Transcript Slides - Jung Y. Huang

Some Recent Advances in Spectroscopy beyond
Conventional Spectral Intensity Measurement
Jung Y. Huang 黃中垚
(http://www.jyhuang.idv.tw)
Department of Photonics, Chiao Tung University
March 23, 2008
Forward Problem in Solid-State Physics: Specifying the spatial
coordinates of all atomic species involved, and then calculating the
energy levels and wavefunctions (via DFT):
spatial coordinates of 
Atomic configuration 

all
atomic
species



osc. strength


damping constant, { }

i 
Electronic structure 

eigenvalues,
{

}
i


 eigenfunctions, { i } 
The relation between the band structure and the real-space atomic
configuration is non-intuitive, which makes the inverse problem
quite difficult.
A profound question in physics: Does a complete set of
spectral data contains enough information to determine
the geometrical structure?--- or Can we hear the shape of
a drum?
Spectral and wave function properties can be reflected
through optical susceptibility measurement. We are
therefore interested in retrieving the phase information
from the measured optical power spectrum in order to
recover the complete optical susceptibility.
Outline
Maximum-entropy phase-retrieval procedure for sumfrequency vibrational spectroscopy
Time-resolved two-dimensional infrared absorption correlation
spectroscopy of ferroelectric liquid crystal (FLC) without and
with a doping of zinc oxide nanoparticles
Active spectroscopy to guide the evolution of a complex system
and deduce the dynamic mechanism from the optimal laser field
used
Probing the molecular alignment on surface with Sum-Frequency
Vibrational Spectroscopy (SFVS)
Resonance can be employed to
make SFVS sensitive to molecular
species.
SFVS: 
(2)
eff
  (2)b (bulk )   (2) s ( surface)
On a medium with an inversion
symmetry:
 (2)b (bulk )  0,  (2) s ( surface )  0
Phase determination of optical susceptibility
1. Interferometry
2. Direct determination from optical
spectrum.
Phase determination of SFVS susceptibility with interferometry
Phase determination of SFVS susceptibility with interferometry
(2)
S ( s )   NR

q
Aq
(ir  q  i q )
2
Phase determination of nonlinear optical susceptibility
from a NLO spectrum
 Direct phase determination from
incomplete information with
maximum entropy principle
 No need for data extrapolation (such
as with Kramer-Kronig relations
 Maximize the spectral entropy under
the constraint of N measured spectral
points S(f)
h   log S ( f )df
f2
f1
Therefore, the MEM phase retrieval
problem is simplified to find the error
phase f(n)
A priori knowledge for MEM phase retrieval
To estimate the error phase, we propose:
Criterion A: For a spectrum with an isolated peak and
negligible background, the imaginary part of the NLO
susceptibility has a peak position the same as that of the
power spectrum S(f).
Criterion B: The real or the imaginary part of NLO
susceptibility should asymptotically approach to a
constant in region far away from resonance.
Criterion C: For an isolated peak, the imaginary part of the
NLO susceptibility is an even function relative to the
resonant frequency. Here the resonant frequency is
determined from the peak position of the power spectrum.
MEM for a multiple-peak IVSFG spectrum
IVSFG of
Silica/OTS/CCl4 interface
MEM for NLO spectrum with complex background:
IVSFG of H/C(111)
Different H coverages on
Diamond C(111) surface
NLO spectrum with complex background
S ( s )  
(2)
NR

