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We perform modal characterization on an ytterbium-doped large mode area photonic-crystal-fiber (PCF) amplifier using spatial and spectral (S2) resolved imaging and compare results to conventional cutoff methods. We apply numerical simulations and step-index fiber experiments to calibrate our mathematical and experimental routines of our S2 imaging system. We systematically analyze higher-order-mode (HOM) content of a polarizing 40-μm core double-clad PCF amplifier with various launching and coiling configurations. We demonstrate a HOM suppression of more than −24 dB with variance of 2.3 dB. [ABSTRACT FROM AUTHOR]