Raman Spectroscopy Gets Major Speed Upgrade

Researchers at the University of Tokyo have increased the measurement rate of Raman spectroscopy by 100-fold. Since the measurement rate of the technique has been a major limitation, the improvement is expected to aid advancements in multiple fields relying on the identification of molecules and cells, such as biomedical diagnostics and material analytics.

As a mode of identification for cells and molecules, Raman spectroscopy is widely used, but it’s limited in its ability to keep up with the speed of changes in certain chemical and physical reactions due to the low scattering cross section.

Over the last decade, various broadband-coherent Raman scattering spectroscopy techniques have been developed to address the limitation, achieving a measurement of 500 kSpectra/s (kilospectra per second).

A Raman spectroscopy technique developed at the University of Tokyo combines coherent Raman spectroscopy, an ultrashort pulse laser, and time-stretch technology to achieve a 100-fold increase in measurement rate compared to previous methods. Courtesy of the University of Tokyo.

In order to further improve the measurement rate, the team built a system from scratch, leveraging a mode-locked ytterbium laser system developed by Takuro Ideguchi and his team at the Institute for Photon Science and Technology at the University of Tokyo.

In building the system, the team combined coherent Raman spectroscopy — a version of Raman spectroscopy that produces stronger signals than the conventional, spontaneous Raman spectroscopy— with their previously developed specifically designed ultrashort pulse laser and time-stretch technology using optical fibers.

The developed system provides a 50 MSpectra/s (megaspectra per second) measurement rate, a 100-fold increase compared to the previous fastest rate of 500 kSpectra/s. The system enables highly efficient Raman scattering with an ultrashort femtosecond pulse and sensitive time-stretch detection with picosecond probe pulse at a high repetition of the laser.

As a proof-of-concept, the team measured broadband coherent Stokes Raman scattering spectra of organic compounds covering the molecular fingerprint region from 200 to 1200 cm^-1.

“We aim to apply our spectrometer to microscopy, enabling the capture of 2D or 3D images with Raman scattering spectra,” Ideguchi said. “Additionally, we envision its use in flow cytometry by combining this technology with microfluidics. These systems will enable high-throughput, label-free chemical imaging and spectroscopy of biomolecules in cells or tissues.”

According to the researchers, the high-speed broadband vibrational spectroscopy technique holds promise for unprecedented measurements of sub-microsecond dynamics of irreversible phenomena and extremely high throughput measurements.

The research was published in Ultrafast Science (www.doi.org/10.34133/ultrafastscience.0076).