Power generation in coherent anti‐Stokes Raman spectroscopy with focused laser beams

Focusing effects for nonlinear power generation are explicitly discussed for coherent anti‐Stokes Raman spectroscopy (CARS). It is shown that very tight focusing only increases CARS power generation by about a factor of 4, while an extra λ−2 dependence introduced by focusing implies CARS signals scale with wavelength in the same manner as do the signals in normal spontaneous Raman scattering. Axial power generation in a gas phase medium is illustrated, and a modified plane wave approximation function is developed to analyze this behavior for loose focusing cases.