The Hyper Raman Effect: A New Method for Vibrational Mode Classification

Raman spectroscopy has been used by scientists for years. One of the significant advancements in this field is hyper Raman spectroscopy. Such spectroscopy provides information on molecules that is not possible with traditional Raman spectroscopy.

What is Raman spectroscopy? Raman spectroscopy is a type of vibrational spectroscopy that relies on Raman scattering to deduce the vibrational, rotational, and other low-frequency modes on different molecules. The spectrometer can back out the chemical structure of the molecule being analyzed after isolating these modes. Raman scattering is a form of inelastic light scattering. This type of inelastic scattering occurs because the incident photons (produced by a monochromatic laser source) become scattered into photons with a different frequency. This change in frequency causes a measurable difference in the energy and wavelength between the detectable photon and the incident photon. This is also known as the Raman effect. Raman spectroscopy system has become a valuable tool across many areas of science. There are many different molecules and materials that can be analyzed with Raman spectroscopy: almost all of these molecules and materials have a crystalline nature because the lattices provide a much better light from scattering environment.


How does hyper Raman spectroscopy differ from standard Raman spectroscopy?

Hyper Raman spectroscopy is a modified version of Raman spectroscopy. Such type of spectroscopy system implies that the scattered light is at frequencies which are lower than twice the frequency of the incident light. This approach means that two incident photons become converted into a single photon of scattered light and a photon. The weak signal produced by hyper Raman system can be used to provide vibrational information on some silent modes which are suppressed by conventional Raman system. There have been a couple of interesting developments which are based on hyper Raman system and, accordingly, on Raman probes such as:

  • surface enhancement through plasmons

(There is dedicated Raman technique to this type of analysis, known as surface-enhanced Raman spectroscopy (SERS). This is being applied to hyper Raman spectroscopy through plasmonic substrates in order to enhance the weak hyper Raman signal).

  • the combination of resonance Raman and hyper Raman spectroscopy systems

(Resonance hyper Raman spectroscopy is seen to be a nonlinear Raman method, and as a result, is more sensitive because the amount of energy emitted is lower than the incident energy.)

Optromix provides fiber optic Raman probes, which are produced for multi-wave excitations in the range 690-785 nm, e.g. @785nm – “Fingerprint” spectral range with fluorescence reduction, and @690nm – “High wavenumber” spectral range for conventional Raman spectrometers. Raman fiber optic probes are miniaturized without compromising their performance, which is enabled by the technology of direct deposition of the dielectric filters at the fiber end faces. It results in a small, cost-effective Raman probe for endoscopic and other applications.

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