Hyper–Rayleigh scattering

Hyper–Rayleigh scattering Optical Activity (/ˈreɪli/ RAY-lee), (a form of Chiroptical harmonic scattering) is a nonlinear optical physical effect whereby chiral scatterers (such as nanoparticles or molecules) convert light (or other electromagnetic radiation) to higher frequencies via harmonic generation processes, in a way that the intensity of generated light depends on the chirality of the scatterers. "Hyper–Rayleigh scattering" is a nonlinear optical counterpart to Rayleigh scattering. "Optical activity" refers to any changes in light properties (such as intensity or polarization) that are due to chirality.

Diagram of the first observation of the Hyper Rayleigh Scattering Optical Activity effect, from silver helical nanoparticles, upon illumination with circularly polarized light at frequency ω.

History

The effect was theoretically predicted in 1979,[1] in a mathematical description of hyper Raman scattering optical activity. Within this theoretical model, upon setting the initial and final frequencies of light to the same value, the mathematics describe the Hyper Rayleigh Scattering Optical Activity. The theory was well in advance of its time, and the effect remained elusive for 40 years. Its author David L. Andrews referred to it as the "Impossible Theory". However, in January 2019, an experimental demonstration was reported by Ventsislav K. Valev and his team.[2][3] The team investigated the hyper Rayleigh scattering (at the second harmonic generation frequency) from chiral nanohelices made of silver. Valev and his team observed that the intensity of the hyper Rayleigh scattering light depended on the direction of circularly polarized light and that this dependence reversed with the chirality of the nanohelices. Valev's work unambiguously established that the effect is physically possible, opening the way for nonlinear chiroptical investigations of a variety of chiral light-scattering materials; including molecules,[4] plasmonic metal nanoparticles[5] and semiconductor nanoparticles.[6]

Significance

Hyper Rayleigh Scattering Optical Activity (HRS OA) is arguably the most fundamental nonlinear chiral optical (chiroptical) effect; since other nonlinear chiroptical effects have additional requirements, which make them conceptually more involved, i.e. less fundamental. HRS OA is a scattering effect and therefore it does not require the frequency conversion process to be coherent; contrary to other nonlinear chiroptical effects, such as Second Harmonic Generation Circular Dichroism[7] or Second Harmonic Generation Optical Rotation.[8] Moreover, HRS OA is a parametric process (optics): the initial and final quantum mechanical states of the excited electron are the same. Because the excitation proceeds via virtual states, there is no restriction on the frequency of incident light. By contrast, other nonlinear scattering effects, such as two-photon circular dichroism and hyper-Raman are non-parametric - they require real energy states that restrict the frequencies at which these effects can be observed.

In molecules

Soon after the first demonstration of Hyper Rayleigh Scattering Optical Activity in metal nanoparticles,[3] the effect was replicated in organic molecules, specifically aromatic oligoamide foldamers.[4]

At the third harmonic

Whereas the initial experimental demonstration of hyper-Rayleigh scattering optical activity was observed at the second harmonic of the illumination frequency of light, the effect is general and can be observed at higher harmonics. The first demonstration of hyper Rayleigh scattering optical activity at the third harmonic was reported by Valev’s team in 2021, from sliver nanohelices.[9]

See also

References
  1. Andrews, D.L.; Thirunamachandran, T. (1979). "Hyper−Raman scattering by chiral molecules" (PDF). J. Chem. Phys. 70 (2): 1027. doi:10.1063/1.437535.
  2. ""Impossible" UEA physics theory proven in practice after 40 years - News - UEA". www.uea.ac.uk. Retrieved 2020-04-13.
  3. Collins, J.T.; Rusimova, K.R.; Hooper, D.C..; Jeong, H.-H.; Ohnoutek, L.; Pradaux-Caggiano, F.; Verbiest, T.; Carbery, D.R.; Fischer, P.; Valev, V.K. (2019). "First Observation of Optical Activity in Hyper-Rayleigh Scattering". Physical Review X. 9: 011024. doi:10.1103/PhysRevX.9.011024.
  4. Verreault, D.; Moreno, K.; Merlet, E.; Adamietz, F.; Kauffmann, B.; Ferrand, Y.; Olivier, C.; Rodriguez, V. (2019). "Hyper-Rayleigh Scattering as a New Chiroptical Method: Uncovering the Nonlinear Optical Activity of Aromatic Oligoamide Foldamers". J. Am. Chem. Soc. 142 (1): 257–263. doi:10.1021/jacs.9b09890. PMID 31825211. S2CID 209314136.
  5. Ohnoutek, L.; Cho, N.H.; Murphy, A.W.A.; Kim, H.; Rasadean, M.D.; Pantos, G.D.; Nam, K.T.; Valev, V.K. (2020). "Single Nanoparticle Chiroptics in a Liquid: Optical Activity in Hyper-Rayleigh Scattering from Au Helicoids". Nano Letters. 20 (8): 5792–5798. doi:10.1021/acs.nanolett.0c01659. PMC 7467767. PMID 32579377. S2CID 220060515.
  6. Ohnoutek, L.; Kim, J.Y.; Lu, J.; Olohan, B.J.; Rasadean, M.D.; Pantos, G.D.; Kotov, N.A.; Valev, V.K. (2021). "Third-harmonic Mie scattering from semiconductor nanohelices". Nature Photonics. 16 (2): 126–133. doi:10.1038/s41566-021-00916-6. S2CID 245955388.
  7. Petralli-Mallow, T.T.; Wong, T.M.; Byers, J.D.; Yee, H.I.; Hicks, J.M. (1993). "Circular dichroism spectroscopy at interfaces: a surface second harmonic generation study". J. Chem. Phys. 97 (7): 1383–1388. doi:10.1021/j100109a022.
  8. Byers, J.D.; Byers, H.I.; Hicks, J.M. (1994). "A second harmonic generation analog of optical rotatory dispersion for the study of chiral monolayers". J. Chem. Phys. 101 (7): 6233–6241. doi:10.1063/1.468378.
  9. Ohnoutek, L.; Jeong, H.-H.; Jones, R.R.; Sachs, J.; Olohan, B.J.; Rasadean, D.M.; Pantos, G.D.; Andrews, D.L.; Fischer, P.; Valev, V.K. (2021). "Optical Activity in Third-Harmonic Rayleigh Scattering: A New Route for Measuring Chirality". Laser & Photonics Reviews. 15 (11): 2100235. doi:10.1002/lpor.202100235. S2CID 240505663.
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