Picosecond Ionization Dynamics in Femtosecond Filaments at High Pressures

Gao, Xiaohui; Patwardhan, Gauri; Schrauth, Samuel E.; Zhu, Daiwei; Gaeta, Alexander L.

doi:10.1364/cleo_si.2015.sm3n.2

Cited by 3 publications

(5 citation statements)

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“…As a consequence of this sequential coupling, avalanche ionization does not instantaneously follow the intensity, leading to memory or transient effects. As a related example exhibiting such memory effects, for a laser-produced high temperature plasma in air it has been shown both theoretically and experimentally that the plasma density can continue to increase well after the pulse has passed due to the high energy electrons in the tail of the Maxwell distribution that have enough energy for impact ionization of neutral atoms [27][28][29]. The distinction in the present case is that the mean kinetic energy of the freed electrons already is enough to produce impact ionization both during and after the pulse.…”

Section: Overview Of the Standard Modelmentioning

confidence: 99%

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Memory effects in the long-wave infrared avalanche ionization of gases: a review of recent progress

et al. 2019

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There are currently intense efforts being directed towards extending the range and energy of long distance nonlinear pulse propagation in the atmosphere by moving to longer infrared wavelengths, with the purpose of mitigating the effects of turbulence. In addition, picosecond and longer pulse durations are being used to increase the pulse energy. While both of these tacks promise improvements in applications, such as remote sensing and directed energy, they open up fundamental issues regarding the standard model used to calculate the nonlinear optical properties of dilute gases. Amongst these issues is that for longer wavelengths and longer pulse durations, exponential growth of the laser-generated electron density, the so-called avalanche ionization, can limit the propagation range via nonlinear absorption and plasma defocusing. It is therefore important for the continued development of the field to assess the theory and role of avalanche ionization in gases for longer wavelengths. Here, after an overview of the standard model, we present a microscopically motivated approach for the analysis of avalanche ionization in gases that extends beyond the standard model and we contend is key for deepening our understanding of long distance propagation at long infrared wavelengths. Our new approach involves the mean electron kinetic energy, the plasma temperature, and the free electron density as dynamic variables. The rate of avalanche ionization is shown to depend on the full time history of the pulsed excitation, as opposed to the standard model in which the rate is proportional to the instantaneous intensity. Furthermore, the new approach has the added benefit that it is no more computationally intensive than the standard one. The resulting memory effects and some of their measurable physical consequences are demonstrated for the example of long-wavelength infrared avalanche ionization and long distance high-intensity pulse propagation in air. Our hope is that this report in progress will stimulate further discussion that will elucidate the physics and simulation of avalanche ionization at long infrared wavelengths and advance the field. arXiv:1810.07345v2 [physics.optics]

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Section: Overview Of the Standard Modelmentioning

confidence: 99%

“…This is correct and it is well known that impact excitation of excited atomic states can also occur and reduce the amount of ionization that occurs. To address this issue will require an extension of the current model to go beyond the freed electron density and allow for the excited state populations [29].…”

Section: Recurring Issuesmentioning

confidence: 99%

Memory effects in the long-wave infrared avalanche ionization of gases: a review of recent progress

et al. 2019

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“…Studies of photoionization by strong optical fields have led to a number of interesting developments in physics, ranging from fundamental studies of ionization and subsequent plasma evolution [1][2][3] to applications such as high harmonic generation (HHG) [1] and the formation of plasma channels that can be used in particle acceleration and for the generation of coherent X-rays [4]. While these initial studies focused on low-density gases, recent research has explored the full nonlinear polarization of gases at atmospheric and higher pressures [5], as well as more exotic effects such as Kramers-Henneberger quasibound states [6], and avalanche ionisation by collisions of excited atoms in the absence of a laser pulse [7][8][9]. Understanding the dynamics of ionised gases at high pressures is also of great importance for HHG in the water window, a spectral region where phase-matching generally requires helium pressures of several atmospheres [10,11].…”

Section: Introductionmentioning

confidence: 99%

Pump-Probe Study of Plasma Dynamics in Gas-Filled Photonic Crystal Fiber Using Counterpropagating Solitons

et al. 2019

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We present a pump-probe technique for monitoring ultrafast polarizability changes. In particular, we use it to measure the plasma density created at the temporal focus of a self-compressing higher-order pump soliton in gas-filled hollow-core photonic crystal fiber. This is done by monitoring the wavelength of the dispersive wave emission from a counter-propagating probe soliton. By varying the relative delay between pump and probe, the plasma density distribution along the fiber can be mapped out. Compared to the recently introduced interferometric side-probing for monitoring the plasma density, our new technique is relatively immune to instabilities caused by air turbulence and mechanical vibration. The results of two experiments on argon-and krypton-filled fiber are presented, and compared to numerical simulations. The technique provides an important new tool for probing photoionization in many different gases and gas mixtures as well as ultrafast changes in dispersion in many other contexts.

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“…Such high-pressure (and multiply ionized) noble gases were used to achieve efficient ultrahigh-harmonic generation, in which case the combination of linear response of electron gas and nonlinear response of ions was shown to engineer phase matching with the driving UV laser pulse. 5,23,24 Most recently, timeresolved transverse interferometry and shadowgraphy was used to trace evolution of the electron density in the filament wake in a highpressure argon gas (60 bar) on picosecond time scale, 1 where an approximately 3-fold increase in the electron density was observed, saturating at about 30 picoseconds after the filamenting laser pulse.…”

mentioning

confidence: 99%

“…In this Communication, we investigate theoretically the evolution of a dense gas during interaction with an intense, ultrashort laser pulse. Similar to recent experimental work, 1 we assume an argon gas at a pressure of 60 atm. This gas interacts with a laser pulse at 800 nm, a duration of 70 fs (FWHM), and a focal-volume intensity in the range 0.5-1.0 × 10 14 W/cm 2 .…”

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confidence: 99%

Intrapulse impact processes in dense-gas femtosecond laser filamentation

et al. 2018

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The processes of energy gain and redistribution in a dense gas subject to an intense ultrashort laser pulse are investigated theoretically for the case of high-pressure argon. The electrons released via strong-field ionization and driven by oscillating laser field collide with neutral neighbor atoms, thus effecting the energy gain in the emerging electron gas via a short-range inverse Bremsstrahlung interaction. These collisions also cause excitation and impact ionization of the atoms thus reducing the electron-gas energy. A kinetic model of these competing processes is developed which predicts the prevalence of excited atoms over ionized atoms by the end of the laser pulse. The creation of a significant number of excited atoms during the pulse in highpressure gases is consistent with the delayed ionization dynamics in the pulse wake, recently discovered by Gao et al 1 . This energy redistribution mechanism offers an approach to manage effectively the excitation vs. ionization patterns in dense gases interacting with intense laser pulses and thus opens new avenues for diagnostics and control in these settings. In the wake of a filamenting laser pulse, the system of energetic free electrons, ions, and

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Picosecond Ionization Dynamics in Femtosecond Filaments at High Pressures

Cited by 3 publications

References 41 publications

Memory effects in the long-wave infrared avalanche ionization of gases: a review of recent progress

Memory effects in the long-wave infrared avalanche ionization of gases: a review of recent progress

Pump-Probe Study of Plasma Dynamics in Gas-Filled Photonic Crystal Fiber Using Counterpropagating Solitons

Intrapulse impact processes in dense-gas femtosecond laser filamentation

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