ultrafast terahertz kerr effect spectroscopy: detection of intramolecular vibrational coherences...
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Ultrafast Terahertz Kerr Effect Spectroscopy:Detection of Intramolecular Vibrational
Coherences
Marco Allodi, Ian Finneran, Geoffrey BlakeCalifornia Institute of Technology
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Nonlinear THz spectroscopy is very difficult!
Electronics Lasers (Photonics)
Sizov, Fedir F., et al. Optical Engineering 52.3 (2013)
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Multi-dimensional NMR
13C
1H
15N
1H2D-IR and optical experiments
2D Spectroscopies are nonlinear
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Milestones Necessary for 2D THz Spectroscopy
Generate Coherences
Manipulate Coherences
Detect Coherences
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Terahertz spectra are complicated, and sensitive to intermolecular structure
McGuire et al, in preparation.
Brett McGuire RI14
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Teraherz Kerr Effect
Hoffmann, M. C. et al. Appl. Phys. Lett., 2009, 95, 231105.
n
n = n + Δn
E
The only molecular, ultrafast, nonlinear THz spectroscopy
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The Optical Kerr Effect: Precursor to the Terahertz Kerr Effect
Δn ∝ E2
n
n = n + Δn
E
Zhong, Qin, and John T. Fourkas. "Optical Kerr Effect Spectroscopy of Simple Liquids†." The Journal of Physical Chemistry B 112.49 (2008): 15529-15539.
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REGENERATIVEAMPLIFIER
(Coherent Legend)
Ti:S 800 nm1 kHz>4 mJ35 fs
fs Ti:SaOSCILLATOR
Ti:S80 MHz~ 5 nJ
B.S.85:15
DETECTIONDELAY LINE
DETECTIONPHOTODIODEλ/4
WOLLASTONPRISM
OPASignal1450 nm
400 μJ
SAMPLE
OPTICALBEAM BLOCK
= 1450 nm= 800 nm= THz
LENSPOL
DSTMS THzEMITTER
THz Kerr Effect - Experimental Setup
Allodi, Finneran, & Blake, 2015 submitted.
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Heterdyne detection improves sensitivity
DETECTIONPHOTODIODESλ/ 4
WOLLASTONPRISM
SAMPLE
OPTICALBEAM BLOCK
LENSPOL
DSTMS THzEMITTER
WIRE-GRID POLARIZER
Image Credits: Rainbowphotonics.com
Allodi, Finneran, & Blake, 2015 submitted.
λ/ 2
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Heterodyne-Detected THz Kerr Effect Signal!
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Heterodyne-Detected THz Kerr Effect Signal!
Cuvette Response
Allodi, Finneran, & Blake, 2015 submitted.
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Intramolecular Vibrational Oscillations
Oscillations in CH2I2 match perfectly the 122 cm-1 ν4 mode.
Allodi, Finneran, & Blake, 2015, submitted.
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Vibrational excitation is possible at higher frequencies: CCl4
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Two field interactions allow excitation above 3 THz (100 microns)
CH2I2CCl4
Cuvette material is fused silica (Suprasil)
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The Optical Kerr Effect is Nonresonant
0 THz
time
7 THz
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There are many overdamped intermolecular vibrations at 3 THz!
0 THz
3 THz
6 THz
time
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Milestones Necessary for 2D THz Spectroscopy
✔ Generate Coherences
? Manipulate Coherences
✔ Detect Coherences
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Separate pulses will differentiate the excitation process
0 THz
3 THz
6 THz
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Conclusions & Future Directions
Heterodyne detection improves the sensitivity and allows phase-sensitive detection.
First nonlinear resonant terahertz vibrational coherences in a molecular liquid.
Multi-pulse schemes will reveal more information.
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Acknowledgments
The Blake Group
NSF