| Abstract [eng] |
The main goal of this research was to examine the possibility of applying ion beam sputtering method for the production of multilayer mirrors for the mid-IR spectral range. The work mainly focused on low GDD and dispersive mirrors since availability of such components currently is very limited. In the first part of the research, monolayers of Ta2O5, Nb2O5, TiO2, SiO2, Si and Si/SiO2 mixtures were deposited. Refractive indices, extinction coefficients and mechanical stresses of the materials were examined. Modelled optical features of the materials in the 1–5 µm range revealed that all oxide materials have absorption losses in the 2.7–4 µm range. The nature of the losses was attributed to water presence in the layers for Ta2O5, Nb2O5, TiO2 and SiO2. It was found that by ex-situ annealing at high temperatures (> 600 °C), SiO2 absorption can be removed in this range. Si and Si/SiO2 mixture layers incurred the lowest losses in this spectral range and yet exhibited the highest refractive indices (Si n=3.75@ 3000 nm; Si/SiO2 2 sccm O2  n =3.36@ 3000 nm; TiO2  n=2.28@ 3000 nm), making them the suitable option for multilayers. All materials showed compressive stress as deposited, which was decreased by increasing annealing temperature. Broadband highly reflecting multilayer was successfully deposited using the Si and SiO2 material pair. After ex–situ annealing, the mirror yielded > 99.9% average reflectivity in the 1750–3200 nm wavelength range and its low GDD performance (<30 fs2@ 1800–2800 nm) was confirmed by interferometric measurements. Finally, a dispersive mirror for pulse compression in the 1–5 µm range was deposited using the Si and SiO2 material pair. The mirror exhibited an average reflectivity of 98.5% in the 2150–3750 nm range. This multilayer had a specially designed GDD curve (from -300 fs2@ 2150 nm to +300 fs2@ 3700 nm) and was intended for pulse compression in combination with CaF2 bulk material. Real-life test in a pulse compression setup was performed and 30 fs initial spectrally broadened pulse, centered at 3.2 µm, was successfully compressed to sub-2 optical cycle pulse (18.9 fs). |
