A ytterbium-doped large mode area photonic crystal fiber (LMA PCF) femtosecond laser dual-stage amplifier is experimentally studied.Single polarization LMA PCFs are used in the oscillator and pre-amplifier,while a 7-core LMA PCF is used in the main-amplifier.The seven cores are arranged in array type with a mode field area up to 5000 μm2 which effectively suppress the nonlinearity in the fiber.In addition,the heat and stress induced beam distortions are reduced because the cores are discrete distributed.At low pump power,the output features a complex beam profile resulting from a superposition of several supermodes.Flat in-phase supermode and Gaussian-shaped far-field distribution are realized under high pump power.Average power of 24 W laser pulses at a repetition rate of 1 MHz are obtained.The pulses duration can be compressed to 110 fs with peak power up to 150 MW.