Quasi-isentropic compression technique is very useful for new material, shock wave physics, and earth physics. With shaping pulse laser, the quasi-isentropic compression technique is provided. For the designed experimental condition, the high energy density of shaping lasers can be used to generate shockless loading on the solid material to reach a high compression rate state with low temperature, which cannot be obtained with shock compression and isentropic compression technique. Then a new way to study the material can be provided. In this paper, the isentropic compression experiment with laser direct-drive illumination based on Shen Guang-III prototype laser facility is conducted. The theoretical model, target designing, experimental results, key technique, experimental characteristics and experimental data are analyzed in detail. The compression pressure above 400 GPa on the loading surface is obtained with experimental data and processing program, which is the highest pressure achieved to date. After comparing the apparent particle velocity with the true particle velocity, the dynamic correction curve can be obtained to achieve the real particle velocity, which is more accurate. The improving direction is provided, which will provide the important information. The experimental data and design will give the valuable reference for the study in this field.

Laser indirect-drive has the potential to obtain ultra-high pressure which is very useful for shock physics. The isentropic compression can be obtained with reservoir target in laser indirect-drive experiment. The free surface velocity and interface velocity are the two important parameters in isentropic compression experiment. The efficiency with reservoir target is lower than that in the isentropic compression experiment with long pulse laser direct-drive. However, the isentropic compression experiment with long pulse in laser direct-drive is very sensitive to the laser intensity variation. In this paper, the isentropic compressions with reservoir target with indirect-drive and direct-drive on Shen Guang-Ⅲ prototype laser facility are investigated separately. And the important technique is introduced to provide the reference data in this field. And the isentropic compression with long pulse laser direct-drive is analyzed on Shen Guang-Ⅲ prototype laser facility. The interface velocity on Al/LiF is achieved with three steps. The blank effect is provided and analyzed. These data show that with long pulse in laser direct-drive, a pressure, which has been highest in China up to now, can be obtained. With these experiment data, the feasibility to do the isentropic compression experiment on Shen Guang-Ⅲ prototype laser facility has been approved.

LiF is often used as a window in laser-driven shock experiments, which can transmit and reflect visible probe laser. Researches of LiF transparency almost focus on its optical reflectivity compressed by strong shock, but there is almost no research on its optical transmissivity compressed by weak shock. In order to study the optical transmissivity of LiF, the quasi-isentropic compression experiment is carried out on the ShenGuang-III prototype laser facility, in which the velocity interferometer system for any reflector is used to diagnose the optical reflectivity of the quasi-isentropic compression sample CH/Al/LiF. The experimental results indicate that the velocity interferometer fringes are missing in the late stage of this experiment. The probe laser should penetrate LiF before it hits the rear surface of aluminum and the laser reflected by aluminum should penetrate LiF before it is collected by the velocity interferometer system for any reflector. Therefore, the reflectivity diagnosed by the velocity interferometer system for any reflector is the product of the optical reflectivity of aluminum and the optical transmissivity of LiF under the experimental condition. However, there is no research about the optical transmissivity model of thick LiF compressed by laser-driven shock. In this paper, we develop a transmissivity model for transparent window LiF and simulate the optical reflectivity of sample CH/Al/LiF. Firstly, we simulate the temperature and density of the sample by the code for one-dimensional multigroup radiation hydrodynamics (MULTI-1D). Then, based on the resulting temperature and density, we simulate the optical reflectivity of the sample by using the optical reflectivity model of aluminum and the optical transmissivity model of LiF. Without considering the transparency of LiF, the simulated result indicates that there is no signal missing in the late stage, which is different from the experimental result. By considering the transparency of LiF, the simulated result is in good agreement with the experimental result. The simulated result indicates that the formation of the strong shock, because of the later shock's catching up with the early one, obviously reduces the optical transparency of LiF and finally causes the velocity interferometer fringes to disappear. The simulated result also indicates that the energy gap of LiF calculated from density-functional theory is 1-2 eV. In this experiment, when LiF becomes opaque, its temperature is 1 eV and its pressure is 2-3 Mbar.