Laser-cluster interaction with subcycle pulses

Abstract

The interaction of intense laser light with atomic nanoclusters is studied with a rigid sphere model and three-dimensional particle-in-cell simulations for ultrashort laser pulses of pulse durations τ down to one optical period T and below. In this subcycle regime not all conventional pulse models are applicable and may lead to unphysical absorption of laser energy. For allowed pulse models, we show that for a given laser peak intensity, and cluster, the efficiency of laser absorption increases as τ shortens and reaches a maximum value in the subcycle regime. For deuterium clusters, where inner ionization quickly saturates, the absorbed energy and outer ionization reaches a peak at τ ≈ 0.8T . For argon clusters, however, such a peak disappears, and energy absorption continues even for τ < 0.8T due to additional inner ionization.

Anomalous collisional absorption of laser pulses in underdense plasma at low temperature

“…This information can be 043102-5 used to find absorption of laser light in an underdense plasma slab. In this case, the fractional absorption of light (at a normal incidence) can be written as [1,2] « = 1 -h/I\nc = 1 -e x p ( -2/qL), (10) where /jnc./t are the incident and the transmitted intensity of light, Kj = (n/nc)Vei/Vg, vg = c*Jl -n/nc is the group velocity of light, and L is the thickness of the plasma slab. The relation a % 2(n/nc)ve\/v% holds when k-, is very small, and it shows that a should vary similarly to vci with respect to Te and Io for a fixed density of the plasma and laser frequency.…”

“…There are a plethora o f collisionless m echanism s, e.g., linear resonance [1 -5 ], anharm onic resonance [6][7][8][9][10][11], Brunei heating [3,4,12], etc., w hich happen only by m eeting specific conditions betw een laser and plasm a param eters. However, collisional absorption [1 -4 ,1 3 -2 0 ] through electron-ion collision (inverse brem sstrahlung) occurs alm ost all the tim e in the subrelativistic laser field.…”

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

“…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]…”

“…In this regime, an electron may pass through anharmonic resonance (AHR) when its dynamical frequency Ω[r(t)] in the anharmonic potential gradually decreases and finally meets the driving ω [25,26]. The role of AHR as a dominant collisionless process in laser cluster interaction is established by theory [27][28][29], particle-in-cell (PIC) simulations [25,26,[30][31][32] and recently by molecular dynamics (MD) simulation [33]. AHR also finds its place for laser absorption in over-dense structured targets [34,35].…”

Influence of excitation and deexcitation processes on the dynamics of laser-excited argon clusters

“…A quantum -classical hybrid description com bining classical MD with a M onte C arlo schem e to " thomas .bornath @ u ni -rostock. de include quantum ionization rates was used in [28], For larger clusters, either M D calculations using a hierarchical tree code [19] or particle-in-cell (PIC) sim ulations [29][30][31] (including the m icroscopic PIC m ethod M icPIC [32,33]) are appropriate. Q uite another method to theoretically investigate the laser-cluster interaction in the case o f larger clusters is hydrodynam ic m odeling [5,34,35] w hich is based on the assum ption that the laser-excited cluster is transform ed into a small, dense plasma.…”