Method for an accurate measurement of nonlinear refractive index in the case of high-repetition-rate femtosecond laser pulses

Abstract

In this report, we propose a new method for measuring the nonlinear refractive index in liquid and glass samples using femtosecond (fs)-laser pulses with high pulse repetition rates. This method is based on solving the heat equation to derive an expression for the normalized transmittance of closed-aperture Z-scan measurements as a function of the accumulative thermal lens induced by a high-repetition-rate fs laser pulse. To validate this method, the nonlinear refractive indices of acetone as a liquid and soda-lime as a glass material have been measured using a 100 fs pulse duration, 80 MHz repetition rate, and 800 nm wavelength. The extracted nonlinear refractive index is in a good agreement with the reported one using 1 kHz repetition rate fs laser pulses.