Department of Electronics and Electrical Engineering, Keio University , 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan.
Nano Lett. 2018 Feb 14;18(2):1366-1372. doi: 10.1021/acs.nanolett.7b05078. Epub 2018 Jan 31.
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.
超快表面等离激元（SPP）在飞秒激光脉冲下在等离子体金属锥形尖端上的纳米聚焦使背景自由的局域激发超越了衍射极限。我们演示了在 440nm 和 800nm 处同时对超快 SPP 脉冲进行纳米聚焦，这些脉冲与在铝（Al）锥形尖端上制造的公共衍射光栅结构耦合，半径约为 35nm。我们实现了选择性相干反斯托克斯拉曼散射（CARS）显微镜，其中包括 800nm（ω）SPP 泵浦脉冲，该脉冲通过光谱聚焦实现了选择性振动激发，以及 440nm（2ω）SPP 探测脉冲。与单层石墨烯的 ω-CARS 相比，这种新型 2ω-CARS 的拉曼强度在 G 带增加了 3.96 倍，在 2D 带增加了 4.00 倍。2ω-CARS 成像方法应用于在 D、G 和 2D 带对多壁碳纳米管进行成像。这种双波长纳米聚焦将在尖端开辟新的纳米级微光谱学和光学激发，如和频混合、双光子激发。
