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

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

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 2008. 73-127.

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

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)

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 95.23 (2009): 231105.

Terahertz Kerr Effect: Nelson Lab 2009 Hoffmann, Matthias C., et al. "Terahertz Kerr effect." Applied Physics Letters95.23 (2009): 231105.

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.

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

Electronic Orientational

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

The Orientational Response is Dependent on Structure

Intermediate Response is clear near 5 ps

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 110.11 (2006): 5708-5720.

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

Acknowledgments NSF The Blake Group