Growth, saturation, and collapse of laser-driven plasma density gratings

Abstract

Two nonlinear theoretical models are presented to describe the time evolution of a plasma density grating induced by intersecting high power laser beams. The first model is based on the fluid equations, while the second is a kinetic model that adopts the particle mesh method. It is found that both models can describe the plasma density grating formation at different stages, well beyond the linear growth stage. However, the saturation of the plasma density grating, which is attributed to the kinetic effect of "ion wave-breaking", can only be predicted by the second model based on the particle mesh method. Using the second model, we also find that the saturation time of the plasma density grating increases with the plasma density and decreases with the laser intensity. The results from these two nonlinear theoretical models are compared and verified using particle-in-cell simulations.

Depolarization of intense laser beams by dynamic plasma density gratings

“…In addition, we find that the plasma temperature will increase gradually. Correspondingly, the peak density of the PDG will decrease due to the enhanced thermal pressure [ 32 , 33 ] . This may finally set a limitation on the use of dynamic PDGs in hot plasmas.…”

“…To understand the depolarization of laser beams, we first investigate the dynamics of the PDG, which can be well described by the fluid model in the linear stage in 1D cases [ 31 , 32 ] . For simplicity, two driver laser beams in the theoretical analysis are assumed to have constant intensities, and they propagate oppositely along the positive or negative -axis into a homogeneous plasma.…”

“…where is the plasma frequency. After the linear growth stage, however, the saturation, collapse and regrowth of the PDG will take place [ 32 , 33 ] . Further, the formed PDG will be nonuniform, since the driver laser beams always have finite durations and spot sizes in reality.…”

“…It is illustrated that the peak density of the PDG increases gradually to a maximum value in the first development stage. Then the PDG will saturate and collapse due to the ion wave breaking [ 32 , 33 ] . Interestingly, the formation of the PDG will restart again after its collapse.…”

Plasma zone plate for high-power lasers driven by a Laguerre-Gaussian beam

“…The transition from stage II to stage III can be found as the density variation develops from proportional to ∇ 2 f (r) in figure 2(c) to negatively correlated with f (r) in figure 2(d), which is marked by the emergence of the density peak at x = 0, y = 0 at around 2.5ps as shown in figure 2(a). As the density variation in stage III is analytically difficult to resolve, we designed a particle-fluid program [34] to numerically calculate the ion density evolution based on equation (12). A comparison of the ion density in stage III (t = 4ps) between our particle-fluid program and the PIC simulation is presented in figure 2(d).…”