Mechanism and computational model for Lyman-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>-radiation generation by high-intensity-laser four-wave mixing in Kr-Ar gas

Louchev, Oleg A.; Bakule, Pavel; Saito, Norihito; Wada, Satoshi; Yokoyama, Koji; Ishida, K.; Iwasaki, M.

doi:10.1103/physreva.84.033842

Cited by 8 publications

(4 citation statements)

References 44 publications

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“…26 First, MPI Keldysh model 29,30 with the modification 31 gives the following expression for the ionization rates:…”

Section: Photoionization Pathwaysmentioning

confidence: 99%

“…26 The rate of Kr excitation is defined by the cross section for the resonant two-photon absorption (TPA) σ (2) , laser intensity I 1 and Kr density as follows…”

Section: Aip Advances 6 095018 (2016)mentioning

confidence: 99%

“…General approach to the optimization of nonlinear conversion of laser radiation is based on the combined computational modeling of (i) the equations of non-linear frequency conversion and (ii) laser absorption effects inducing photoionization kinetics, heating, change of refractive indexes and dephasing. [25][26][27][28] In this work we consider a reduced model which is limited only by the main mechanisms involved in the onset of discharge enabling us to develop the analytical treatment of laser-gas photoionization kinetics with explicit estimations of the related photoionization thresholds. Firstly, we suggest the analytical approximations for (i) photoionization kinetics by the involved laser harmonics and (ii) threshold input laser intensities corresponding to the onset of full-scale discharge.…”

Section: Introductionmentioning

confidence: 99%

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Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

et al. 2016

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We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.

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“…26 First, MPI Keldysh model 29,30 with the modification 31 gives the following expression for the ionization rates:…”

Section: Photoionization Pathwaysmentioning

confidence: 99%

“…26 The rate of Kr excitation is defined by the cross section for the resonant two-photon absorption (TPA) σ (2) , laser intensity I 1 and Kr density as follows…”

Section: Aip Advances 6 095018 (2016)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

et al. 2016

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“…In addition, e and m refer to the electron charge and mass, respectively. In the expression of E, I indicates the power density of the incident laser, n is the refraction index, ε 0 is the permittivity, and c refers to the speed of light in a vacuum [29] . In the present case, I ¼ 10 12 − 10 13 W∕cm 2 , ω ¼ 1.78 × 10 15 s −1 , so ε osc ¼ 10 −2 − 10 −1 eV, which is lower than the ionization potentials J N ¼ 14.53 eV (nitrogen) and J O ¼ 13.62 eV (oxygen).…”

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confidence: 99%

Theoretical and experimental investigations on the threshold of a laser-induced breakdown of air

et al. 2016

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The threshold of a laser-induced breakdown of air is determined experimentally and theoretically. We find that the ionization of air has two steps: the first step is a multi-photon ionization process, which provides enough "seed electrons" to initiate the next step, and the second one is predominated by cascade ionization, which continues to produce free electrons geometrically until the critical free-electron density for breakdown is reached. So a two-step model based on the Morgan ionization model is established to describe the breakdown process. It is found that the time node dividing the two steps is about 9.8 ns in atmospheric air, and the threshold derived from the two-step model proposed here is more consistent with the experimental results than traditional ionization model.

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Laser-induced breakdown and damage generation by nonlinear frequency conversion in ferroelectric crystals: Experiment and theory

Louchev

Hatano

Saito

et al. 2013

Journal of Applied Physics

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Using our experimental data for ns pulsed second harmonic generation (SHG) by periodically poled stoichiometric LiTaO3 (PPSLT) crystals, we consider in detail the mechanism underlying laser-induced damage in ferroelectric crystals. This mechanism involves generation and heating of free electrons, providing an effective kinetic pathway for electric breakdown and crystal damage in ns pulsed operation via combined two-photon absorption (TPA) and induced pyroelectric field. In particular, a temperature increase in the lattice of ≈1 K induced initially by ns SHG and TPA at the rear of operating PPSLT crystal is found to induce a gradient of spontaneous polarization generating a pyroelectric field of ≈10 kV/cm, accelerating free electrons generated by TPA to an energy of ≈10 eV, followed by impact ionization and crystal damage. Under the damage threshold for ns operation, the impact ionization does not lead to the avalanche-like increase of free electron density, in contrast to the case of shorter ps and fs pulses. However, the total number of collisions by free electrons, ≈1018 cm−3 (generated during the pulse and accelerated to the energy of ≈10 eV), can produce widespread structural defects, which by entrapping electrons dramatically increase linear absorption for both harmonics in subsequent pulses, creating a positive feedback for crystal lattice heating, pyroelectric field and crystal damage. Under pulse repetition, defect generation starting from the rear of the crystal can propagate towards its center and front side producing damage tracks along the laser beam and stopping SHG. Theoretical analysis leads to numerical estimates and analytical approximation for the threshold laser fluence for onset of this damage mechanism, which agree well with our (i) experiments for the input 1064 nm radiation in 6.8 kHz pulsed SHG by PPSLT crystal, (ii) pulsed low frequency 532 nm radiation transmission experiments, and also (iii) with the data published for other nonlinear crystals and operated wavelengths.

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Mechanism and computational model for Lyman-α-radiation generation by high-intensity-laser four-wave mixing in Kr-Ar gas

Cited by 8 publications

References 44 publications

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

Theoretical and experimental investigations on the threshold of a laser-induced breakdown of air

Laser-induced breakdown and damage generation by nonlinear frequency conversion in ferroelectric crystals: Experiment and theory

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