Simple Approach for 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 measurements of both CARS and spontaneous anti-Stokes Raman scattering (AS). Both CARS and AS signals can be obtained by simply switching between using two laser inputs for CARS and only one for AS. Since only the inputs differ while the measurement method remains the same, this approach is independent of the spectral sensitivity of the apparatus. We quantitatively evaluated the proposed CARS enhancement factor (CARS-EF). The CARS-EF for broadband CARS microscopy was calculated to be 250 ± 1 at a pump power of 93 mW and a broadband Stokes power of 130 mW, corresponding to ~0.2 mW/cm⁻¹. The CARS-EF serves as a universal benchmark for comparing the specifications of various CARS microscopes.