Focused on silicon surface in water, superimposed multiple shots of linearly polarized 800-nm, 100-fs, 10-Hz laser pulses at lower fluence than the single-pulse ablation threshold are shown to produce two kinds of periodic nanostructures with almost constant periods of 150 nm and 400 nm. Surface plasmon polaritons excited in the surface layer illustrates well the formation of nanostructures and its dynamic properties observed. Pump and probe measurements of the ultrafast change in surface reflectivity during the interaction have demonstrated that the multiple low-fluence fs pulses are crucial to the nanostructuring through the accumulation of non-thermal bonding structure change and the subsequent nanoscale ablation.
Tip-enhanced
Raman spectroscopy (TERS) is a nano-optical approach
to extract spatially resolved chemical information with nanometer
precision. However, in the case of direct-illumination TERS, which
is often employed in commercial TERS instruments, strong fluorescence
or far-field Raman signals from the illuminated areas may be excited
as a background. They may overwhelm the near-field TERS signal and
dramatically decrease the near-field to far-field signal contrast
of TERS spectra. It is still challenging for TERS to study the surface
of fluorescent materials or a bulk sample that cannot be placed on
an Au/Ag substrate. In this study, we developed an indirect-illumination
TERS probe that allows a laser to be focused on a flat interface of
a thin-film waveguide located far away from the region generating
the TERS signal. Surface plasmon polaritons are generated stably on
the waveguide and eventually accumulated at the tip apex, thereby
producing a spatially and energetically confined hotspot to ensure
stable and high-resolution TERS measurements with a low background.
With this thin-film waveguide probe, TERS spectra with obvious contrast
from a diamond plate can be acquired. Furthermore, the TERS technique
based on this probe exhibits excellent TERS signal stability, a long
lifetime, and good spatial resolution. This technique is expected
to have commercial potential and enable further popularization and
development of TERS technology as a powerful analytical method.
We have developed and characterized a plasmon-excitation scattering-type near-field scanning optical microscope with sharpened single carbon nanotube probe. The developed microscope can optically capture differences in the refractive index of single-nanometer surface structures. Statistical analysis enabled us to estimate the precision of the optical length measurement to 1.8 nm.
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