Ultrafast Terahertz Kerr Effect Spectroscopy:Detection of Intramolecular Vibrational

Coherences

Marco Allodi, Ian Finneran, Geoffrey BlakeCalifornia Institute of Technology

Nonlinear THz spectroscopy is very difficult!

Electronics Lasers (Photonics)

Sizov, Fedir F., et al. Optical Engineering 52.3 (2013)

Multi-dimensional NMR

13C

1H

15N

1H2D-IR and optical experiments

2D Spectroscopies are nonlinear

Milestones Necessary for 2D THz Spectroscopy

Generate Coherences

Manipulate Coherences

Detect Coherences

Terahertz spectra are complicated, and sensitive to intermolecular structure

McGuire et al, in preparation.

Brett McGuire RI14

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

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.

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.

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

Heterodyne-Detected THz Kerr Effect Signal!

Heterodyne-Detected THz Kerr Effect Signal!

Cuvette Response

Allodi, Finneran, & Blake, 2015 submitted.

Intramolecular Vibrational Oscillations

Oscillations in CH2I2 match perfectly the 122 cm-1 ν4 mode.

Allodi, Finneran, & Blake, 2015, submitted.

Vibrational excitation is possible at higher frequencies: CCl4

Two field interactions allow excitation above 3 THz (100 microns)

CH2I2CCl4

Cuvette material is fused silica (Suprasil)

The Optical Kerr Effect is Nonresonant

0 THz

time

7 THz

There are many overdamped intermolecular vibrations at 3 THz!

0 THz

3 THz

6 THz

time

Milestones Necessary for 2D THz Spectroscopy

✔ Generate Coherences

? Manipulate Coherences

✔ Detect Coherences

Separate pulses will differentiate the excitation process

0 THz

3 THz

6 THz

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.

Acknowledgments

The Blake Group

NSF