Two-photon absorption with vector Gaussian beams

In this study, we present an analytical model for nonlinear absorption processes utilizing vectorial Gaussian beams within the weak nonlinearity regime. We have developed an expression for normalized transmittance, encompassing both linear and second-order nonlinear absorption, while incorporating the axial field component of tightly focused beams. This model, contextualized within the Z-scan technique framework, enables precise characterization of nonlinear absorption coefficients. Our simulations examine the effects of various polarization states and beam focusing characteristics on nonlinear absorption. The results unveil nuanced differences in nonlinear absorption among linearly polarized, circularly polarized, and unpolarized light. Notably, increasing the beam divergence angle results in broader transmittance curves, while the nonlinear absorption magnitude remains relatively stable. These findings underscore the significance of considering the full vectorial nature of tightly focused beams in nonlinear optics. Our model elucidates the intricate relationship between beam properties and nonlinear responses, with implications for applications such as nonlinear microscopy, optical limiting, and advanced photonic device development.