Two-photon absorption coefficient determination with a differential F-scan technique

In this paper we present a modification to the recently proposed transmission F-scan technique, the differential F-scan technique. In differential F-scan technique the programmed focal distance in the electronic-tunable lens oscillates, allowing the light detector of the setup to record a signal proportional to the derivative of the signal recorded with an F-scan. As for the differential Z-scan a background-free signal is obtained, but also the optical setup is simplified and the available laser power is double. We also present and validate a new fitting-procedure protocol that increments the accuracy of the technique. Finally, we show that fitting a signal from differential F-scan or the derivate of the signal of transmission F-scan is more accurate than simply fitting the signal from F-scan directly. Results from two-photon absorption at 790 nm of CdS, ZeSe and CdSe are presented.