
Hyper–Rayleigh scattering optical activity ( ), a form of chiroptical harmonic scattering, is a
nonlinear optical
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typicall ...
physical effect whereby chiral scatterers (such as nanoparticles or molecules) convert
light
Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
(or other
electromagnetic radiation
In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength ...
) to higher frequencies via
harmonic generation
Harmonic generation (HG, also called multiple harmonic generation) is a nonlinear optical process in which n photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with n times the energy of t ...
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
Rayleigh scattering ( ) is the scattering or deflection of light, or other electromagnetic radiation, by particles with a size much smaller than the wavelength of the radiation. For light frequencies well below the resonance frequency of the scat ...
. "
Optical activity
Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
" refers to any changes in light properties (such as intensity or polarization) that are due to
chirality
Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable fro ...
.
History
The effect was theoretically predicted in 1979, 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.
[
] The team investigated the hyper Rayleigh scattering (at the
second harmonic generation
Second-harmonic generation (SHG), also known as frequency doubling, is the lowest-order wave-wave nonlinear interaction that occurs in various systems, including optical, radio, atmospheric, and magnetohydrodynamic systems. As a prototype behav ...
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,
plasmonic metal nanoparticles and semiconductor nanoparticles.
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 or second harmonic generation optical rotation. Moreover, HRS OA is a
parametric process: the initial and final quantum mechanical states of the excited electron are the same. Because the excitation proceeds via
virtual state
In quantum physics, a virtual state is a very short-lived, unobservable quantum state.
In many quantum processes a virtual state is an intermediate state, sometimes described as "imaginary" in a multi-step process that mediates otherwise forb ...
s, there is no restriction on the frequency of incident light. By contrast, other nonlinear scattering effects, such as
two-photon circular dichroism
Two-photon circular dichroism (TPCD), the nonlinear counterpart of Circular dichroism, electronic circular dichroism (ECD), is defined as the differences between the Two-photon absorption, two-photon absorption (TPA) cross-sections obtained using ...
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,
the effect was replicated in organic molecules, specifically aromatic oligoamide foldamers.
[
]
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 silver nanohelices.
[
]
See also
*
Linear dichroism
*
Magnetic circular dichroism
Magnetic circular dichroism (MCD) is the differential absorption of left and right circularly polarized (LCP and RCP) light, induced in a sample by a strong magnetic field oriented parallel to the direction of light propagation. MCD measurements ...
*
Optical activity
Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
*
Optical isomerism
In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...
*
Optical rotation
Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
*
Optical rotatory dispersion
In optics, optical rotatory dispersion is the variation of the specific rotation of a medium with respect to the wavelength of light. Usually described by German physicist Paul Drude's empirical relation:
alpha\lambda^T=\sum_^\infty\frac
wh ...
*
Protein circular dichroism data bank
*
Raman optical activity
Raman optical activity (ROA) is a vibrational spectroscopic technique that is reliant on the difference in intensity of Raman scattered right and left circularly polarised light due to molecular chirality.
History of Raman optical activity
The ...
(ROA)
*
Two-photon circular dichroism
Two-photon circular dichroism (TPCD), the nonlinear counterpart of Circular dichroism, electronic circular dichroism (ECD), is defined as the differences between the Two-photon absorption, two-photon absorption (TPA) cross-sections obtained using ...
*
Vibrational circular dichroism Vibrational circular dichroism (VCD) is a spectroscopic technique which detects differences in attenuation of left and right circularly polarized light passing through a sample. It is the extension of circular dichroism spectroscopy into the infrar ...
References
External links
New physical effect demonstrated by University of Bath scientists after a 40 year search official press release by the
University of Bath
The University of Bath is a public research university in Bath, England. Bath received its royal charter in 1966 as Bath University of Technology, along with a number of other institutions following the Robbins Report. Like the University ...
.
Bath University has something to twist and shout about after 40-year search by the
EPSRC
The Engineering and Physical Sciences Research Council (EPSRC) is a British Research Council that provides government funding for grants to undertake research and postgraduate degrees in engineering and the physical sciences, mainly to univers ...
.
Hyper-Rayleigh scattering published in the scientific journal ''
Nature Photonics
''Nature Photonics'' is a peer-reviewed scientific journal published by the Nature Publishing Group. The editor-in-chief is Oliver Graydon. The journal covers research related to optoelectronics, laser science, imaging, communications, and other as ...
''.
{{DEFAULTSORT:Hyper-Rayleigh scattering
Nonlinear optics
Scattering, absorption and radiative transfer (optics)
Chirality