Molecular symmetries by coherent Raman scattering

Abstract

Obtaining information on the matter organization on the micrometer scale still remains a challenge in physics, chemistry or biology. Non-linear vibrational processes such as Coherent Anti-Stokes Raman Scattering (CARS) are powerful tools for 3D imaging of chemical properties without sample preparation. The CARS process is a stimulated Raman process based on the interaction of 2 photons, called pump at frequency ωp, and Stokes at frequency ωs. When the frequency difference corresponds to a vibrational resonance (Ωr = ωp−ωs), an anti-Stokes photon is generated at the frequency ωas = 2 ωp-ωs. In this case, the measured intensity specifically reveals the presence of the chemical bonds, much more efficiently than the spontaneous Raman, thus enabling rapid imaging.