激光驱动气库材料可用于实现准等熵压缩，为了预估样品靶前表面的峰值压力及分析样品靶前表面压力随时间变化曲线，建立了一个简化的理论模型用于描述这一物理过程。激光入射在气库材料上产生冲击波，冲击波到达气库材料背表面卸载使其成为等离子体，进而在真空中自由膨胀。在膨胀的过程中，等离子体密度、温度不断降低，并堆积在样品前端使样品表面的温度、压力缓慢上升，实现准等熵压缩。将气库材料近似为多方气体，对其进行分层处理，求解得到每一层等离子体自由膨胀的解析解，进而编写程序计算多层等离子体堆积在样品前端压力随时间变化曲线。与实验上获得样品自由面粒子速度后用背积分方法获得的样品前端压力随时间变化曲线进行对比，较为吻合，表明这种模型可以用于预估样品前端压力。

Laser-driven reservoir can be used to generate quasi-isentropic compression. In this paper, a method is proposed to estimate the pressure at the front of the sample. When laser-driven shock wave relaxes after reaching the rear surface of reservoir, the generated plasma expands in the vacuum, and ultimately piles up at the front of the sample with low pressure and temperature, and in time period longer than that without vacuum. Assuming the unloading reservoir as a poly-tropic gas, and dividing it into several layers, the analytic self-similar solution is obtained for every layer to describe the velocity, pressure, and density of the plasma expansion into the vacuum. With the solutions, a computation code is given to calculate the time dependent pressure. Compared with the experimental back integrated results, the simplified model is reasonable to estimate pressure at the front of the sample.