Z-scan measurement of the nonlinear response of new materials by using a high-repetition-rate femtosecond laser

Abstract

ABSTRACT Nowadays, it has become an essential task to characterize the nonlinear optical response of new materials, in order to identify suitable candidates for ultrafast processing in all-optical devices. One of the most widely-used techniques for this purpose is the Z-scan, which consists on measuring the nonlinear refractive and absorptive responses of a material by scanning the sample along the optical path of a convergent Gaussian beam. We will analyze the nonlinear response of carbon disulfide and new organic composites. In our setup, using a high-repetition rate femtosecond laser, we have included an optical chopper for managing thermal effects in order to characterize electronic nonlinearities. Keywords: Z-scan, nonlinear, femtosecond, P-scan, new materi als, transmitance, high-repetition-rate, chopper. 1. INTRODUCTION. Z-SCAN TECHNIQUE At high intensities, the refractive index of many materials can be described by the relation: n=n 0 + JI where n0 is the linear refractive index of the material, g is the nonlinear refractive index and I is the peak irradiance[1]. As it can be inferred from the equation above, the light changes the optical properties of the medium. If the energy density supplied is large enough, the nonlinear correction to the refractive index will become significant, causing the incident beam to be focused or defocused depending on the sign of J.