Anharmonic resonance absorption of short laser pulses in clusters: A molecular dynamics simulation study

Mahalik, S. S.; Kundu, M.

doi:10.1063/1.4972085

Cited by 8 publications

(32 citation statements)

References 65 publications

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“…Laser vector potential is defined in the dipole approximation as A(z,t) = A(t) exp(−i2πz/λ ) ≈ A(t) = (E 0 /ω) sin 2 (ωt/2n) cos(ωt) for 0 < t < nT ; where n is the number of laser period T , τ = nT is the total pulse duration and E 0 = 8πI 0 /c is the field strength for the peak intensity I 0 . Defining E l (t) = −dA/dt, one finds [32,33]…”

Section: Wavelength Shift Of Resonance Absorption Using Rigid Sphmentioning

confidence: 99%

“…Beyond λ ≈ 240 nm, argon cluster becomes significantly over-dense as seen from Fig.3(d) (and also from its inset) where (λ /λ M ) 2 > 2. In this regime of λ > 240 nm, only AHR plays the dominant role [25,33] as a collisionless process behind the absorption, outer ionization and charging of the argon cluster and the approximate effective field…”

Section: B Dynamical Resonance Shift and Unification Of Resonancesmentioning

confidence: 99%

“…The cluster charging, absorption and outer ionization for λ > 300 nm are poorer than their respective values at the near-the-LR under-dense wavelength of λ ≈ 140 nm. In this over-dense regime of λ > 300 nm, clearly LR does not play any role but cluster charging, absorption and outer ionization still happen [Figs.4(b)-4(d)] due to the dominant AHR process [25,26,33].…”

Section: Time Domain Analysis Of the Resonance Shiftmentioning

confidence: 99%

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Dynamical resonance shift and unification of resonances in short-pulse laser-cluster interaction

Mahalik

Kundu

2018

Phys. Rev. A

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Pronounced maximum absorption of laser light irradiating a rare-gas or metal cluster is widely expected during the linear resonance (LR) when Mie-plasma wavelength λ M of electrons equals the laser wavelength λ . On the contrary, by performing molecular dynamics (MD) simulations of an argon cluster irradiated by short 5-fs (fwhm) laser pulses it is revealed that, for a given laser pulse energy and a cluster, at each peak intensity there exists a λ -shifted from the expected λ M -that corresponds to a unified dynamical LR at which evolution of the cluster happens through very efficient unification of possible resonances in various stages, including (i) the LR in the initial time of plasma creation, (ii) the LR in the Coulomb expanding phase in the later time and (iii) anharmonic resonance in the marginally over-dense regime for a relatively longer pulse duration, leading to maximum laser absorption accompanied by maximum removal of electrons from cluster and also maximum allowed average charge states for the argon cluster. Increasing the laser intensity, the absorption maxima is found to shift to a higher wavelength in the band of λ ≈ (1 − 1.5)λ M than permanently staying at the expected λ M . A naive rigid sphere model also corroborates the wavelength shift of the absorption peak as found in MD and un-equivocally proves that maximum laser absorption in a cluster happens at a shifted λ in the marginally over-dense regime of λ ≈ (1 − 1.5)λ M instead of λ M of LR. Present study may find importance for guiding an optimal condition laser-cluster interaction experiment in the short pulse regime.

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Section: Wavelength Shift Of Resonance Absorption Using Rigid Sphmentioning

confidence: 99%

Section: B Dynamical Resonance Shift and Unification Of Resonancesmentioning

confidence: 99%

Section: Time Domain Analysis Of the Resonance Shiftmentioning

confidence: 99%

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Dynamical resonance shift and unification of resonances in short-pulse laser-cluster interaction

Mahalik

Kundu

2018

Phys. Rev. A

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“…For a given cluster we choose r 0 = r w , which produces accurate Mie-plasma frequency ω M (see Ref. [27]). The modified Coulomb force on i-th particle and the corresponding potential at its location are,…”

Section: A Details Of MD Simulationmentioning

confidence: 99%

Collisionless absorption of short laser pulses in a deuterium cluster: dependence of redshift of resonance absorption peak on laser polarization, intensity and wavelength

