Optics and Spectroscopy

Transcription

1 Introduction to Optics and Spectroscopy beyond the diffraction limit Chi Chen 陳祺 Research Center for Applied Science, Academia Sinica 2015Apr09 1

2 Light and Optics 2

3 Light as Wave Application 3

4 Electromagnetic Spectrum 4

5 Diffraction Limit Abbe diffraction limit --- by Ernst Abbe, 1873 ϴ d = λ 2n sin θ n d = λ 2N. A. (Numerical Aperture) 5

6 High N.A. Objectives Application d = λ = 532nm 2N.A. 3 ~ 180nm n is usually around for immersion oils, so θ 90 6

7 Resolution Limits Application 7

8 Methods to go beyond the diffraction limit - 1 Near Field Optics 8

9 Far Field Optics Far-Field (Diffraction Limited) ~ 200 nm d = 2N.A. 9

10 Near Field Optics SNOM: Scanning Nearfield Optical Microscopy. Aperture SNOM: Clear aperture for light transmission. 10

11 Aperture SNOM Typical aperture size: nm. 11

12 Aperture SNOM Piezoelectric signal Typical aperture size: nm. 12

13 Apertureless SNOM Metallic tip ~ 300 nm Aperture SNOM Apertureless SNOM (Scattering SNOM) (Tip enhanced SNOM) Resolution: > nm Resolution: < nm 13

14 How Near is Near Field? Evanescent wave 1 Intensity decay I z I 0 e z / d I 0 /I z n 1 =1.52, n 2 =1.33 Incident 70 d / 4 n 2 sin 2 n Z (nm)

15 Typical SPM Working Range Cantilever AFM Tuning fork AFM STM nm nm nm

16 Confine Photon into Nanoscale Localized Surface Plasmon - Collective oscillation of free electrons on a nanoparticle. light Introduction 2 Tip enhancement

17 Surface Enhancement light LSP results in enhancement of EM field

18 Surface Enhancement light LSP results in enhancement of EM field

19 Surface Enhancement light A particle at the apex gives enhancement of EM field

20 Tip Enhancement light STM/AFM Tip LSP results in enhancement of EM field

21 Tip Enhancement light molecule STM/AFM Tip LSP results in enhancement of EM field. Similar to surface enhanced Raman scattering (SERS) Provides location dependent tip enhanced Raman spectrum. 21

22 Tip Enhancement STM/AFM Tip light nm AFM tip 5 µm molecule STM tip 500nm 22

23 Tip Enhanced Raman Imaging Near field Raman (tip enhanced Raman). Optical resolution < 20 nm. CNT / AFM CNT / TERS 200 nm A. Hartschuh et al., Phys. Rev. Lett. 90, (2003) 23

24 STM TERS Imaging of CNT 40 x30 px Simultaneous STM and Raman imaging. TERS 1nm/pixel

25 1.7 nm Optical Resolution C. Chen, N. Hayazawa, and S. Kawata, Nature Comm. 5, 3312 (2014)

26 1.7 nm Optical Resolution World best spatial resolution in optics, spectroscopy, and chemical analysis in the ambient condition. C. Chen, N. Hayazawa, and S. Kawata, Nature Comm. 5, 3312 (2014)

27 Near Field Method Scanning Probe Microscope Sharp tips or probes 50nm Ultrahigh spatial resolution ~ 1nm. Various spectroscopic information. 2D mapping for samples on surface. Not yet successful in liquid. 27

28 Near Field Method Scanning Probe Microscope Sharp tips or probes Far Field Method Inverted Microscope High speed imaging CCD 5 µm 50nm Ultrahigh spatial resolution ~ 2nm. Various spectroscopic information. 2D mapping for samples on surface. Not yet successful in liquid. 28

29 Methods to go beyond the diffraction limit - 2 Fear Field Optics 29

30 Far Field Super Resolution Airy disk (point spread function) From a single emitter. (Fluorescence protein or dye) Localize the center of PSF. 30

31 Far Field Super Resolution Airy disk (point spread function) From a single emitter. (Fluorescence protein or dye) Localize the center of PSF. Resolution > 20nm due to molecular diffusion and motions 31

