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Nanophotonics in Microscopy Lecture 12 – Nanophotonics in Microscopy EECS 598-002 Winter 2006 Nanophotonics and Nano-scale Fabrication P.C.Ku Schedule for the rest of the semester Introduction to light-matter interaction (1/26): How to determine ε(r)? The relationship to basic excitations. Basic excitations and measurement of ε(r). (1/31) Structure dependence of ε(r) overview (2/2) Surface effects (2/7): Surface EM wave Surface polaritons Size dependence Case studies (2/9 – 2/16): Quantum wells, wires, and dots Nanophotonics in microscopy Nanophotonics in plasmonics Dispersion engineering (2/21 – 3/7): Material dispersion Waveguide dispersion (photonic crystals) EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 2 Principles of optical microscopy The information contained in the object/image is carried by the light wave to the detector (e.g. eyes). Information = F(x,y) Æ F(,kkxy ) EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 3 Optical vs electron microscopy Advantages of optical microscopes Photon energy is low (~ eV). Electron energy is high (~10-100 keV) -27 Photon momentum is low (~ 10 kg m/s). Electron momentum is high (~ 10-23 -10-22 kg m/s) Especially good to study optical processes (including nonlinear optical response) in the sample Ultra-short optical pulse is available to study ultra-fast processes Can make the fluorescence work Æ useful for biological imaging Disadvantages of optical microscopes Photon does not have charge. Cannot study the Coulomb interaction in the sample. Photon does not reveal information regarding the chemical composition of the sample (unless we go to the x-ray wavelength). EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 4 Resolution limits of optical microscopes Small features correspond to large (kx, ky) components. In traditional optical microscopes, the detector sees the light in the far fieldk region. 2 2 222 k==++ωµε0 kkkxyz 22 ⇒+<⇒kkxyω nck/2/&,max =πλ n 17.5 15 Resolving power 12.5 k-space real-space 10 = λλ/2( n) ≡ eff /2 7.5 5 = diffraction limit 2.5 −2/π n λ 2/π n λ k& -2 -1 1 2 λ / n EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 5 Finite-size lens In a real system, the cutoff spatial frequency is often limited by the size of the lens which is quantitatively described by a numerical aperture (NA). NA≡ n sinθ k 2π ⇒=⇒=&,max sinθ k NA k &,max λ θ Resolving power Æ λλ/2NA( ) ≡ eff /2 where λeff = λ /NA EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 6 Resolution enhancement Shortening of wavelength: Decrease the wavelength of light source Increase the refractive index (e.g. immersion microscope) Using nonlinear optical effect (e.g. frequency doubling) Increase the detectable spatial frequency Moire grating Near field optics to detect the evanescent waves Ref: S. Kawata, chapter 2, figure 1. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 7 Scanning Near-field Optical Microscope EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 8 Different modes of SNOM Ref: Prasad, chapter 3, figure 7. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 9 Detection of near field intensity modulation The modulation of the near-field intensity can be detected at the far-field region: e.g. Thin slab photon tunneling d = wavelength/4 1 Transmission 0.9 Reflection 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 40 60 80 100 Incident Angle EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 10 Configuration of SNOM Ref: Prasad, chapter 3, figure 8. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 11 Near-field probes (aperture in an opaque screen) (e.g. PSTM) Green: evanescent wave Ref: S. Kawata, chapter 2, figure 6. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 12 Advantages of apertureless probes No cutoff frequency as existing in a metal-coated fiber optics probe Field enhancement due to surface plasmon polaritons The probe size can be made much smaller EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 13 Controlling the probe-sample distance (1) feedback excitation (2) laser laser beam splitter segment ed photodiode cant i l ever The tip-sample distance changes the damping sampl e of the resonance oscillator. Ref: Prasad, chapter 3, figure 9. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 14 Laser trapping for probe Ref: S. Kawata, chapter 8. e.g. 2.5W Nd-YLF traps a gold particle (~ 10-100 nm) with a 100X NA=1.35 objective (oil immersion) EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 15 Examples of SNOM images 1 Single molecule fluorescence detection location Laser detuning Ref: W. E. Moerner, Science 265 (1994) 46. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 16 Examples of SNOM images 2 Single quantum dot Ref: T. Saiki and Y. Narita, Jpn. J. Appl. Phys., 37 (1998) 1638. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 17 Examples of SNOM images 3 Dynamics using pump-probe technique t = 30 ps t = 0 ps Ref: Y. Shen et al., J. Phys. Chem. B 107 (2003) 13551. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 18 Examples of SNOM images 4 Topography 0 14500 0 28000 830,25nm 21000 829,53nm 0 21000 0 14000 SNOM 0 6000 0 Background 0 80000 0 1300 0 0 61000 0 18000 15 microns scan range VCSEL 0 8000 0 120 00 Taken from presentation materials of WITEC. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 19 Examples of SNOM images 5 MFM - Magnetic Force Microscopy 80 microns scan range 20 microns scan range 5 microns scan range PC hard drive Taken from presentation materials of WITEC. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 20 Examples of SNOM images 5 Semiconductor Surface Study Topography SNOM 20% In (a) (b) (c) 24% In (d) (e) (f) InGaN films Jeongyong Kim et al., University of Illinois, see also APL Vol. 80, 6, 989 (2002). 27% In (g) (h) (i) 10 microns scan range Taken from presentation materials of WITEC. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 21 Examples of SNOM images 7 Topography Adhesion 5 microns scan range Bodyguard adhesive tape Taken from presentation materials of WITEC. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 22 Reading S. Kawata, chapter 2. EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 23.
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