The average mixed cluster sizes in different mixing proportions of Ar-CH4 mixed cluster and Ar-H2 mixed cluster in supersonic gas jet are studied by Rayleigh scattering method. It is found that Ar-CH4 mixed cluster could form easily when the mixed Ar and CH4 gas are used in gas jet, and the maximum cluster size is achieved when the content of Ar is 50%. The maximum cluster size of Ar-CH4 mixed cluster is larger than that of either Ar cluster or CH4 cluster. Being different from pure hydrogen cluster which only forms at liquid nitrogen temperature, Ar-H2 mixed cluster can form at room temperature. So this is the first time we have obtained hydrogen cluster at room temperature. Ar-H2 mixed cluster starts to form at H2 content value higher than 40% and it reaches maximum size when the content of H2 is 60%. Hydrogen (deuterium) mixed clusters introduce heavier Ar element on the basis of hydrogen (deuterium) clusters. It will further accelerate the deuterium ions to higher energy in deuterium cluster laser fusion experiments, so we can obtain higher neutron yield and fusion efficiency.

The influence of static vacuum on the cluster size and density of the supersonic gas jet is studied by Raleigh scattering method. It is found that in a range from 3×10-4 Pa to 9.9×104 Pa, the static vacuum has very little influence on the cluster size and desnity. The self-limiting effect which was found for hydrogen cluster at liquid nitrogen temperature is also found for argon cluster at positions far from the nozzle, and it is found to play an important role in the cluster generation and transporation. The result is very valuable for the construction of the desktop neutron source based on laser fusion method, since the pumps and device to supply the vacuum can be reduced and simplified.

Laser plasma interaction (LPI) is an important content in laser plasma related research, and it is one of the key issues related to the success or failure of inertial confinement fusion ignition, and has received extensive attention. In order to suppress the relevant LPI process as much as possible, the major laboratories around the world have developed a variety of beam smoothing methods through decades of research. However, the current understanding and suppression of LPI are still far from enough, and further in-depth studies are still needed. Generally, the research of LPI is based on nanosecond laser driving, and focuses mainly on the effects of the related LPI process caused by nanosecond lasers. However, the LPI processes, such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), etc., occur and develop on a time scale of picoseconds.The comprehensive effect can be studied only on a longer scale of nanosecond. For highly nonlinear LPI processes, the comprehensive effect may be difficult to reflect the real physical laws. The emergence of the picosecond laser has made it possible to study the LPI process in more detail and on a more appropriate time scale. The present research tries to gain an understanding of LPI from a more refined perspective. The experimental research of picosecond laser driving LPI is carried out on the Shenguang-Ⅱ upgrade and picosecond laser facilities. First, a nanosecond laser is used to irradiate a target to generate a large-scale plasma, and a few nanoseconds later, the picosecond laser is injected as an interaction beam to drive the LPI scattering such as SBS and SRS. The spectral signal of backscatter light is measured experimentally by using the method of diffuse reflector. From the research results it is found that the backward signals of the band near the laser wavelength contain, in addition to the true backward SBS component, a large number of interference signals introduced by picosecond laser and nanosecond laser. The interference signal introduced by nanosecond laser can be eliminated by using specific measures, but the interference signal introduced by picosecond laser cannot be eliminated experimentally, which will affect the estimation of the true share of the backward SBS. The comprehensive results show that under different experimental conditions, the backward scatter energy of SBS may be less than half that of the total recorded signals. This result is helpful in further understanding and re-recognizing previous relevant experimental data.