Simulation And Optimization Of Aperture Optical Probe With A Metal Tip By FDTD

Scanning near-field optical microscope(SNOM) has improved the resolution of conventional optical microscope beyond the diffraction limit.SNOM is applied in near-field optical storage,near-field optical lithography,semiconductor materials and bio-physics research.Optical probe is the key element of SNOM,which determines the resolution of the instrument.The main focus of this thesis is the design and optimization of optical probe.The finite-difference time-domain method(FDTD) is employed to investigate the near-field distribution of the light spot of aperture pyramid-type optical probe with a metal tip. The factors that have some influence on the optical field distribution such as the length,radius and position departed from aperture of the tip are investigated.The mechanism of electromagnetic wave transmitting from the aperture to metal tip by the way of plasmon is discussed.Our calculation results are consistent with the results obtained by Taminiau with different method.How and what the reason that Pohl,etc.have obtained the first images with high resolution in the 20-25nm range between 1984 and 1986 are analyzed.The imaging mechanism of their experiment system is discussed.Numerical simulation has demonstrated that the imaging mechanism of Pohl's experiment system may belong to a scattering-type near-field optical microscope(S-SNOM) rather than an aperture scanning near-field optical microscope(A-SNOM).The L-shaped and V-shaped apertures in a thick metallic screen are optimized by FDTD in this thesis.The influences of aperture's geometry and incident light's polarization state on the near-field optical distribution are studied.The calculation results reveal that both of the light intensity peak of the two kinds of apertures can be enhanced about 100 times more than that of the normal square aperture with the same opening area.It is found that V-shaped aperture can provide a spot size roughly 10-15nm smaller in both the x and y directions than the L-shaped aperture with a comparable light intensity peak until the distance reaches 60nm.Finally,the near-field distribution of the L-shaped and V-shaped apertures with single metal tip is investigated.The components of the electric field are also analyzed.The calculation results reveal that the metal tip near the aperture can further improve the confinement and intensity of the optical field.