Hädrich, S.S.HädrichShestaev, E.E.ShestaevTschernajew, M.M.TschernajewStutzki, F.F.StutzkiWalther, N.N.WaltherJust, F.F.JustKienel, M.M.KienelSeres, I.I.SeresJójárt, P.P.JójártBengery, Z.Z.BengeryGilicze, B.B.GiliczeVárallyay, Z.Z.VárallyayBörzsönyi, Á.Á.BörzsönyiMüller, M.M.MüllerGrebing, ChristianChristianGrebingKlenke, A.A.KlenkeHoff, D.D.HoffPaulus, G.G.G.G.PaulusEidam, T.T.EidamLimpert, JensJensLimpert2022-09-302022-09-302022https://publica.fraunhofer.de/handle/publica/42717910.1364/OL.4509912-s2.0-8512664888035290358Two-stage multipass-cell compression of a fiber-chirpedpulse amplifier system to the few-cycle regime is presented. The output delivers a sub-2-cycle (5.8 fs), 107W average power, 1.07 mJ pulses at 100 kHz centered at 1030nm with excellent spatial beam quality (M2=1.1, Strehl ratio S=0.98), pointing stability (2.3 μrad), and superior longterm average power stability of 0.1% STD over more than 8 hours. This is combined with a carrier-envelope phase stability of 360 mrad in the frequency range from 10 Hz to 50 kHz, i.e., measured on a single-shot basis. This unique system will serve as an HR1 laser for the Extreme Light InfrastructureAttosecond Light Pulse Source research facility to enable high repetition rate isolated attosecond pulse generation.enjournal article