Design and assembly of an open aperture Z-scan setup based on a high-power femtosecond oscillator

Abstract

The Z-Scan technique has become a standard method to characterize higher order nonlinearities such as two-photon absorption, which have found applications from 3D nanolithography to high-resolution 3D microscopy. However, usually Z-scan is performed at one single wavelength, providing only limited information on the spectral characteristic of compounds like photoinitiators and fuorescent dyes. The aim of this thesis was to design a fully automated Z-Scan to characterize the nonlinear absorption properties of different compounds. This novel setup was based on a tunable high-power femtosecond oscillator, allowing scans from 690-1040 nanometers. A beam profiling method was implemented to efficiently extract the parameters of the focused beam. For the Z-Scan Rhodamine B was selected as reference material, since its cross section is well known in literature. Compared to conventional amplified systems oscillator based Z-Scans can lead to thermal effects due to the high average power, which compromise the results. These effects were reduced by installing a beam chopper and adapting the software accordingly. The modifications allowed successful Z-Scan measurements which were comparable to Z-Scans using amplified systems. Therefore, the oscillator based Z-Scan shows promise as a tool for spectral analysis of two-photon absorption.