Graduate Student Kazuki Inoue and Associate Professor Masanari Okuno of the Graduate School and College of Arts and Sciences at the University of Tokyo, developed a world first novel spectroscopy method for obtaining molecular vibration spectra. The results were published in Nature Communications.
Infrared spectroscopy based on infrared absorption and Raman spectroscopy based on Raman scattering are techniques used widely to detect molecular vibrations and study molecular structure and dynamics. Raman spectroscopy in particular can be used for various samples and is widely employed in the analysis of materials and the imaging of biological samples. However, there are molecular vibrations that cannot be detected by this method. It cannot obtain all the information on molecular vibrations.
Hyper-Raman spectroscopy has been attracting attention in recent years as a technique for measuring molecular vibrations. However, hyper-Raman scattering is extremely weak, making its application difficult. The research group demonstrated for the first time in the world a new nonlinear spectroscopic method for amplifying this scattering: the "coherent anti-Stokes hyper-Raman scattering (CAHRS)" process. To amplify the process, a combined hyper-Raman and coherent Raman process was used to detect the signal.
The CAHRS process was theoretically proposed approximately 40 years ago; however, this is the first time it has been experimentally demonstrated. Utilizing their knowledge of hyper-Raman spectroscopy, the researchers constructed a spectrometer to realize CAHRS spectroscopy. As the CAHRS process is based on fifth-order nonlinear optical effects, signals from lower-order optical effects may mix.
The research group performed spectroscopic experiments from various perspectives and demonstrated that the signal detected in this study was indeed a true CAHRS signal. Moreover, they measured a para-solution and benzene that were used as test samples. The measurements demonstrate that CAHRS spectroscopy can detect a signal with a much higher signal-to-noise ratio much faster (one-tenth of the time) compared to conventional spontaneous hyper-Raman spectroscopy.
This research has made it possible to amplify weak signals and detect hyper-Raman scattering signals in a short time. Further, measurements that were previously considered impossible with hyper-Raman spectroscopy are now possible. The method is expected to contribute to innovations in measurement techniques not only in basic physical chemistry but also in analytical chemistry.
Journal Information
Publication: Nature Communications
Title: Coherent Anti-Stokes Hyper-Raman Spectroscopy
DOI: 10.1038/s41467-024-55507-0
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