Thomas, J.J.ThomasHeinrich, M.M.HeinrichBurghoff, J.J.BurghoffNolte, S.S.NolteAncona, A.A.AnconaTünnermann, A.A.Tünnermann2022-03-032022-03-032007https://publica.fraunhofer.de/handle/publica/21388810.1063/1.2799178We report on thermally stable optical waveguides written in periodically poled lithium niobate with a femtosecond laser using a two line approach. Both fundamental and second harmonic light at 1064 and 532 nm are guided with low damping losses. In a 10-mm-long sample a conversion efficiency of 58% was achieved.en620621journal article