32 Localization - PALM E. Betzig et al., 313, 1642 (2006). 32

33 Localization - STORM M. Bates, B. Huang, G. T. Dempsey, X. Zhuang, Science 317, (2007) 33

34 Near Field Method Scanning Probe Microscope Sharp tips or probes Far Field Method Inverted Microscope High speed imaging CCD 5 µm 50nm Ultrahigh spatial resolution ~ 1nm. Various spectroscopic information. 2D mapping for samples on surface. Not yet successful in liquid. Good for biological samples. Pseudo 3D imaging. Resolution > 20 nm. Need huge amount of computation. Fluorescence label needed. 34

35 Absorption and Emission 35

36 Interaction of Electron and E Field m Application M Electrons response to the E field. Electrons Polarizability Susceptibility Dielectric function Refraction index. Resonance will result in absorption and dispersion 36

37 Re-emission and Resonance m Application M Nonresonance 1-10 fs re-emission (scattering) Resonance : absorption ns re-emission (photoluminescence) 37

38 Resonance 38

39 Energy Diagram 39

40 Fluorescence 40

41 Stokes Shift The Stokes shift is the gap between the maximum of the absorption band and the maximum of the spectrum. Loss of vibrational energy (relaxation) in the excited state is dissipated as heat by collision with solvent. 41

42 Vibronic Transition 42

43 Mirror Image of Abs and Fl Absorption spectrum vibrational levels of the electronically excited state Emission spectrum vibrational levels of the electronic ground state Fluorescence spectrum is mirror image of absorption spectrum 43

44 Example of Fluorescent Dyes fluorescein ethidium bromide bound to DNA. 44

45 Fluorescence Lifetime The lifetime ( ) of the lowest excited singlet state. The average time the molecule spends in the excited state prior to return to the ground state. Generally, fluorescence lifetimes are around 10 nsec. 45

46 Fluorescence Lifetime Time correlated single photon counting. 46

47 Quantum Yield Quantum Yield f number of photons emitted number of photons absorbed 47

48 Quantum Yield 48

49 Quantum Yield and Molecular Structure 49

50 Raman Scattering 50

51 Scattering of Light True solution (No scattering) Colloidal solution (Scattering of light)

52 Scattering of Light Remitted photon without energy resonance. Colloidal solution (Scattering of light)

53 Scattering of Light Remitted photon without energy resonance % of scattered photon keeps the same energy as incident photon. Rayleigh scattering.

54 Scattering of Light 99.99% of scattered photon keeps the same energy as incident photon. Rayleigh scattering. < 0.01 % of scattered photon exchanges energy with the media molecules. Raman scattering.

55 Discovery of Raman Scattering C.V. Raman (India) Discovery of the inelastic scattering of photon Nobel prize in physics.

56 Raman and Rayleigh Scattering

57 Raman and Rayleigh Scattering

58 Resonance Raman Stronger Raman signal due to electronic resonance. May accompany with fluorescence.

59 Raman and Molecular Vibration

60 Raman and Molecular Vibration

61 Gymnastics of Water Molecule Rotation Bending Stretching

62 Raman Spectroscopy for Molecular Fignerprint

63 Raman Spectroscopy for Molecular Fignerprint

64 Vibration Spectroscopy: Raman v. s. IR

65 Experimental Setup line filter Notch filter 45 dichloric beamsplitter

66 Extremely Expensive Filters Laser line cleanup filter Notch filter line filter Notch filter 45 dichloric beamsplitter 45 dichloric beamsplitter

67 Raman for Bio Molecules DNA line filter Notch filter 45 dichloric beamsplitter

68 Raman for Bio Molecules Label-free imaging for different cellular components

69 SERS Surface Enhanced Raman Scattering SERS is a surface sensitive technique. Huge enhancement on rough metal surfaces. The enhancement factor can be as much as High sensitivity possibly for single molecule detection.

70 SERS SERS is a surface sensitive technique. Huge enhancement on rough metal surfaces. The enhancement factor can be as much as High sensitivity possibly for single molecule detection.