Nonlinear nanophotonics is continuously shaped by advances in nanofabrication, creating new nano-objects that come in unconventional architectures. An intriguing class of such nano-objects includes semiconductor nanowires exhibiting high crystallinity, polarization anisotropy, and high optical nonlinearities. Vertically-aligned nanowires provide the best route to device integration due to maximization of the surface-volume ratio and ease of fabrication [1], [2]. To understand and exploit the nonlinear optical effects in such a nanowire, it is crucial that light can be coupled well into it. Previously, we have shown that the second-harmonic generation (SHG) from a single pristine semiconductor nanowire could be driven well by the longitudinal electric fields and can be even used to reliably map the longitudinal electric fields of focused vector beams [3]. However, little is still known about the higher-order harmonic emissions of strongly absorbing materials like GaAs that could occur in the UV regime. It is believed that such high-harmonic emissions are difficult to probe due to wide absorption resonances obscuring the possible richness of nonlinear phenomena in that spectral regime. Also, the generation of UV light that is compatible for any device engineering effort is becoming essential. New approaches to detect and harness these emissions from advanced nano-objects are thus needed. Here, we show the possibility of probing and manipulating the THG from a single vertically-aligned semiconductor nanowire using polarized vector beams.
Third-harmonic generation (THG) microscopy is demonstrated as a powerful technique to visualize undeveloped photopolymerized microstructures within a negative photoresist film. By comparing the THG microscopy images of developed and undeveloped single-photon polymerized structures in a SU-8 film, THG was found to provide sufficient contrast for distinguishing polymerized and unpolymerized regions. This also suggests that the technique can be used as a complementary technique to visualize the effect of photoresist development where microstructure shrinkage could occur. In addition, we applied the technique to visualize a three-photon polymerized microstructure that was fabricated in the same microscopy setup. This demonstrates the potential of the technique for in situ microscopy of photopolymerized microstructures in three dimensions.
We introduce the use of second-harmonic generation microscopy to investigate individual persistent luminescent microparticles that are either embedded in glass or as prepared. Three-dimensional mapping of the second-harmonic generation from monoclinic dysprosium- and europium-doped strontium aluminates, a popular persistent luminescent material, allows us to unambiguously visualize and reveal for the first time the presence of micrometer-sized structured domains from such microparticles. The technique was found to have high potential for studying noninvasively a wide range of individual persistent luminescent entities that are embedded in a variety of glass matrices.
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