Kholaif, S.S.KholaifJauregui, C.C.JaureguiTu, Y.Y.TuLimpert, JensJensLimpert2022-10-122022-10-122022https://publica.fraunhofer.de/handle/publica/42757210.1117/12.26095152-s2.0-85131222470Several studies have reported mitigation strategies of transverse mode instability. These are usually based either on reducing the strength of the thermally induced refractive index grating (RIG) and/or the modal interference pattern (MIP) along the fiber amplifier or on manipulating the phase shift between the RIG and the MIP. Here we report that a heat load modulation can be achieved by pulsing the seed and/or the pump in bursts, which induces a positive phase shift. In this way, a beam cleaning is achieved, which improves the performance of the amplifier system by allowing for operation with a diffraction-limited beam profile at an average output power significantly higher than the TMI threshold. The heat load modulation technique delivers a stable beam at an average output power higher than 1.5 times the TMI threshold with an instantaneous intra-burst power of around four times higher than the TMI threshold.enamplitude modulationFiber amplifiersheat loadmode instabilitiesthermal effectsconference paper