Near-field probing of nanoscale nonlinear optical processes

Abstract

We report a study of two nonlinear optical processes at the nanoscale level, using a near-field probe: (i) two-photon-pumped upconversion from ZnS:Mn nanoparticles encapsulated with 2-[{(?) -2-[4 -(ethylsulfonyl) phenyl]- 1-ethenyl} (methyl)anilino]- 1-ethanethiol and (ii) second-harmonic generation (SHG) from N -(4-nitrophenyl)- (L) -prolinol crystallites. The use of highly efficient nonlinear organic chromophores together with special processing on the nanometer scale made it possible to observe and characterize what are believed to be the smallest topographically distinguishable objects reported so far, using nonlinear optical techniques. Issues pertaining to the study of two-photon-excited emission and SHG by use of a near-field probe are discussed.

Two-photon fluorescence scanning near-field microscopy based on a focused evanescent field under total internal reflection

“…To date, either near-field probes that incorporate subwavelength aperture f iber tips with 4 or without metal coating 2,3 or apertureless metallic tips 5 have been employed for two-photon excitation. The use of an uncoated f iber tip with a tip apex of 200 nm has shown a resolution of ϳ175 nm, 2 whereas the use of a metallic tip greatly enhances the field near the tip, producing a resolution of ϳ40 nm with a tip apex of 10 nm.…”

Near‐field second‐harmonic generation from gold nanoellipsoids

“…A further effect is the resonant excitation of the so-called Localized Surface Plasmons (LSPs) [5]; the resonance frequencies of the LSP can be tailored in a broad spectral range according to the material and shape of the nanostructure. Local field enhancements (LFEs) are best observed exploiting nonlinear optical effects, such as Second-Harmonic Generation (SHG) [6][7][8][9][10] or Two-Photon Photo-Luminescence (TPPL) [7,11,12] which depend on the square of the light intensity. In order to observe a significant non-linear response, the samples need to be illuminated by high peak intensities such as those associated with very short laser pulses.…”

Second harmonic generation in the near field and far field: A sensitive tool to probe crystalline homogeneity

“…[2][3][4][5] In the framework of second harmonic generation ͑SHG͒ studies, neither signal nor resolution has been improved since the early articles 2,6 and they are still far from what could have been expected with respect to the recent progress of scanning near-field optical microscopy ͑SNOM͒. [2][3][4][5] In the framework of second harmonic generation ͑SHG͒ studies, neither signal nor resolution has been improved since the early articles 2,6 and they are still far from what could have been expected with respect to the recent progress of scanning near-field optical microscopy ͑SNOM͒.…”