Research On Near-Field Optical Properties And Manipulation Of Low Loss Polaritons

The emerging nanophotonics,a crossing-field between traditional optics and nano-science,aims at manipulating light and studying light-matter interaction on nanoscale,showing great potentials in quantum physics,photo-catalysis,and bio-sensing.Polaritons,coupling photons with coherent oscillating charges,provide an effective platform for the goal in nanophotonics.The scattering-type scanning near-field optical microscopy?s-SNOM?is a versatile optical imaging technique with nanoscale spatial resolution of 10 nm,which can probe and image polaritons in real space.In order to measure the spectroscopic information of polaritons,we have to develop s-SNOM,making the characterization simultaneously have spatial and spectral resolution,which will be quite important for polaritonics.The two representative members in polaritonics are graphene and hexagonal boron nitride.The state-of-the-art graphene plasmonics exhibit high spatial confinement of mid-infrared light and gate-tunability.However,the lifetime of graphene plasmon remains as 100 fs,which is not enough for the practical applications.Another powerful candidate in polaritonics is phonon polaritons in boron nitride,whose lifetime can reach up to picoseconds.Given of un-tunability due to the wide bandgap and the narrow Reststrahlen band(200 cm^-1)in which phonon polaritons exist,it is always important for nanophotonics to search better polaritonic materials and novel methods for their tuning.The dissertation is categorized into three aspects:1.Build home-made Fourier transform infrared nanospectroscopy?nano-FTIR?simultaneously with spatial??10 nm?and spectral(?6.25 cm^-1)resolution.2.The real space imaging of surface plasmons in indium arsenide?In As?nanowires was carried out for the first time by using near-field imaging technique,and the related physical properties were studied in combination with numerical simulation.We find that surface plasmons simultaneously exhibit high confinement and low propagation loss.Besides,the characteristics of surface plasmons include plasmon wavelength,dispersion,confinement factor and damping rate,can be controlled by changing the nanowire diameter and the surrounding substrate.This can provide a new choice for polaritonic materials.3.Because that phase change materials exhibit two phases with different permittivity,we successfully control the propagation and focusing of phonon polaritons in boron nitride by changing local dielectric environment.The results show that we can engineer polaritonic wavefront and sub-wavelength focusing.Reversible change between two phases of phase change material without damaging polaritonic materials can provide a new idea for the manipulation of polaritons.