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Fourier-transform coherent anti-Stokes Raman scattering microscopy
Jennifer P. Ogilvie et al. Opt. Lett. 31, 480 (2006)
Kazuya MORI
MIYASAKA Lab.
Contents
Introduction ・ Raman Scattering ・ Coherent Anti-Stokes Raman Scattering (CARS) ・ Nonresonant background problem ・ Motivation Fourier-transform CARS (FTCARS) method Experimental Setup using a femtosecond laser Results and Discussion ・ CARS imaging of polystyrene bead Summary
http://www.nanophoton.jp/raman/raman-11.html
microscopy
Molecular vibrationAnti-Stokes Raman Scatteringωvib
Stokes Raman Scattering
Rayleigh scattering
Incident light
ν0
ν0+ωvib
ν0
ν0-ωvib
ωvib
Virtual state
+Raman Scattering
Stokes Anti-Stokes
Energy diagram
Raman Scattering
Introduction
excellent ”molecular fingerprint” for their identification
分子振動
ラマン散乱
nucleic acid protein lipid Raman spectra
Introduction
Coherent Anti-Stokes Raman Scattering (CARS)
But Raman scattering is・・・・ very weak signal (~10-6 of incident
radiation)・ difficult to separate from fluorescence
Molecular vibration
ωvib
ω1
beam2
beam1
ωvibω2
ω3= 2ω1 – ω2
(pump, probe)
(stokes)
ω1
ω1
ω2
ω3
・ significant signal enhancement over Raman scattering・ Anti-Stokes field → fluorescence-free
Nonresonant (NR) background Problem
Introduction
ωvib ωvib
ω’vib
Raman spectra of polystyrene beads conventional Raman microscope CARS microscope
NR background signal diagram
Near two-photon resonance
far from two-photon resonance
low resolution ( 30cm-
1)and spectral shift
非共鳴
M. Hashimoto et. al. Opt. Lett. 25, 1768-1770 (2000)
Motivation
NR background Limited fingerprint region imaging Complex setup
Problem
a new method for CARS microscopy with high resolution using a single femtosecond pulse laser
Single femtosecond pulse laser
Fourier-transform CARS (FTCARS) method
two femtosecond pulse
ωvib
time-domain
Time delay τ/ fs
vibrational polarization + ② Time-domain CARS signal振動分極
stokespump
probe
① ②
CARS
τ
delay
Fourier-transform CARS (FTCARS) method
Fourier-transform
frequency-domaintime-domain
Time delay / fs frequency / cm-1
CARS spectrafrequency-domain spectra =
NR background
Fourier-transform
vibrational polarization
=Molecular vibration
)(tx
frequencies
dtetxX ti )()(
)(X
(electronic response)
dteXtx ti)()(
Experimental Setup
~820nm Pulse duration ~20fs
PC: prism compressor
LPF: long-pass filter(>780nm)
SPF: short-pass filter(<760nm)
BS: beam splitter
DBS: dichroic beam splitter
PMT: photomultiplier tube
fluorescence
CARS signal
delay
光電子増倍管
ω3= 2ω1 – ω2
ω1
ω2 Phase matching 2k1k2
k3
Conventional CARS CARS microscopy
ω3ω1
ω2(CARS)
Filter spatially-resolved
spectral filtering
Results and Discussion
HC
H2C
NR background
Sample
20μm polystyrene bead
in 2-propanol
time-domain
vibrational polarization
Time delay (fs)
ampl
itude
(a.
u.)
H3CHC CH3
CH3
2-propanolpolystyrene
Results and Discussion
FTCARS imaging
FTCARS offers high spectral resolution ~13cm-1
Scan
1005cm-1 → C-C stretching mode in polystyrene816cm-1 → C-C stretching mode in 2-propanol
Summary
A Fourier-transform technique for CARS microscopy that employs a single laser source and time-delay setup was proposed.
FTCARS method was demonstrated by spectrally imaging a polystyrene bead in 2-propanol.
FTCARS microscopy offers a compact optical setup and high spectral resolusion(~ 13cm-1).
ω2
Frequency / cm-1
femtosecond pulse
ω1
time/ fs
uncertainty principle ΔEΔt~ħ
stokespump
probe
① ②
CARSω1ω2
Spontaneous Raman spectrum of polystyrene
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
HC
H2C
Sample
Sample
Spontaneous Raman spectrum of 2-propanol
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
H3CHC CH3
CH3
http://www.bangslabs.com/cgi-bin/PSGFind.pl?return=6.2&code=FC07F
Fluorescent dye
Sample
photomultiplier tube (光電子増倍管)
http://ja.wikipedia.org/wiki/%E7%94%BB%E5%83%8F:Photomultipliertube.png