We present experimental evidence of the generation of few-cycle propagating surface plasmon polariton (SPP) wavepackets. Ultrashort plasmonic pulses were generated by few-cycle laser pulses of 5.5 fs to 6.5 fs duration on a thin silver film of 50 nm thickness coated on the face of a right-angle prism to enable Kretschmann-type SPP coupling. SPP pulses were characterized by an autocorrelation-type measurement based on fourth order, nonlinear electron photoemission induced by the SPP field. The evaluation of the measured ultrashort, fringe-resolved autocorrelation curve of the SPP wavepacket (Fig. 1a) resulted in a retrieved SPP pulse length of 6.5 fs, as evidenced by the reconstructed curve in Fig. 1b. This first demonstration of the generation of few-cycle propagating SPP wavepackets on a metal surface has important applications in ultrafast plasmonics.
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