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Femtosecond Coherent Control for Precision Nonlinear Spectroscopy

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Femtosecond Coherent Control for Precision Nonlinear Spectroscopy. D. Oron, N. ... Xenopus embryo. fossil. Yeast cell. THG images of biological specimen ... – PowerPoint PPT presentation

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Title: Femtosecond Coherent Control for Precision Nonlinear Spectroscopy


1
Femtosecond Coherent Control for Precision
Nonlinear Spectroscopy
D. Oron, N. Dudovich and Y. Silberberg, Physics
of Complex Systems Weizmann Institute of
Science Rehovot, Israel
CREOL, April 2004
2
Narrow transitions induced by broad band pulses
Loss of spectral resolution
3
Quantum Coherent Control
4
Simplest nonlinear interactionTwo photon
absorption
Nonresonant TPA
I
5
Nonresonant TPA
All the paths are in-phase
Transform-limited pulses maximize transition
rates Antisymmetric phase functions maintain
efficiency
6
Energy level structure of Cesium
7
Nonresonant TPA Control Experimental results
Step location/bandwidth
Antisymmetric phase has no effect on transition
probability Specific spectral phase mask can
annihilate the absorption rate ?Selective
excitation
Meshulach Silberberg, Nature, 396, 239
(1998),Phys. Rev. A 60, 1287 (1999)
8
Two photon absorption
II
9
Angular momentum control
Px
Py
ExEx transitions
Brixner and Gerber, Opt. Lett. 26, 557 (2002)
Two degenerate orthogonal states can be
separately controlled
10
Separate control of non-interfering paths
?
Px
Py
Ey
Ex
Phase and polarization
Phase mask
Ex
Ex
N. Dudovich, D. Oron and Y. Silberberg, accepted
for publication in Phys. Rev. Lett. (2004).
11
Nonlinear laser scanning microscopy
  • Multiphoton microscopy enables inherent optical
    sectioning capabilities due to nonlinear nature
    of the process. Signal originates only from the
    focal spot.
  • NIR illumination enables imaging through
    scattering samples
  • Typically applied as laser scanning microscopy in
    which the sample is scanned point by point.
  • First demonstrations
  • CARS microscopy Duncan et al., Opt. Lett. 7, 350
    (1982)
  • two-photon fluorescence microscopy Denk et al.,
    Science 248, 73 (1990).
  • Extended to coherent processes
  • SHG Peleg et al., Bioimaging 4, 215 (1996).
  • THG Barad et al., Appl. Phys. Lett. 70, 922
    (1997).
  • CARS (revisited) Zumbucsh et al., Phys. Rev.
    Lett. 82, 4142 (1999)

12
Laser scanning microscopy - setup
Photomultiplier tube
lock-in amplifier
computer
filter
condenser
z
sample
y
x
microscope objective
Optical scanners
femtosecond laser source
13
THG images of biological specimen
fossil
Yeast cell
Mouse bone
Xenopus embryo
Drosophila ovary
14
Optical sectioning capabilities
Optical sections of a neuron
Sections separated by 1mm
Yelin et al., Appl. Phys. B 74, S97 (2002)
15
Coherent Anti-Stokes Raman Scattering (CARS)
  • In a CARS process a pump and a Stokes photon
    coherently excite a vibrational level. A probe
    photon interacts with the excited level to emit a
    signal photon.
  • Large, directional and coherent signal (compare
    to Raman scattering).
  • Attractive for microscopy applications
  • -provides a vibrational imaging with 3D
  • sectioning capability.

