1. New Modalities and Opportunities with Optical Spectroscopy and Microscopy Jung Y. Huang 黃中垚 Department of Photonics, Chiao Tung University Hsinchu, Taiwan http://www.jyhuang.idv.twhttp://www.jyhuang.idv.tw July 6, 2007 Optical spectroscopy discloses the electronic structure associated to a material, while microscopy reveals its real-space configuration. This talk presents an overview on modern optical spectroscopy and microscopy to elicit the ideas useful for the development of photonic science. Sum-frequency vibrational spectroscopy and multi-dimensional FTIR are selected as the illustrating examples to reveal the characteristics and unique opportunity to be bringing out. For optical microscopy, emphasis is focused on the possibility and principles that allow optical microscopy to be employed to probe into the nano world with light.

2.  Current scientific research throughout the natural sciences aims at the exploration of the collectivity of structures with dimensions between 1 and 100nm ( 建構奈米組件 ).  There is a strong demand for technologies offering access to these dimensions, for structuring ( 製造 ), manipulating ( 操控 ), or measuring ( 量測 ) at high resolution.

3. SPATIAL RESOLUTION VS. CHEMICAL INFORMATION

4. Rough estimates of the typical timescales associated to the energies involved in molecular systems

5. Real-Space Configuration, Material Property (Electronic Structure ), and Structural Dynamics

6. Vibrational Spectroscopy Unique finger-printing capability of vibrational spectroscopy :  highly localized  well characterized by theory

7. Sum-frequency vibrational spectroscopy can be employed to reveal the interfacial molecular structure. Material properties are strongly affected by the structure and type of species on surface or at interface Smart Surface

8.  SFG:  SFG:  (2) eff =  (2) eff (bulk) +  (2) s (surface)  In a medium with an inversion symmetry:  (2) eff (bulk) = 0,  (2) s (surface)  0 Sum-frequency vibrational spectroscopy (SFVS) Resonance can be employed to yield sensitivity to molecular species.

9. Apparatus of sum-frequency vibrational spectroscopy (SFVS)---Laser System

10. Apparatus of sum-frequency vibrational spectroscopy

11. Sum-frequency vibrational spectroscopy of a LPUV- defined aligning layer for liquid crystal molecules

12. LCP on a LPUV-defined alignment layer Q (1515cm-1)=0.46 LCP Structure

13. Improving LCP Alignment on a LPUV-defined Surface

14. Improving LC Alignment with a LCP Coupling Layer on a LPUV-defined Surface

15. , which yields a uniform FLC alignment with Surface interactions can be used to unwind the spontaneous helix, which yields a uniform FLC alignment with Fast Response Fast ResponseBistability Wide Viewing Angle SSFLC and nc-ZnO doped SSFLC Tracking correlated motion of molecular fragments of LC materials: SSFLC and nc-ZnO doped SSFLC

16. FTIR Study of the Field-Induced FLC Switching Φ

17. Data Representation of 2D IR Asynchron. plot Synchron. plot

18. 2D IR Revealing Site Effect of Atomic Group Attached to Different Location on a Molecule Synchron. plot Asynchron. plot

19. Time-resolved FTIR for Snapshot of Molecular Dynamics

20. 2D IR Snapshots of Molecular Dynamics

21. Some real issues for optical microscopy at far field: 1. Increased transverse resolution Rayleigh criterion Δr = λ / (2NA) NA = numerical aperture = n sin θ 2. Increased longitudinal resolution Rayleigh criterion Δz = 2 λ / (NA) 2 (longitudinal resolution typically lower than transverse) 3. Ability to image through scattering medium Scattering leads to loss of contrast Scattering gets worse at shorter wavelengths New Modalities in Optical Microscopy

22. Current Methods for Increasing Spatial Resolution Microscope types: Widefield and Confocal

23.  The best resolution that can be obtained by diffraction-limited (200 nm) optical techniques is coarser than the molecular level by two orders of magnitude (2 nm).  Twofold improvements in resolution (approximately 100 nm) can be obtained in either confocal (4Pi) or widefield (I 5 M) technologies.  Super resolution beyond this resolution enhancement has been demonstrated using either saturation absorption coupled with structured illumination or stimulated emission depletion (STED). Current Status Nano-Optics is the study of optical phenomena and techniques beyond the diffraction limit

