Ultrafast surface plasmon polariton pulses observed with a dual-probe scanning near-field optical microscopy (DSNOM) utilizing plasmon nano-focusing

Dual-probe scanning near-field optical microscopy consisting of ultrafast surface-plasmon polariton nanofocusing for excitation and spectral interferometry for detection is constructed to observe spatiotemporal dynamics of surface-plasmon polariton (SPP) pulses. Nano focusing of SPP excited by femtosecond laser pulses on a gold taper with a tip radius of ~20 nm is deterministically controlled. We achieve spatiotemporal resolution for probing of 100 nm and 10 fs.