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Analytical Chemistry

Speeding Up CARS

Spectroscopy: Method acquires a speedy 24,000 CARS spectra per second

by Celia Henry Arnaud
February 26, 2016 | APPEARED IN VOLUME 94, ISSUE 8

The spectroscopy technique known as coherent anti-Stokes Raman scattering (CARS) is used for label-free imaging in many biomedical applications. One drawback of CARS is slow spectral acquisition, which can produce fuzzy images. A team led by Keisuke Goda and Takuro Ideguchi of the University of Tokyo has developed an instrument that speeds up CARS scan rates by a factor of more than of 20 compared with previous methods (Sci. Rep. 2016, DOI: 10.1038/srep21036). In Fourier transform CARS, a train of laser pulses delayed with respect to one another excites and probes molecular vibrations. By varying the time delay, the CARS spectrum can be encoded in an interferogram that can be decoded with a Fourier transform. The researchers speed up their data acquisition by incorporating into a conventional FT-CARS instrument a system that allows them to change the path length and thus the time delay by rapidly changing the angle of one of the mirrors. In a demonstration, they used the method to monitor the mixing dynamics of toluene and benzene with resolution of 10 cm−1 over the 200- to 1,500-cm−1 spectral region at a scan rate of 24,000 spectra per second. Previous methods acquire spectra at a rate of about 1,000 spectra per second.

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