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Frequency tripling mirrors offer a promising alternative to complicated cas- caded arrangements for third harmonic generation. By incorporating optimised dielectric layers, we have achieved a remarkable conversion efficiency of 3.5 %. We will give a deep insight into FTMs and discuss applications. © 2024 The Author(s)

Starting from C 6 H 4 (PCl 2 ) 2 and the TMS-substituted ylide (TMS) 2 C=PR 3 (TMS=trimethylsilyl, R=p-tolyl), the phosphonium-substituted diphosphaindenylide PPI was prepared in two steps. CASSCF calculations as well as the reactivity toward diphenyl acetylene suggest a notable biradical character in PPI. Reaction with [Cr(CO) 3 (MeCN) 3 ] affords the complex [Cr(CO) 3 (η 5 -PPI)] (5). This complex was employed to explore the ligand properties of PPI, which demonstrates considerable potential through the combination of strong metal-ligand interactions and the possibility of a pronounced indenyl effect., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Third harmonic generation (THG) from dielectric layers is investigated. By forming a thin gradient of HfO 2 with continuously increasing thickness, we are able to study this process in detail. This technique allows us to elucidate the influence of the substrate and to quantify the layered materials third χ (3) (3ω: ω, ω, ω) and even fifth order χ (5) (3ω: ω, ω, ω, ω, - ω) nonlinear susceptibility at the fundamental wavelength of 1030 nm. This is to the best of our knowledge the first measurement of the fifth order nonlinear susceptibility in thin dielectric layers.

A large range of laser-matter applications employ ultrashort pulses and high laser intensity. Such processes can lead to unrequired X-ray generation, which represents a hazardous radiation factor even for common laboratory research-grade laser systems. We present here an analysis of the radiation dose rate and X-ray spectrum emitted during ablation of a rotating copper cylinder with respect to several laser parameters. The results show that focused sub-picosecond pulses with intensity above 10 13  W/cm 2 can exceed the annual irradiation limit even in one hour, requiring appropriate shielding for the safety of the researchers.