长脉冲激光打靶的直接驱动方式效率较高，但对激光强度变化非常敏感。利用测量自由面速度历史的方法对激光直接驱动准等熵压缩实验技术进行了分析，为改进激光直接驱动的准等熵压缩实验技术提供技术基础。介绍了国内在神光III原型装置上首次开展的激光直接驱动自由面准等熵压缩实验。对实验靶型、激光波形、典型实验结果以及实验中的关键技术进行了分析。在激光能量为1000 J的实验中，使用成像型速度干涉仪获得了较为理想的准等熵压缩条纹图。实验发现，自由面速度达到11.3 km/s 时，自由面反射的探针光信号消失。通过对比Multi-1D 软件的理论模拟数据与实验处理的结果，发现由于Al自由面缺少约束，这类实验会造成波系复杂化的问题，但是对主冲击的研究还是有意义的。对某些特殊材料，在很难找到阻抗匹配窗口的条件下，利用激光直接驱动方式研究材料高压响应特性提供了另一条可实施的技术途径。

Laser indirect-drive has the potential to get ultra-high pressure which is very useful for shock physics. The isentropic compression experiment with long pulse in laser direct-drive is very sensitive to the laser intensity variation. The important technique for isentropic compression experiment with long pulse in laser direct-drive has been introduced with the diagnosis of free surface velocity. The improvement way can be obtained from the experimental data. The target, experimental data and the important technique can be analyzed. The full velocity history of free surface can be achieved after design and control the laser pulse with the comparison of experiment data under 1000 J laser energy. The signal of free surface disappears when the free surface velocity reaches 11.3 km/s. After comparing the simulation data with Multi-1D program and experimental result, the complex of shock wave system in Al sample has been shown because there is no confinement on the free surface. However, this technology is useful to study the main shock wave in the sample. When the sample with transparent window is difficult to manufacture, these experimental data show the technology for the further development of isentropic compression experiment with long pulse in laser direct-drive.