Epsilon-near-zero-materials and their unique properties are key to successful integration and miniaturization of optical components. Novel concepts, which promise significant progress in this field of research, such as optical switches and thin film electro-optical modulators, are possible, when the electrical and optical properties of ENZ-materials are carefully exploited. To achieve a greater understanding of these properties, this contribution investigates the electrical conductivity, optical transmittance as well as losses of thin indium tin oxide films and links them to their LIDT at various ultrashort pulse durations.
Third harmonic generation (THG) in dielectric films with femtosecond laser pulses is used to study properties of dielectric thin films and stacks thereof below and above the 1-on-1 laser damage threshold. Deviations from the ideal cubic relationship between third-harmonic signal and incident fundamental fluence are a result of several fundamental processes. Their relative contributions are assessed by comparing results from LIDT and conversion efficiency measurements as well as beam profile and pump-probe studies.
The exploitation of nonlinear effects in multi-layer thin films allows for optics with novel functions, such as all- optical
switching and frequency conversion. In this contribution, an improved interferometric setup for the measurement of the
nonlinear refractive index in dielectric substrates and deposited single layers is presented. The setup is based on the wave
front deformation caused by the self-focusing in the measured samples. Additionally, measurement results for a highly
nonlinear material, indium-tin-oxide (ITO) are presented with respect to the materials power handling capabilities and
compared to values from other materials.
We have studied laser induced material modification in a frequency tripling mirror (FTM) consisting of alternating hafnia and silica layers. The third-harmonic signal generated by a train of femtosecond laser pulses (791 nm, 55 fs, 110 MHz) drops over time until it reaches about 20% of the initial value. From the observed changes in reflection and transmission of the mirror a refractive index change of 0.07 was estimated, which occurs in the layer with the highest field enhancement. This index change triggers a drop in the field enhancement, which reduces the efficiency of nonlinear optical processes. The estimated value of ▵n allowed us to explain the 80% reduction in conversion efficiency and as well as an observed decrease in two-photon absorption.
Based on the z-scan method, an interferometric set-up for measuring the optical Kerr-effect was engineered and optimized. Utilizing a Mach-Zehnder configuration, the wave front deformation caused by the Kerr induced selffocusing is monitored. Fitting this deformation to a theoretical approach basing on a beam propagation model, the nonlinear refractive index is obtained. The procedure can be applied to measure the nonlinear refractive index of both, the substrate material as well as the deposited dielectric layer on top of the substrate. The nonlinear refractive index of a layer specially deposited for this purpose as well as for several substrate materials was measured and the results presented.