Transcript Slides - Jung Y. Huang

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.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.
 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.
SPATIAL RESOLUTION VS. CHEMICAL
INFORMATION
Rough estimates of the typical timescales associated
to the energies involved in molecular systems
Real-Space Configuration, Material Property
(Electronic Structure ), and Structural Dynamics
Vibrational
Spectroscopy
Unique finger-printing capability of
vibrational spectroscopy :
 highly localized
well characterized by theory
Material properties are strongly affected by the structure and
type of species on surface or at interface
Smart Surface
 Sum-frequency vibrational spectroscopy can be employed
to reveal the interfacial molecular structure.
Sum-frequency vibrational spectroscopy (SFVS)
Resonance can be employed
to yield sensitivity to molecular
species.
 SFG: (2)eff = (2)eff(bulk) + (2)s(surface)
 In a medium with an inversion symmetry:
(2)eff(bulk) = 0,
(2)s (surface)  0
Apparatus of sum-frequency vibrational
spectroscopy (SFVS)---Laser System
Apparatus of sum-frequency vibrational spectroscopy
Sum-frequency vibrational spectroscopy of a LPUVdefined aligning layer for liquid crystal molecules
(2)
(2)
(2)
Q  {2  zxx
(  00 ) [  zxx
(  00 )   zyy
(  900 )]  1}
 0.01
LCP on a LPUV-defined alignment layer
LCP Structure
Q (1515cm-1)=0.46
Improving LCP Alignment on a LPUV-defined
Surface
Improving LC Alignment with a LCP Coupling Layer
on a LPUV-defined Surface
Tracking correlated motion of molecular fragments of
LC materials: SSFLC and nc-ZnO doped SSFLC
Surface interactions can be used to
unwind the spontaneous helix, which
yields a uniform FLC alignment with
Fast Response
Bistability
Wide Viewing Angle
FTIR Study of the Field-Induced FLC Switching
Φ
Data Representation of 2D IR
Synchron. plot
Asynchron. plot
2D IR Revealing Site Effect of Atomic Group
Attached to Different Location on a Molecule
H2C
O
O
O
CN
O
O
CH3
H3C
Synchron. plot
Asynchron. plot
Time-resolved FTIR for Snapshot of Molecular
Dynamics
2D IR Snapshots of Molecular Dynamics
New Modalities in Optical Microscopy
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
Current Methods for Increasing Spatial Resolution
Microscope types:
Widefield and Confocal
Current Status
 The best resolution that can be obtained by diffractionlimited (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).
Nano-Optics is the study of optical phenomena
and techniques beyond the diffraction limit
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
Object
Structured
Light
See: Mats G. L. Gustafsson, PNAS
102, 13081–13086 (2005)
Things Are Even Better by using Saturated Absorption
Response of a
(SSIM)
saturable absorber to a
sine-wave intensity
modulation
Here is what is happening in k-space
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)
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.
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.
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.
Photoactivated Localization Microscopy (PALM)
See: Eric Betzig, et al., SCIENCE 313, 1642 (2006)
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.
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)
Probing into the nanoworld with femtosecond
resolution
Heterodyne Interferometric
SNOM
Lensed-fiber launched optical
waveguide device under SNOM
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 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.
Topography
S
Cos()
FFT of the complex field
corresponds to a projection in
a basis of plane waves
F (kz )  FFT [ S  Cos()]
The spatial frequencies in the FFT spectrum are related to
the propagation constants of the optical guided modes.
Tracking optical-field propagation in nanoworld
(a)
Triple-Line-Defect
SiO2
GaAs
Triple line defects
N=38
Triple line defects 1m
AlO
Triple-Line Waveguide (provided by Prof. S. Y. Lin, RPI)
Transmittance (ar. un.)
Ridge WG
30
20%
N=38
10
1
1600 1620 1640 1660 1680 1700
Wavelength (nm)
Nano-Optics is the
study of optical
phenomena and
techniques beyond the
diffraction limit
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.