q
Aq
(ir  q  i q )
2
NLO spectrum with complex background
 Top view along [111]
 Hydrogen coverage with isolated
dangling bonds = 1 (1  6  1 3)  1 3
monolayer
Outline
Maximum-entropy phase-retrieval procedure for sum-frequency
vibrational spectroscopy
Time-resolved two-dimensional infrared correlation
spectroscopy of ferroelectric liquid crystal (FLC) without
and with a doping of zinc oxide nanoparticles
Active spectroscopy to guide the evolution of a complex system
and deduce the dynamic mechanism from the optimal laser field
used
Motivation for the 2D IR study of SSFLC
 No single-species FLC can meet all application requirements,
which is true even for FLC mixture. Doping FLC with
nanomaterials can provide extra degree of freedom for tailoring
material properties.
 The application of SSFLC is often hindered by the mechanical
problem. The doping-induced binding effect may increase the
stability of the layer structure without sacrificing the fast
response characteristic of FLC.
Sample Preparation
 nc-ZnO (2Ro ~3.2 nm):
synthesized with wet chemistry 
behave like a molecular dopant
 Capping agent (l~0.6 nm): 3(Trimethoxysilyl) propyl
methacrylate (TPM)
 Doping Method: nc-ZnO nano
powder was mixed into FLC to 1
wt%.
 FLC: Felix 17/100
d  2   2n ; 1.9 m
@   632.8nm
Two-dimensional Vibrational Spectroscopy
Ultrashort laser had been used to probe
the internal workings of molecular
systems. A major development in this
area is a technique known as twodimensional vibrational spectroscopy,
which can reveal
 static structure of peptides and
proteins ;
 fast processes such as protein folding
and peptide conformational dynamics;
 the relationship between individual
bonds within or among molecular
species.
2D IR Correlation Spectroscopy
 2D IR emulates techniques used in NMR.
 However, molecular vibrational relaxation rates (in picoseconds) are
orders of magnitude faster than typical nuclei spin relaxation rates (in
sec). Therefore sub picosecond IR pulses shall be used in 2D IR to
monitor molecular structural evolution.
 We used a much slower process (with electric field and polarization
angle of the incident IR) to perturb the molecular system of interest.
 To generate 2D IR correlation plots, IR spectra were collected
sequentially as a function of the perturbing parameter.
2D Infrared Correlation Spectroscopy
Ap  A0  U  sin2 (  0 )
• By spreading peaks along the second
dimension, one can often sort out
C t (n 1 ,n 2 )   A (n 1 ;  ) A (n 2 ;  ) 
complex or overlapped spectral
features that cannot be detected along
 S t (n 1 ,n 2 )  iAt (n 1 ,n 2 )
the first dimension.
Synchronous
Asynchronous
Summary of the Synchronous and Asynchronous 2D IR
Correlation Plot
Ap  A0  U  sin2 (  0 )
Synchro. Plot: Information
Asynchro. Plot: Information
about the similarity in IR
azimuthal pattern.
about the dissimilarity in IR
azimuthal pattern.
Synchro. IR Correlation Reveals Uniaxial Alignment
 s (n 1 , n 2 )
nc-ZnO: FLC
nc-ZnO: FLC
FLC
FLC
Asynchro. IR Correlation Reveals Angular Deviation
 a (n 1 , n 2 )
FLC
nc-ZnO doped
FLC
Field-induced reorientation of SSFLC
Surface interactions unwind the
spontaneous helix, which then yields a
uniform FLC alignment with
sec Response
Bistability
Wide Viewing Angle
Time-resolved FTIR Spectroscopy
Tracking correlated motion of sub molecular fragments in an electro-optical
switching FLC mixture
Time-resolved azimuthal patterns of IR
absorption peaks at 1608 cm-1 (black) and
2924 (red) cm-1
Time-resolved 2D IR Correlation Spectroscopy
Tracking correlated motion of sub molecular fragments in an electrooptical switching FLC  (n , t; n , 0)
s
1
2
 Core groups:
Peaks of the
synchronous plot are
sensitive to both U and
0.
Pure SSFLC
nc-ZnO:SSFLC
Time-resolved 2D IR Correlation Spectroscopy
Tracking correlated motion of sub molecular fragments in an electrooptical switching FLC  s (n 1 , t; n 2 , 0)
 Functional groups on
alkyl-chain:
Pure SSFLC
Peaks of the
synchronous plot are
sensitive to both U
and 0.
nc-ZnO:SSFLC
Time-resolved 2D IR Correlation Spectroscopy
Tracking correlated motion of sub molecular fragments in an electrooptical switching FLC  a (n 1 , t; n 2 , 0)
 Core groups:
Cross-peaks of the
asynchronous plot
are sensitive to 0
only.
Pure SSFLC
nc-ZnO:SSFLC
Time-resolved 2D IR Correlation Spectroscopy
Tracking correlated motion of sub molecular fragments in an electrooptical switching FLC  a (n 1 , t; n 2 , 0)
 Functional groups on
alkyl-chain:
Pure SSFLC
Cross-peaks of the
asynchronous plot
are sensitive to 0
only.
nc-ZnO:SSFLC
2D IR Correlation Phase Angle
 Those stretching
modes associated
with the alkyl chains
have larger angular
spread than the core
groups.
 Doping SSFLC
with nc-ZnO results
in more concerted
orientational
switching at the sub
molecular level.
tan -1[ a (n 1 , t ;n 1 , 0)  s (n 1 , t ;n 1 , 0)]
Possible Origin of the Improved Ordering
U aZnO - LC
2
2
2CO
 ZnO
nFLC N ZnO
3


