F rom nanometers to femtoseconds : the impact on optical science

1. From nanometers to femtoseconds:the impact on optical science Jung Y. Huang Department of Photonics, Chiao Tung University Hsinchu, Taiwan December 7, 2007

2. The Target of University R&D: create revolution technology breakthrough

3. Milestones of Science Criteria that mark a progress as milestone of science: • A new technological development that lets scientists do things that they never could before the advance; or • A discovery that brings into play a whole assembly of new technology which lets scientists do something that they would very much like to do.

5. The first quantum revolution In the first quantum revolution, quantum mechanics was developed to help understanding what already exists.  We can use it to explain the periodic table, but not design and build our own atoms.

6. The second quantum revolution • The difference between science and technology is the ability to engineer your surroundings to fit into your own needs, and not just explain them. • We are approaching to an era that actively employs quantum mechanics to alter the face of our physical world. • Quantum technology allows us to organize and control the inner components of a complex system governed by the laws of quantum physics.

7. The essence of quantum technology • Successful technologies are based on precise engineering, which requires high-precision measurement. Quantum technology will require us to develop a quantum metrology to enable new types of high-precision measurement. [See Science 306, No 5700 (2004)] • No complex technology can function without incorporating control systems with feedback, feed-forward, and error correction capability. Control systems take as input a measurement record, perform complex signal analysis in the presence of noise, and use the information gained to adapt the dynamics of the system ( quantum control). • Decoherence is the main stumbling block in turning a quantum computer from theoretical dream to practical reality. The loss of coherence is one of the crucial reasons why macroscopic objects never show quantum phenomena (such as interference). Because they are so big that they interact strongly with the environment and lose their coherence very quickly.

8. Definition of nanotechnology The technology platform of the second quantum revolution  Nanotechnology Nanotechnology is dealing with functional systems based on the use of subunits with specific size-dependent quantum mechanical properties. A functional system may be described as a collection of a certain number of interacting subunits forming a new entity with specific system properties. The subunits shall be combined in a directed manner and are hierarchically organized on different levels of complexity.

9. Current scientific research throughout the natural sciences aims at the exploration of the collectivity of structures with dimensions between 1 nm and 100 nm (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.

10. The size dependence of the properties becomes evident when they • no longer follow classical physical laws but rather are described by quantum mechanical ones Nano-effects dominated by a quantum mechanical behavior. • are dominated by particular interface effects Nano-effects dominated by interface effects. • exhibit properties due to a finite number of ordered constituents.

11. Nano-effects dominated by a quantum mechanical behavior Some basic physics • Density of states (DoS) in 3D:

12. Discrete States in 3D Confinement: Quantum Dots • For 3D infinite potential boxes

13. Optical Properties of Quantum Dots Quantum dots are ideal tools for multiplexed fluorescent detection. All of the quantum dots can be excited with a common light source. The colors of these materials are dictated by the size and material they are made from. An almost unlimited array of colors across the visible and into the infrared are possible. (Quantum Dot Corp.)

14. Nano-scaled properties dominated by nano-scaled interface effects Si quantum dots embedded in mesoporous silica

15. Enhanced photoresponsivity of Si quantum dots embedded in mesoporous silica with interface phonon coupling

17. Sum-Frequency Vibrational Spectroscopy with • unique finger-printing capability : • highly localized • well characterized by theory One side-bonded Si QDs grown by ICP in self-assembled mesoporous silica provide oriented interface bonding geometry to generate ferroelectric, which is impossible to yield from bulk Si.

18. n-Type p-Type _ _ _ _ _ _ _ _ + + + + + + pn-junction + + Enhanced Electro-Optical Response from Engineered Architectures with Self Assembling Nanotechnology • Motivation of the Research: Exploring the feasible ways to realize functional materials with enhanced EO responses from interacting subunits combined in a hierarchically organized structure. • The enhanced EO properties can be considered to originate from a combined effect of enhanced charge transport and enhanced light emission.

19. I. Enhanced Charge Transport System 1:Enhanced electron transport through ordered nc-CdS constituents in the PV4P nanodomains of PS-b-P4VP copolymer Major Achievement:The electron transport via CdSe QDs confined in the poly(4-vinylpyridine) nanodomains at 48vol% was found to be 10 times larger than that in a random distribution. Chung-Ping Li, Kung-Hwa Wei and Jung Y. Huang: “Enhanced Collective Electron Transport by CdSe Quantum Dots Self-Assembled in the Poly(4-vinylpyridine) Nanodomains of a Poly(styrene-b-4-vinylpyridine) Diblock Copolymer Thin Film” -Angewandte Chemie International Edition 45, 1-5 (2006).

