Selective Coherent Anti-Stokes Raman Scattering Microscopy Employing Dual-Wavelength Nanofocused Ultrafast Plasmon Pulses

Ultrafast surface plasmon polariton (SPP) nanofocusing on a plasmonic metal tapered tip with femtosecond laser pulses enables background-free localized excitation beyond the diffraction limit. We demonstrate simultaneous nanofocusing of ultrafast SPP pulses at 440 and 800 nm, which were coupled with a common diffraction grating structure fabricated on an aluminum (Al) tapered tip, to the tip apex with a radius of ∼35 nm. We achieved selective coherent anti-Stokes Raman scattering (CARS) microscopy that combined an 800 nm (ω) SPP pump pulse, which achieves selective vibrational excitation by spectral focusing, and a 440 nm (2ω) SPP probe pulse. Raman intensity of this novel 2ω-CARS increased by a factor of 3.96 at the G-band and 4.00 at the 2D-band compared with that with ω-CARS for the monolayer graphene. The 2ω-CARS imaging method was applied for imaging a multiwalled carbon nanotube at the D-, G-, and 2D-bands. This dual-wavelength nanofocusing will open up new nanoscale microspectroscopy and optical excitation at the tip apex, such as sum frequency mixing, two-photon excitation

Media 1: High-speed multispectral videography with a periscope array in a spectral shaper

Originally published in Optics Letters on 15 December 2014 (ol-39-24-6942

Media 2: Design for sequentially timed all-optical mapping photography with optimum temporal performance

Originally published in Optics Letters on 15 February 2015 (ol-40-4-633

Media 1: Design for sequentially timed all-optical mapping photography with optimum temporal performance

Originally published in Optics Letters on 15 February 2015 (ol-40-4-633