title: Two-step four-photon absorption.
abstract: We report a theoretical investigation of effective four-photon absorption (4PA) process and propose a two-step 4PA model of three-photon- induced excited-state absorption (ESA). Based on three-level rate-equation theory, we find an analytical result for the effective 4PA coefficient that depends on the three-photon absorption (3PA) cross-section, excited-state photophysical properties, and laser pulse duration. We present the analytical theory of the z-dependent nonlinear transmission for straightforwardly yet unambiguously evaluating the 3PA and effective 4PA coefficients simultaneously.
authors.affiliation: Jiangsu Key Laboratory on Opto-Electronic Technology and Department of Physics, Nanjing Normal University, Nanjing 210097, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Gu
authors.forename: Wei
authors.initials: W
authors.lastname: Ji
mesh_terms: D004867:Equipment Design; D007834:Lasers; D008027:Light; D015233:Models, Statistical; D055095:Optics and Photonics; D017785:Photons; D010825:Physics / Q000295:instrumentation* / Q000379:methods*; D013997:Time Factors