High efficiency high beam quality third harmonic generation of hundreds femtosecond laser by employing a delay line and LiB3O5 crystals

In this study, efficient third harmonic generation was investigated by employing a delay line and LiB3O5 (LBO) crystals with 600 fs pulse lasers at 1030 nm. We systematically investigated the differences in the frequency conversion of the LBO crystals for second and third harmonic generation with varying beam spots. Specifically, it has been demonstrated that the inclusion of a delay line is necessary to mitigate the group velocity mismatch at hundreds femtosecond laser. The results indicate that the maximum output powers are approximately 16.5 W and 5.6 W at wavelengths of 515 nm and 343 nm, respectively. The corresponding optimal conversion efficiencies are 59.6 % (from 1030 nm to 515 nm) and 20.4 % (from 1030 nm to 343 nm). And the beam quality has improved noticeably at 515 nm (Mx2 = 1.16, My2 = 1.13) and 343 nm (Mx2 = 1.16, My2 = 1.12), in contrast to that at 1030 nm (Mx2 = 1.56, My2 = 1.49). •High efficiency and high beam quality THG by employing LBO crystals is obtained.•The effectiveness of a delay line for THG of hundreds femtosecond laser is demonstrated.•Different focusing lenses on LBO crystals to stimulate SHG and THG are discussed.•The effects of different types of LBO crystals for THG are investigated.