Frequency doubled Nd:YAG lasers represent an attractive alternative to other laser tools for many material processing applications, but frequency doubling with pulsed Nd:YAG lasers has been performed until now only with pulses of tens of nanoseconds. In material processing with longer pulses (10-1000 mus), such as encountered in typical 1.06 mum industrial Nd:YAG applications, the laser-material interaction is different and, in particular, higher material ablation rates are performed. Furthermore, the green light material processing permits a better focusability and a higher absorption in most materials. However, frequency doubling with long pulse lasers is much more difficult and less efficient up to now. The main problems are the generation of a fundamental 1.064 mum beam of high quality necessary for the non-linear process, and the low damage threshold of the non linear materials in the long pulse regime. Therefore, a zigzag slab laser, which has a high beam quality and an inherently linear polarisation of the beam, is an ideal candidate for non-linear processes. The optical damage threshold in the non-linear materials is the main limiting parameter. The 140 W instantaneous power obtained for a 200 mus pulse duration in extra-cavity configuration allows us to finely process sheets up to 300 mum thick.
Tobias Kippenberg, Rui Ning Wang, Xinru Ji, Zheru Qiu, Andrea Bancora, Yang Liu, Andrey Voloshin
Philip Johannes Walter Moll, Chunyu Guo, Hao Yang