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.

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As a typical plasma-based optical element that can sustain ultra-high light intensity, plasma density grating driven by intense laser pulses have been extensively studied for wide applications. Here, we show that the plasma density grating driven by two intersecting driver laser pulses is not only nonuniform in space but also varies over time. Consequently, the probe laser pulse that passes through such a dynamic plasma density grating will be depolarized, i.e., its polarization becomes spatially and temporally variable. More importantly, the laser depolarization may spontaneously take place for crossed laser beams if their polarization angles are arranged properly. The laser depolarization by a dynamic plasma density grating may find the application in mitigating parametric instabilities in laser-driven inertial confinement fusion.

BackgroundAnchorage is one of the most important treatments for severe temporomandibular joint disorder (TMD). Anchoring nails have shown great success in clinical trials; however, they can break under pressure and are difficult to remove. In this study, we aimed to evaluate an improved anchoring nail and its mechanical stability.MethodsThe experiment consisted of two parts: a tensile test and finite element analysis (FEA). First, traditional and improved anchoring nails were implanted into the condylar cortical bone and their tensile strength was measured using a tension meter. Second, a three-dimensional finite element model of the condyles with implants was established and FEA was performed with forces from three different directions.ResultsThe FEA results showed that the total force of the traditional and improved anchoring nails is 48.2 N and 200 N, respectively. The mean (±s.d.) maximum tensile strength of the traditional anchoring nail with a 3–0 suture was 27.53 ± 5.47 N. For the improved anchoring nail with a 3–0 suture it was 25.89 ± 2.64 N and with a 2–0 suture it was above 50 N. The tensile strengths of the traditional and improved anchoring nails with a 3–0 suture was significantly different (P = 0.033–< 0.05). Furthermore, the difference between the traditional anchoring nail with a 3–0 suture and the improved anchoring nail with a 2–0 suture was also significantly different (P = 0.000–< 0.01).ConclusionThe improved anchoring nail, especially when combined with a 2–0 suture, showed better resistance ability compared with the traditional anchoring nail.