Near-field probing of nanoscale nonlinear optical processes

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.