We applied a two laser extraordinary Raman spectroscopy technique in a double nanohole optical tweezers setup to excite and detect the vibrational modes of 20 nm polystyrene beads. We measured the quadrupolar accordion mode frequency to be 47.85 GHz and the spherical breathing mode frequency to be 68.72 GHz which are very close to their predicted values. According to our measurements there is a optimum power to excite the vibrational modes and to get sharp peaks in beat frequency spectrum, simultaneously. Improving the resolution of our present Raman spectroscopy system provides a way to more accurately detect changes in resonance frequency, characterize DNA unzipping, protein-DNA interactions, and classify mutant proteins.
Nonlinear optics provides the functionality of wavelength conversion and switching that allows for photonic signal processing and bioimaging. A major obstacle for extreme photonic integration is the requirement to use ultrafast pulsed lasers or to work above the diffraction limit to activate nonlinear optical processes. Here we show that plasmonic enhancement and two dimensional materials provide a promising pathway to extreme photonic integration with nonlinear functionality in nanoscale while using diode lasers.
Here we use optical trapping to isolate single Yb/Er-doped upconversion nanocrystals in plasmonic double nanohole apertures and show that the geometry of the aperture can be tuned to give high emission rate en- hancement. The double nanohole apertures show additional enhancement over the rectangular apertures that were previously demonstrated by our group, producing enough enhancement to observe emission at 400 nm and 1550 nm with 980 nm excitation—not seen in our group’s previous work with rectangular apertures. A facile method for tuning the geometry of double nanohole apertures by adjusting the plasma etching time in the colloidal lithography fabrication process is discussed. We find that a double nanohole with a cusp separation of 32 nm yields the greatest emission enhancement with multiple plasmonic resonances which enhance both the excitation and emission wavelengths. The emission enhancement for the DNH with 32 nm cusp separation was found to be a factor of 54, 44, and 31 greater than the rectangular apertures used in our group’s previous work, for wavelengths of 650 nm, 550 nm, and 400 nm. This result shows that double nanohole apertures can be tuned for emission enhancement as required by specific applications.
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