相对论自诱导透明啁啾辅助离子加速
Chirp assisted ion acceleration via relativistic self induced transparency
摘要：
研究了啁啾激光脉冲对亚波长靶传输和伴随离子加速的影响。在啁啾激光脉冲中，脉冲频率关于其基频具有时间变化，这体现为临界密度（$n_c$）的时间依赖性。在这项工作中，我们使用了啁啾模型，这是超越线性近似。对于负（正）啁啾脉冲，脉冲的高（低）频率分量与目标相互作用，最初是低（高）频率分量。的阈值等离子体密度的脉冲的传输被发现是较高的负啁啾激光脉冲相比，无啁啾或正啁啾脉冲。对于更高密度（$6n_c$）的负啁啾脉冲的增强的传输导致靶电子的非常有效的加热，在靶后面产生非常稳定和持久的纵向静电场。电子的空隙导致靶离子在任一方向上的膨胀，从而导致宽的能谱。我们在主层后面引入了非常薄的低密度（$< n_c$）次级层。然后发现来自次级层的离子在由初级层在与负啁啾脉冲相互作用时产生的静电场的影响下被加速为单能束。在最佳条件下，质子的最大能量为10 fs（强度fwhm）的$\sim 100$ MeV;峰值强度为$\sim 8.5\times 10^{20}$ W/cm $^2$的圆偏振高斯负啁啾激光脉冲。
英文摘要：
We study the effect of the chirped laser pulse on the transmission and associated ion acceleration by the sub-wavelength target. In the chirped laser pulses, the pulse frequency has a temporal variation about its fundamental frequency, which manifests to the temporal dependence of the critical density ($n_c$). In this work we used a chirp model which is beyond the linear approximation. For negatively (positively) chirped pulses, the high (low) frequency component of the pulse interacts with the target initially followed by the low (high) frequency component. The threshold plasma density for the transmission of the pulse is found to be higher for the negatively chirped laser pulses as compared to the unchirped or positively chirped pulses. The enhanced transmission of the negatively chirped pulses for higher densities ($6n_c$) results in very efficient heating of the target electrons, creating a very stable and persistent longitudinal electrostatic field behind the target. The void of the electrons results in expansion of the target ions in either direction, resulting in the broad energy spectrum. We have introduced a very thin, low density ($< n_c$) secondary layer behind the primary layer. The ions from the secondary layer are then found to be accelerated as a mono-energetic bunch under the influence of the electrostatic field created by the primary layer upon interaction by the negatively chirped pulse. Under the optimum conditions, the maximum energy of the protons are found to be $\sim 100$ MeV for 10 fs (intensity fwhm); Circularly Polarized; Gaussian; negatively chirped laser pulse with peak intensity $\sim 8.5\times 10^{20}$ W/cm$^2$.
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