Simple Approach to Determine the Universal and Quantitative Enhancement Factor in Coherent Anti-Stokes Raman Scattering (CARS) Microscopy

We propose a simple approach to determine the coherent anti-Stokes Raman scattering (CARS) enhancement factor (EF), based on the measurement of both CARS and spontaneous anti-Stokes Raman scattering (AS). Both CARS and AS signals can be obtained by simply switching between two laser inputs for CARS and only one input for AS. As only the inputs differ while the measurement method remains the same, this approach is independent of the spectral sensitivity of the apparatus. We quantitatively determined CARS-EF using cyclohexane and toluene, both of which are transparent solvents. The CARS-EF for ultrabroadband multiplex CARS microscopy was calculated to be 467 ± 10, at a pump power of 38 mW and broadband Stokes power of 72 mW, corresponding to ~0.11 mW/cm⁻¹. The CARS-EF serves as a universal benchmark for comparing the specifications of various CARS microscopes.