24. NLO and Superresolution: Saturated Structured-Illumination Microscopy (SSIM) A structured light interacts with fine patterns in the sample and creates a moiré effect. The fine patterns that were previously below the Abbe-Rayleigh limit can now be visualized as a moiré version. See: Mats G. L. Gustafsson, PNAS 102, 13081 – 13086 (2005) Object Structured Light Illuminated Object

25. Things Are Even Better by using Saturated Absorption ( SSIM ) Response of a saturable absorber to a sine-wave intensity modulation Here is what is happening in k-space

26. Typical Laboratory Result of SSIM A field of 50-nm fluorescent beads: (a) imaged by conventional microscopy, (b) linear structured illumination, and (c) saturated structured illumination using illumination pulses with 5.3 mJ/cm 2 energy density. Mats G. L. Gustafsson, PNAS 102, 13081 – 13086 (2005)

27. NLO and Superresolution: NLO and Superresolution: Stimulated Emission Depletion (STED) Microscopy Axial and transverse resolution better than 50 nm. Hell, Dyba, and Jakobs, Current Opinion in Neurobiology, 14:599, 2004.

28. STED Principle: an initial excitation pulse is focused on a spot. The spot is narrowed by a second, donut-shaped pulse that prompts all excited fluorophores to STED. This leaves only the hole of the donut in an excited state, and only this narrow hole is detected as an emitted fluorescence. The light doing the turning off is diffraction limited, and so it cannot provide any greater resolution alone. The trick is the saturated depletion, which helps to squeeze the spot down to a very small scale — in principle infinitely. The Abbe-Rayleigh Criteria Becomes:

29. Typical Laboratory Result of STED Imaging neurofilaments in human neuroblastoma. (left) Sub region of the confocal image after linear deconvolution (LD); (right) the deconvolved STED image to reveal object structures that are below 30 nm.

30. The principle of PALM:  A sparse subset of fluorescent molecules attached to proteins of interest are activated with a brief laser pulse at =0.405  m and then imaged at =0.561  m. This process is repeated many times until the population of inactivated, unbleached molecules is depleted.  The location of each molecule is determined by fitting the expected PSF to the actual molecular image. Repeating with all molecules across all frames and summing the results yields a superresolution image. Photoactivated Localization Microscopy (PALM) See: Eric Betzig, et al., SCIENCE 313, 1642 (2006)

31. Typical Result of PALM PALM image of dEosFP-tagged cytochrome-c oxidase localized within the matrix of mitochondria in a COS-7 cell is compared to its corresponding TEM image. Eric Betzig, et al., SCIENCE 313, 1642 (2006)

32. Probing into the nanoworld with femtosecond resolution Heterodyne Interferometric SNOM Lensed-fiber launched optical waveguide device under SNOM

33. Probing into the nanoworld with femtosecond resolution Verify the distributions of the amplitude and phase of an optical field at nanometer scale by combining SNOM and heterodyne fiber interferometry Signal intensities I s  1  10 -12 W  1  10 7 photons/sec are below the noise floor of photodiode detectors. By interfering this signal with I ref  1  10 -4 W, however, the signal at the detector is boosted to I s  1  10 -8 W, which is well within the detection limits of photo detectors.

34. FFT of the complex field corresponds to a projection in a basis of plane waves The spatial frequencies in the FFT spectrum are related to the propagation constants of the optical guided modes. Topography S

35. Tracking optical-field propagation in nanoworld N=38 (a) Triple-Line-Defect Transmittance (ar. un.) 20% Triple line defects 1m1m GaAs AlO SiO 2 Triple-Line Waveguide (provided by Prof. S. Y. Lin, RPI) Nano-Optics is the study of optical phenomena and techniques beyond the diffraction limit

36. Conclusions  Molecular vibrational spectroscopy is an effective technique to yield useful information about molecular structures and alignment.  New imaging modalities in optical microscopy have been developed to allow researchers probing into nano scale at the molecular level.  There are essentially no fundamental limit on how far we can go beyond the Abbe’s diffraction limit.