Researchers have observed a never-before-seen occurrence in Raman scattering, leading to new possibilities in nano-size spectroscopy.

Spectroscopy, the observation of interaction between matter and electromagnetic radiation, has different forms depending on the specific type of matter (e.g. nuclei, atoms, molecules, crystals) studied. One particularly common technique is Raman spectroscopy, which observes low-frequency movements - such as rotations and vibrations - in molecules. It is based on inelastic Raman scattering, the effect when photons originating from a laser light are scattered from a molecule. The molecule is excited to higher vibrational or rotational modes and consequently the scattered photons are detected with lower energy than the incident state. Since the energy gap between different levels of rotational or vibrational modes is specific to a given molecule, Raman spectroscopy can be used to identify compounds.

A particular case of this scattering, called Stimulated Raman scattering, which is a cubic nonlinear interaction of the incident light and photons of spontaneous Raman scattering. Researchers from Imperial College London (UK), Kazan Federal University (Russia), Harvard University (USA) and Nazarbayev University (Kazakhstan) have succeeded, for the first time, to observe a coherent amplification of the Raman scattering within titanium nitride.

The results, which were recently published in Nano Letters, will open new opportunities in the development of ultracompact (several hundreds of nanometers) Raman lasers, amplifiers and biosensors. This discovery also provides the basis for nano-size sources of laser radiation, which can be used in nano-size spectrometers. One future prospect for such small scale spectrometers is the possibility of highly sensitive biosensors which could detect even single molecules. These findings may also lead to the emergence of new field in materials science focusing on plasmonic and Raman active materials for studies of nanostructured systems.

REFERENCE:

Sergey S. Kharintsev, Anton V. Kharitonov, Semion K. Saikin, Alexander M. Alekseev, and Sergei G. Kazarian. Nonlinear Raman Effects Enhanced by Surface Plasmon Excitation in Planar Refractory Nanoantennas. Nano Letters, 17 (9), 5533–5539 2017. DOI: 10.1021/acs.nanolett.7b02252

[Article written by Dora Petra Olah, an Undergraduate student in the Department of Chemical Engineering.]