STUDY ON THE REFRACTIVE NON-LINEARITY OF THREE-PHOTON ABSORBING MEDIA WITH THE Z-SCAN TECHNIQUE

Abstract

By using the Gaussian beam Z-scan technique with the zeroth-order Hankel transform method, a theoretical study on the refractive non-linearity of the three-photon absorbing media is presented in this work. The normalized transmittance expression of the closed-aperture Z-scan is derived for the medium with three-photon absorption, third- and fifth-order non-linear refractions. At low irradiance, an analytical approximation of the normalized transmittance, which is helpful for unambiguously extracting the simultaneous third- and fifth-order non-linear refractive indexes, and three-photon absorption coefficient, is obtained. By using this method with 80 fs laser pulses, the non-linear refractive properties of a three-photon absorbing dye solution is studied experimentally, which shows a larger fifth-order refractive non-linearity with respect to the third-order one due to the three-photon absorption resonant enhancement.