Coherent Raman spectro-imaging with laser frequency combs

TL;DR

This paper introduces a novel coherent anti-Stokes Raman scattering (CARS) spectro-imaging technique using two laser frequency combs, enabling rapid, high-resolution hyperspectral imaging for microscopic samples.

Contribution

It presents a new method combining laser frequency combs with CARS for fast, high-resolution spectro-imaging, overcoming previous limitations in spectral span and measurement time.

Findings

Achieved high-resolution Raman spectra in less than 15 microseconds.

Captured hyperspectral images at 50 pixels per second with high spectral and spatial resolution.

Demonstrated potential for real-time, label-free chemical imaging.

Abstract

Optical spectroscopy and imaging of microscopic samples have opened up a wide range of applications throughout the physical, chemical, and biological sciences. High chemical specificity may be achieved by directly interrogating the fundamental or low-lying vibrational energy levels of the compound molecules. Amongst the available prevailing label-free techniques, coherent Raman scattering has the distinguishing features of high spatial resolution down to 200 nm and three-dimensional sectioning. However, combining fast imaging speed and identification of multiple - and possibly unexpected- compounds remains challenging: existing high spectral resolution schemes require long measurement times to achieve broad spectral spans. Here we overcome this difficulty and introduce a novel concept of coherent anti-Stokes Raman scattering (CARS) spectro-imaging with two laser frequency combs. We illustrate the power of our technique with high resolution (4 cm-1) Raman spectra spanning more than 1200 cm-1 recorded within less than 15 microseconds. Furthermore, hyperspectral images combining high spectral (10 cm-1) and spatial (2 micrometers) resolutions are acquired at a rate of 50 pixels per second. Real-time multiplex accessing of hyperspectral images may dramatically expand the range of applications of nonlinear microscopy.