Abstract
We study the nonlinear optical properties of lithium niobate (LiNbO(3)) nanowires (NWs) fabricated by a top-down ion beam enhanced etching method. First, we demonstrate generation and propagation of the second-harmonic (SH) light in LiNbO(3) NWs of typical rectangular cross-sections of 400 x 600 nm(2) and length from 10 to 50 μm. Then, we show local fluorescent excitation of 4',6-diamidino-2-phenylindole (DAPI) dye with the propagated SH signal in standard concentrations as for biological applications. By measuring the detected average power of the propagated fundamental harmonic (FH) and the SH signal at the output of the NWs, we directly prove the dominating role of the SH signal over possible two-photon excitation processes with the FH in the DAPI dye. We estimate that 63 ± 6 pW of the propagated SH average power is required for detectable dye excitation. Finally, we model the waveguiding of the SH light to determine the smallest NW cross-section (around 40x60 nm(2)) which is potentially able to excite fluorescence with a FH intensity below the cell damage threshold.
Highlights
Owing to their specific shape, nanowires (NW) are invaluable building blocks for various nanodevices and important components for future applications [1,2,3]
By measuring the detected average power of the propagated fundamental harmonic (FH) and the SH signal at the output of the NWs, we directly prove the dominating role of the SH signal over possible twophoton excitation processes with the FH in the DAPI dye
We detect the portions of the total propagated FH and SH signals that are scattered towards the camera at the NW output facet
Summary
Owing to their specific shape, nanowires (NW) are invaluable building blocks for various nanodevices and important components for future applications [1,2,3]. A very interesting approach has been suggested which uses NWs in biological studies for performing localized imaging inside cells [6]. For this purpose, a NW has to be inserted into a cell which contains fluorescent material. Laser light is coupled into the NW and excites fluorescent material either with evanescent waves along the NW [7] or with the delivered light at the NW’s opposite side [8] Both of these demonstrated applications use linear optical excitations with visible light and still suffer from the illumination of the surrounding tissue
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