High power femtosecond chirped pulse ampliflcation in large mode area

Abstract We report on high power ampli¯cation offemtosecond pulses in 40- ¹ m core diameter Yb-dopedphotonic bandgap Bragg ¯bers. The robustness to bend-ing and transverse spatial behavior of these ¯bers isanalyzed through simulations. The ¯bers are used inboth stages of a moderately stretched (150 ps) femtosec-ond chirped pulsed ampli¯cation (CPA) system. A com-pressed average power of 6.3 W is obtained using a low-index polymer-coated Bragg ¯ber with excellent beamquality and high e±ciency, in agreement with numeri-cal simulations. The use of an air-clad Bragg ¯ber al-lows us to scale the output power to 47 W at a repeti-tion rate of 35 MHz. This experiment demonstrates thegreat potential of Bragg ¯bers to increase the mode areaand the power of practical bending-tolerant femtosecond¯ber systems.1 IntroductionThe use of ytterbium-doped ¯bers to amplify femtosec-ond pulses is now widely recognized as an alternative so-lution to bulk systems, especially for high-average powersystems [1]. Indeed, for ¯bers a few meters in length, thehigh surface-to-volume ratio induces an excellent ther-mal handling capability, allowing the generation of highaverage power radiation at high repetition rates. More-over, the spectral gain of ytterbium ions in silica glassis wide enough (40 nm) to produce pulses a few hun-dred femtoseconds in duration [2]. Finally, if the ¯ber is