20. Quasi 3D Quasi 1D e- e- System 2:Enhanced electron transport in a limited number of ordered nc-Au constituents in the PV4P nanodomains of PS-b-P4VP copolymer An example to illustrate a hierarchically organized nanostructure with different levels of complexity

21. SPATIAL RESOLUTION VS. CHEMICAL INFORMATION

22. Some real issues for optical microscopy at far field: New Modalities in Optical Microscopy 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

23. Current Methods for Increasing Spatial Resolution

24. Current Status • 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 (I5M) technologies. • Super resolution beyond this resolution enhancement has been demonstrated using either saturation absorption coupled with structured illumination or stimulated emission depletion (STED).

25. 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. Illuminated Object Structured Light Object See: Mats G. L. Gustafsson, PNAS 102, 13081–13086(2005)

26. 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

27. 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/cm2 energy density. Mats G. L. Gustafsson, PNAS 102, 13081–13086(2005)

28. 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.

29. The Abbe-Rayleigh Criteria Becomes: 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.

30. 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.

31. Photoactivated Localization Microscopy (PALM) See: Eric Betzig, et al., SCIENCE 313, 1642 (2006) The principle of PALM: • A sparse subset of fluorescentmolecules attached toproteins 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.

32. 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)

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

34. Probing into the nanoworld with femtosecond resolution • Verify the distributions of the amplitude and phase of an optical field at the nanometer scale by combining SNOM and heterodyne fiber interferometry Signal intensities Is 110-12 W 1107 photons/sec are below the noise floor of photodiode detectors. By interfering this signal with Iref110-4 W , however, the signal at the detector is boosted to Is110-8 W , which is well within the detection limits of photo detectors.

35. Topography S 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.

36. (a) Triple-Line-Defect N=38 Tracking optical-field propagation in nanoworld fs pulse propagation Y. Fainman Group at UCSD Triple-Line Waveguide (provided by Prof. S. Y. Lin, RPI) Nano-Optics is the study of optical phenomena and techniques beyond the diffraction limit

37. Tracking optical field propagation in nanoworld S N. F. van Hulst

38. The detection of de-coherence and primary events in the time evolution of many complex systems (physical, chemical or biological)require a femtosecond temporal resolution. Further consider this issue from (1) temporal scales, (2) energy,and (3) power density Why do we need ultrashort optical pulses ?

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

41. There are clear advantages of producing and using optical pulses of a few femtoseconds to study the dynamics of chemical and biological molecules as well as a variety of materials in condensed matter physics. But there is more than just temporal considerations!

42. Time versus frequency domains

43. Energy Density of Electromagnetic Field

44. Self phase modulation: generation of white light continuum

45. Most chemical reactions occur in femtoseconds (10-15 sec) Femtosecond spectroscopy monitoring reactions in real time (Femtochemistry, A. H. Zewail, 2004 Nobel Laureate in Chemistry) Short pulse duration allows the detection of short-lived transient chemical reactions Femtosecond Spectroscopy

46. Pump-and-Probe Scheme • Medium is excited with femtosecond pulse • Delayed probe pulse by increasing path length • Short pulse duration allows short-lived reactions to be studied • Very high temporal resolutions

47. Photocycle of bateriorhodopsin Biological molecules have evolved to efficiently convert energy from one form to another. Dissipation of molecular vibrational excitation energy typically takes place on picosecond time scales, so biological molecules must be able to channel energy rapidly and efficiently if they are to be able to direct it in a useful manner.

48. Absorption of a visible photon is followed by rapid motion out of the Franck-Condon region along high-frequency HOOP coordinates (vibrational period 36 fs) which carry the system toward a conical intersection in 50 fs. Curve crossing to the ground state to form highly distorted photo-rhodopsin is complete by 200 fs. • The structural evolution of retinal on the ground-state surface along the C11=C12 torsional as well as other coordinates produces all-trans bathorhodopsin in 1 ps. • The reaction is extremely efficient, with a quantum yield of 0.65, and about 60% of the incident photon energy is stored in the first thermodynamically stable all-trans retinal photoproduct. This stored energy is then used to drive conformational changes in the G protein–coupled receptor that eventually lead to visual sensation.

49. What we have learn from science and basic research • Science is about questions, research is about answers. Great questions make good science. • Science’s great advances occur on the frontiers, at the interface between the ignorance and knowledge, where the most profound questions are posed. • We are standing before a great opportunity of quantum technology, molecular biology, and new energy technology. There are a plenty of opportunitues ahead!