1. California Institute of Technology
Ultrafast Terahertz Kerr Effect Spectroscopy of Aromatic Liquids
5:47
Ian Finneran, Marco Allodi, Geoffrey Blake
California Institute of Technology

2. The Kerr Effect is over 100 years old!
DC Kerr Effect
~ms-ns
Optical (AC) Kerr Effect
~fs E +V n n
n = n0 + Δn
Δn ∝ E2
1963
Mayer, Gires, Maker,
Terhune, Savage
1875
John Kerr

3. The Kerr Effect is Useful for Chemistry
Optical Kerr Effect
(~375 THz)
Dynamic Kerr Effect
(<0.1 THz)
H2O
μ(t)
Π(t)
Beevers, M. S., et al. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics (1976)
Bartolini, Paolo, et al. Springer

4. The intermediate response is not fully understood
Short
Response
(Electronic)
The intermediate response is not fully understood
Intermediate
Response
Long Response
(Collective Reorientation)

5. Nonlinear THz spectroscopy is very difficult!
Lasers (Photonics)
Electronics
Hard to get good pop inversion with small bandgap for photonics
Sizov, Fedir F., et al. Optical Engineering 52.3 (2013)

6. Terahertz Kerr Effect: Nelson Lab 2009
Picosecond dynamics E n
n = n + Δn
Δn ∝ E2
Hoffmann, Matthias C., et al. "Terahertz Kerr effect." Applied Physics Letters (2009):

7. Terahertz Kerr Effect: Nelson Lab 2009
Hoffmann, Matthias C., et al. "Terahertz Kerr effect." Applied Physics Letters95.23 (2009):

8. THz Kerr Effect - Experimental Setup
= 1450 nm
fs Ti:Sa
OSCILLATOR
Ti:S
80 MHz
~ 5 nJ
= 800 nm
= THz
REGENERATIVE
AMPLIFIER
(Coherent Legend)
Ti:S
800 nm
1 kHz
>4 mJ
35 fs
----- Meeting Notes (5/22/15 16:45) -----
Discuss Alignment of Molecules
DSTMS THz
EMITTER
B.S.
85:15
DETECTION
DELAY LINE
OPTICAL
BEAM BLOCK
OPA
Signal
1450 nm
400 μJ
POL
LENS
SAMPLE
DETECTION
PHOTODIODE
λ/4
WOLLASTON
PRISM
Allodi, Finneran, & Blake, 2015 under review.

9. THz Kerr Effect - Experimental Setup
DSTMS THz
EMITTER
Discuss Heterodyne
OPTICAL
BEAM BLOCK
WIRE-GRID POLARIZER
POL
LENS
SAMPLE
DETECTION
PHOTODIODES
λ/ 2
λ/ 4
WOLLASTON
PRISM
Allodi, Finneran, & Blake, 2015 under review.
Image Credits: Rainbowphotonics.com

10. Electronic
Orientational

11. The Instrument Response is over after 2 ps
Probe Pulse = ~40 fs

12. The Orientational Response is Dependent on Structure

13. Intermediate Response is clear near 5 ps

14. Hexafluorobenzene: a double exponential is needed to fit data
𝜒 𝑟𝑒𝑑 2 =1.0
𝜒 𝑟𝑒𝑑 2 =6.6
TKE
tor= 13.88(5) ps
tint= 2.15(5) ps
Aor = 0.57(1)
Ratio
tor: 1.1
tint: 0.8
Aor: 0.7
Aor=1-Aint
OKE [1]
tor= 13.3(1) ps
tint= 2.9(1) ps
Aor = 0.88
[1] Loughnane, Brian J., Alessandra Scodinu, and John T. Fourkas. "Temperature-dependent optical Kerr effect spectroscopy of aromatic liquids." The Journal of Physical Chemistry B (2006):

15. Conclusions
TKE is likely complementary to OKE. There is an intermediate TKE response. Need more modeling!! For all samples studied:
𝐴 𝑜𝑟 𝑇𝐾𝐸 < 𝐴 𝑜𝑟 𝑂𝐾𝐸

16. Acknowledgments
NSF
The Blake Group