16
Single Pulse CARS
When the pulse duration is shorter than the
vibrational period of the molecule, the CARS
process can be induced within a single pulse.
The spectral resolution of this process is
limited by the pulse bandwidth High nonresonant
background
17
Resonant vs. Nonresonant CARS
Resonant CARS is always accompanied by a
nonresonant background
Nonresonant background is maximal for transform
limited pulses (highest peak intensity)
Usually dealt with by using longer pulses and by
polarization techniques
18
CARS Selective Excitation
Transform-limited pulses maximize transition
rates Periodic phase functions maintain
efficiency
Weiner et al., Science 273, 1317 (1990) Oron et
al., Phys. Rev. A 65, 043408 (2002) Gershgoren et
al., Opt. Lett. 28, 361 (2003)
19
Single-pulse CARS with periodic phase
20
Single-pulse CARS with periodic
phaseSpectroscopy by selective excitation
Spectral phase
Temporal profile
Population amplitude (monitor 577cm-1 level)
21
Single-pulse CARS experimental setup
N. Dudovich, D. Oron and Y. Silberberg, Nature
418, 512 (2002).
22
CARS spectroscopy
Spectrocopy in the fingerprint region
Modulated spectral phase function
t
  • Reduced nonresonant background
  • Spectral resolution 30 cm-1, 70 times the pulse
    band width

N. Dudovich, D. Oron and Y. Silberberg, J. Chem.
Phys. 118, 9208 (2003).
23
Multiplexed CARS
Measured signal is heterodyned with the
nonresonant background
From Muller et al., JPC B 106, 3715 (2002)
24
Single-pulse Multiplexed CARS
25
Experimental set-up phase and polarization shaping
Brixner and Gerber, Opt. Lett. 26, 557 (2002)
26
Narrow probing by an orthogonal polarization
D. Oron, N. Dudovich and Y. Silberberg, Phys.
Rev. Lett. 90, 213902 (2003).
27
Narrow probing by phase and polarization shaping
Contribution only by
28
Extracted Raman spectrum
D. Oron, N. Dudovich and Y. Silberberg, Phys.
Rev. Lett. 90, 213902 (2003).
29
All-optical analysis of Raman spectra
Use broadband probing to induce interferences
between contributions from several Raman levels
30
All-optical analysis of Raman spectra
application to spectroscopy of 1,2 dichloroethane
31
Summary
  • Spectral resolution orders of magnitude higher
    than the pulse bandwidth is achieved in nonlinear
    spectroscopy by applying spectral phase and
    polarization manipulations.
  • Nonresonant background can be suppressed,
    directed to an orthogonal channel or used as a
    local oscillator, to enhanced the
    signal/background ratio.
  • Coherent control schemes developed for simple
    quantum systems can be utilized as the "building
    blocks" to control various multiphoton
    transitions.

32
Nonresonant background reduction
glass
Ba(NO3)2
n1
n2
Relative intensity
n4
Pulse train duration fs
Nonresonant reduction by a factor of 250
Dudovich et al., J. Chem. Phys. 118, 9208 (2003)
33
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34
Angular distribution control
Experimental results
Simulation
N. Dudovich, D. Oron and Y. Silberberg, accepted
for publication in Phys. Rev. Lett. (2004).
35
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36
Femtosecond pulses motivations and main drawbacks
  • Short duration ? Measuring fast evolving
    processes.
  • High peak intensity ? efficient for multiphoton
    transitions.
  • Large spectral bandwidth ? provide wide band
    spectroscopic information.

However
  • In resonant nonlinear transitions two time scales
    are involved
  • ? and the life time of the resonant level (ps in
    molecules or ns in atoms)
  • Lost of spectral resolution
  • Large nonresonant signal

37
Separate control of non-interfering paths
Px
Py
Ey
Ex
Phase and polarization
Phase mask
Ex
Ex
N. Dudovich, D. Oron and Y. Silberberg, accepted
for publication in Phys. Rev. Lett. (2004).
38
Multiplex CARS Phase control
  • Multiplex scheme narrow spectral phase
    manipulation.
  • Sign inversion around the resonance ? narrow
    enhancement of the signal can be achieved by
    applying ? phase window

39
CARS spectrum Narrow probing
Nonresonant Background from overlap of the pump
and probe
40
Narrow probing by an orthogonal polarization
D. Oron, N. Dudovich and Y. Silberberg, Phys.
Rev. Lett. 90, 213902 (2003).
41
Weiner et al., Science 273, 1317 (1990) Oron et
al., Phys. Rev. A 65, 043408 (2002) Gershgoren et
al., Opt. Lett. 28, 361 (2003)
42
Impulsive excitation
Weiner et al., Science 273, 1317 (1990)
43
Impulsive excitation
Weiner et al., Science 273, 1317 (1990)
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