1000
J
/
m
3
3(4 0 )2 ( kBT ) R03 Rmax
By using an extrapolation
length of dc=100 nm
dc  | UaZnO- LC |: 1  104 J / m 2 : Af
An aligning effect comparable to that with a
strong anchoring surface!
Outline
Maximum-entropy phase-retrieval procedure for sum-frequency
vibrational spectroscopy
Time-resolved two-dimensional infrared absorption correlation
spectroscopy of ferroelectric liquid crystal (FLC) without and
with a doping of zinc oxide nanoparticles
Active spectroscopy to guide the evolution of a complex
system and deduce the dynamic mechanism from the
optimal laser field used
Control of a Material System with Ultrashort Light
 Go beyond the simple pump-probe spectroscopy by using the laser pulses
to influence the course of the molecular dynamics.
 This kind of work is usually carried out in a feedback loop with some form
of pulse shaping element controlled by a computer.
 An issue with coherent control is the inverse problem, i.e. how to retrieve
information about the system dynamics from the known optimal pulse.
 The core techniques needed include: (1) characterization of ultrafast pulses;
and (2) producing the pulses appropriate to the experiments.
Complete-field characterization of coherent optical pulses
Spectral-phase sensitivity defined as the difference of the
maximum and minimum of the signal varying as the phase
retardation of the specific spectral phase components
changes from 0 to 2π.
Complete-field characterization of coherent optical pulses
The freezing-phase algorithm can directly and rapidly yield
complete-field information with only three scans over the pulse
spectral range.

Complete-field characterization of coherent optical pulses
The freezing-phase algorithm can directly and rapidly yield
complete-field information.


Both the magnitude and spectral phase profiles of a coherent
optical pulse can be determined.
Complete-field characterization of coherent optical pulses:
freezing phase scheme
PLE of the DUT
Device under Test
1.00
R
Optical Reflectivity
(c)
Pulse
spectrum
0.50
0.00
1.15
1.20
1.25
1.30
Wavelength (m)
1.35
1.40
Complete-field characterization of coherent optical pulses:
freezing phase scheme
d-QW: double Ga0.47In0.53As quantum wells
embedded in a /4-thick Al0.48In0.52As layer;
QD-/4: self-assembled InAs quantum-dots
embedded in a /4-thick GaAs layer;
QD-/2: self-assembled InAs quantum-dots
embedded in a /2-thick GaAs layer
Coherent-controlled nonlinear optical microscopy
Coherent control contrast enhancement as large as a
factor of three can be achieved at regions where the PL
peak wavelengths differ only 18 nm.
spectrometer
Input pulses
Beam splitter
Objective
lens
SLM
sample
XY scanning stage
Coherent and incoherent multiphoton processes in SBR
Theory
PL
SHG
THG
Exp.
Coherent-controlled nonlinear optical microscopy
Coherent control offers an additional degree of freedom
to distinguish coherent and incoherent nonlinear optical
processes.
Spectral-phase sensitivity curves of two-photon fluorescence
(TPF) and the corresponding phase profiles with the maximum
TPF signal from the position P and S.
The corresponding TPF spectra from the position-P, and S are
presented.
Characterize Material System via Quantum Control
Future Development: Quantum-control technique for probing
molecular recognition mechanism of Biomolecules.
optimized
anti-optimized
Important Question: What is the
characteristic frequency among
these binding nano objects?
Conclusions
A MEM phase retrieval procedure had been successfully
developed to yield complex susceptibility from the measured
SFG power spectrum.
Time-resolved 2D IR correlation spectroscopy had been used
to reveal intra- and intermolecular motions in an electrooptical switching FLC.
Control molecular response by laser pulses beyond simple
pump-probe scheme is possible via coherent control
technique.