project has been to develop technologies and approaches for practical laser ignition systems. To this end, we are pursuing fiber optically coupled laser ignition system and multiplexing methods for multiple cylinder engine operation. This report summarizes our progress in this regard. A partial summary of our progress includes: development of a figure of merit to guide fiber selection, identification of hollow-core fibers as a potential means of fiber delivery, demonstration of bench-top sparking through hollow-core fibers, single-cylinder engine operation with fiber delivered laser ignition, demonstration of bench-top multiplexing, dual-cylinder engine operation via multiplexed fiber delivered laser ignition, and sparking with fiber lasers. To the best of our knowledge, each of these accomplishments was a first. 3 List of Tables Executive SummaryPast research has shown that laser ignition is a potential means to reduce emissions and improve engine efficiency of gas-fired engines to meet longer-term DOE ARES (Advanced Reciprocating Engine Systems) targets. From a fundamental point of view, the benefits of laser ignition (over conventional ignition) are due to: 1) the freedom to locate the laser spark in the middle of the combustion volume away from electrodes and walls which act as heat sinks; and 2) the higher power density of laser sparks, which lead to faster early flame growth and more robust early flame kernels. Additionally, laser ignition avoids limitations of conventional spark including erosion and dielectric breakdown, both of which become increasingly problematic as engine motored pressures increase. Past laser ignition efforts have generally employed "open-path" beam delivery, which is not considered industrially practical owing to safety factors, as well as susceptibility to vibrations, thermal effects etc. The overall goal of our project has been to develop technologies and approaches for practical laser ignition systems. (The project goal is inconsistent with the title of the project; however, very early in the life of the project the goals and milestones were re-scoped by DOE and the research team.) To enable practical systems we have pursued fiber optically coupled laser ignition systems and multiplexing methods for multiplecylinder engine operation. The approaches are selected in order to be compact, rugged, reliable and with the potential for low-cost. For multi-cylinder operation w...

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Laser-induced plasma formation in Xe, Ar, N_2, and O_2 at the first four Nd:YAG harmonics

Cited by 51 publications

References 18 publications

Energy Absorption and Propagation in Laser-Created Sparks

Energy Absorption and Propagation in Laser-Created Sparks

Role of Loss Mechanisms in the Breakdown of Argon Irradiated with IR Laser Radiation

Fundamental Studies of Ignition Process in Large Natural Gas Engines Using Laser Spark Ignition

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