Mahalik,

Kundu

2018

Preprint

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We study collisionless absorption of short laser pulses of various intensity, wavelength (λ ) and polarization in a deuterium cluster using molecular dynamics (MD) simulation. For a given laser energy and a pulse duration ≈ 5-fs (fwhm), it is found that maximum laser absorption does not happen at the welknown static Mie-resonance or linear resonance (LR) wavelength of λ M ≈ 263 nm (for deuterium cluster) irrespective of linear polarization (LP) and circular polarization (CP) state of laser. As the laser intensity increases, the absorption peak is gradually redshifted to a higher λ in the marginally over-dense regime of λ≈(1−1.5)λ M from the expected static λ M owing to gradual outer ionization and cluster expansion; and above an intensity the resonance absorption peak disappears (sometimes followed by even a growth of absorption) when outer ionization saturates at 100% for both LP and CP. This disappearance of the resonance absorption peak should not be misinterpreted as the negligible (or no) role of Mie-resonance. In fact, in this marginally over-dense band of λ ≈(1−1.5)λ M , some electrons undergo dynamic Mie-resonance (dynamic LR) and others anharmonic resonance when they are freed. It is also found that before the absorption peak, laser absorption due to LP and CP lasers are almost equally efficient (CP case being inappreciably higher than LP) for all intensities and λ . However, after the absorption peak, at lower intensities, absorption due to LP inappreciably dominates absorption due to CP with increasing λ which gradually reverses at higher intensities. MD results are also supported by a naive rigid sphere model of cluster.

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“…2(a) suggests that laser frequency chirp also plays an important role in the rapidly evolving cluster. The system can be compared to a driven oscillator that is in resonance when the effective frequency of the electron cloud is matched to the laser frequency 33 . Over each cycle of rising intensity, the ionization and electron energies increase.…”

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confidence: 99%

Temporal feedback control of high-intensity laser pulses to optimize ultrafast heating of atomic clusters

Streeter

Dann

Scott

et al. 2018

Applied Physics Letters

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We describe how active feedback routines can be applied at limited repetition rate (5 Hz) to optimize highpower (> 10 TW) laser interactions with clustered gases. Optimization of x-ray production from an argon cluster jet, using a genetic algorithm, approximately doubled the measured energy through temporal modification of the 150 mJ driving laser pulse. This approach achieved an increased radiation yield through exploration of a multi-dimensional parameter space, without requiring detailed a priori knowledge of the complex cluster dynamics. The optimized laser pulses exhibited a slow rising edge to the intensity profile, which enhanced the laser energy coupling into the cluster medium, compared to the optimally compressed FWHM pulse (40 fs). Our work suggests that this technique can be more widely utilized for control of intense pulsed secondary radiation from petawatt-class laser systems.Petawatt lasers are now able to operate with pulse repetition rates of 1 Hz 1 and upcoming facilities using more efficient, lower thermal load diode-pumped solid state technology will increase this to 10 Hz 2 or more. One of the major drivers for the increase in average power of such high peak-power systems is to generate bright laserplasma based secondary sources to provide user beamlines, similar to existing light-source facilities, or energetic particle beams for a range of applications. This move to a higher repetition rate opens the possibility to employ active feedback routines to optimize energy conversion into radiation or particle beams. Due to highly complex non-linear dynamics in intense laser-plasma interactions, the optimal laser pulse properties for generation of the secondary source can not easily be predicted, as this is both computationally demanding and requires a complete understanding of all the key physical processes involved. Also, optimization is a many-dimensional problem and so cannot readily be performed by scanning individual parameters.Sophisticated feedback techniques, usually employing kHz repetition rate lasers operating at relatively low peak intensity, are well-established for coherent control of atomic and molecular processes 3 . Programmable elements in the laser system are used to tailor the spatial and temporal profile of the laser pulse at focus to optimize specific output parameters. One method is to use a genetic algorithm (GA) to select the most suitable profiles out of an initially random or pseudo-random set and, over a number of generations, the input parameters are evolved to improve the chosen output property (referred to as the fitness function). The great benefit of this approach is that it can achieve advantageous results without detailed knowledge of the interaction itself, and lead to new and unexpected results.Previous experiments have employed feedback loops to control high harmonic generation 4,5 , cluster dynamics 6-8 and electron beam properties 9 through temporal and spatial pulse shaping. These studies were performed with low energy pulses (< 20 mJ) and, with the excepti...

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Anharmonic resonance absorption of short laser pulses in clusters: A molecular dynamics simulation study

Cited by 8 publications

References 65 publications

Dynamical resonance shift and unification of resonances in short-pulse laser-cluster interaction

Dynamical resonance shift and unification of resonances in short-pulse laser-cluster interaction

Collisionless absorption of short laser pulses in a deuterium cluster: dependence of redshift of resonance absorption peak on laser polarization, intensity and wavelength

Temporal feedback control of high-intensity laser pulses to optimize ultrafast heating of atomic clusters

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