Frequency tripling of convergent beam employing crystals tiling in large-aperture high-energy laser facilities

•In inertial confinement fusion (ICF), ultraviolet laser damage of fused silica lens is an important limiting factor for load capability of the laser driver. To solve this problem, we proposed a new third harmonic generation (THG) configuration that the frequency tripling crystal is placed on downstream of the achromatic focusing lens and THG occurs in the beam convergence path. In the new configuration, the focusing lens will be avoided to be irradiated by ultraviolet laser and its damage threshold will significantly increase. Furthermore, the material of focusing lens can be changed to K9 glass.•For meeting the phase matching condition with large convergence angle, LBO crystals are employed as the frequency tripling crystals. Limited by the acceptance angle, a crystal tiling scheme is proposed and designed optimally. By employing this crystal tiling scheme, the growth size limitation of LBO crystal can also be broken through.•We carried out a principle experiment on this new configuration by using a laser with smaller beam aperture, much lower energy and smaller LBO crystals tiling. The experimental results correspond well with the theoretical analysis and demonstrate the feasibility of this new configuration.

In inertial confinement fusion, ultraviolet laser damage of the fused silica lens is an important limiting factor for load capability of the laser driver. To solve this problem, a new configuration of frequency tripling is proposed in this paper. The frequency tripling crystal is placed on downstream of the focusing lens, thus sum frequency generation of fundamental frequency light and doubling frequency light occurs in the beam convergence path. The focusing lens is only irradiated by fundamental light and doubling frequency lights. Thus, its damage threshold will increase. LiB3O5 (LBO) crystals are employed as frequency tripling crystals for its larger acceptance angle and higher damage threshold than KDP/DKDP crystals'. With the limitation of acceptance angle and crystal growth size are taken into account, the tiling scheme of LBO crystals is proposed and designed optimally to adopt to the total convergence angle of 36.0 mrad. Theoretical results indicate that 3 LBO crystals titling with different cutting angles in θ direction can meet the phase matching condition. Compared with frequency tripling of parallel beam using one LBO crystal, 83.8% (93.1% with 5 LBO crystals tiling) of the frequency tripling conversion efficiency can be obtained employing this new configuration. The results of a principle experiment also support this scheme. By employing this new design, not only the load capacity of a laser driver will be significantly improved, but also the fused silica lens can be changed to K9 glass lens which has the mature technology and low cost.