In fast ignition laser fusion, a high-intensity picosecond laser heats a compressed dense core to achieve ignition. It is theoretically expected that the energy coupling efficiency from the heating laser to the compressed core becomes higher as the wavelength of the heating laser is shorter. This prediction is ready to be experimentally demonstrated using second harmonic generation at Institute of Laser Engineering (ILE), Osaka University. Fundamental and converted second harmonic waves irradiate a target simultaneously in the experiment because crystals for wavelength conversion is installed after a final optical system. In addition, the polarization of the second harmonic wave becomes perpendicular to the original fundamental wave after the wavelength conversion. These features make laser-plasma-interactions complicated. Therefore, three-dimensional particle-in-cell simulations have been conducted to investigate effects of conversion to short wavelength and mixed-beam irradiation with different wavelengths. Simulation results show that the temperature of the generated fast electrons decreases for second harmonic conversion compared to the case of pure fundamental wave and the laser propagates deeper as the wavelength conversion efficiency becomes high. In the case of mixed-beam irradiation, it is found that the second harmonic wave drills the plasma and guides the fundamental wave to the deep region, where pure fundamental wave cannot reach.

在快速点火激光聚变中，高强度皮秒激光器加热压缩的致密芯以实现点火。从理论上讲，随着加热激光器的波长越短，从加热激光器到压缩芯的能量耦合效率越高。大阪大学激光工程学院（ILE）使用二次谐波可以通过实验证明这一预测。基本的和转换的二次谐波在实验中同时照射目标，因为在最终光学系统之后安装了用于波长转换的晶体。另外，在波长转换之后，第二谐波的偏振变得垂直于原始基波。这些特征使激光等离子体相互作用变得复杂。因此，进行了三维粒子模拟，以研究转换为短波长和不同波长的混合束辐照的影响。仿真结果表明，与纯基波的情况相比，二次谐波转换时生成的快速电子的温度降低，并且随着波长转换效率的提高，激光传播更深。在混合光束辐照的情况下，发现二次谐波会在等离子体上钻孔，并将基波引导至无法到达纯基波的深处。仿真结果表明，与纯基波的情况相比，二次谐波转换时生成的快速电子的温度降低，并且随着波长转换效率的提高，激光传播更深。在混合光束辐照的情况下，发现二次谐波会在等离子体上钻孔，并将基波引导至无法到达纯基波的深处。仿真结果表明，与纯基波的情况相比，二次谐波转换时生成的快速电子的温度降低，并且随着波长转换效率的提高，激光传播更深。在混合光束辐照的情况下，发现二次谐波会在等离子体上钻孔，并将基波引导至无法到达纯基波的深处。