With the advent of lasers, Raman spectroscopy has been used as a valuable tool in vibrational spectroscopy for investigating the properties of matter. When the scattering is inelastic, with the transfer of energy between the photon and molecule, either the molecule gains energy from the photon, leading to the Stokes scattering or the molecule loses energy to the photon, leading to the anti-stokes scattering. Quantum mechanically Stokes and Anti-Stokes are equally likely processes. However, Anti-Stokes scattering requires vibration level to be populated. This population is directly dependent on energy in the given vibration mode. In equilibrium, this energy comes from the temperature but during the reaction, the vibration population can be a direct consequence of the previous reaction. For this reason, an asymmetry between Stokes and anti-Stokes scattering potentially provides valuable information about the (bio)chemical reaction mechanism, especially if it can be recorded with high temporal resolution.
The anti-stokes to stokes intensity ratio as a function of temperatures is,
(1)
Where , is the laser frequency, T is the sample temperature, k is the Boltzmann constant, Ias, Is are the anti-stokes and stokes intensities.[1]
We are proposing an imaging set up, based on simultaneous measurement of Stokes and anti-Stokes Raman scattering. Such set up should deliver contrast related to specific underlying reactions and enhance resistance to fluorescence background that is notorious in Raman microscopy.