Complementary Si/SiO2 dispersive mirrors for 2-4†µm spectral range.

Complementary pair of dispersive multilayers operating in the 2-4 µm spectral range were designed and produced for the first time. The mirrors comprise layers of Si and SiO2 thin-film materials. The pair exhibits unparalleled reflectance exceeding 99.7% and provides a group delay dispersion of (-200) fs2. The mirrors can be used in Cr:ZnS/Cr:ZnSe femtosecond lasers and amplifiers.

Synthesis, fabrication and characterization of a highly-dispersive mirrors for the 2 µm spectral range.

We report a challenging design, fabrication and post-production characterization problem of a dispersive mirror supporting the spectral range from 2000 nm to 2200 nm and providing a group delay dispersion of -1000 fs2. The absolute reflectance in the working range is over 99.95%. The reported mirror is a critical element for Tm and Ho based lasers and paves the way for the development of ultrafast 2 µm lasers with sub-100 fs pulse duration.

Broadband beamsplitter for high intensity laser applications in the infra-red spectral range.

We report on design, production and characterization of an extremely broadband multilayer beamsplitter, covering wavelength range from 0.67 - 2.6 µm. The group delay dispersion has small oscillations in the above mentioned working range. We used a new algorithm with floating constants allowing us to obtain a smooth and near constant GDD. The optical element based on the beamsplitter is used for dividing a low-energy super-octave spectrum into several sub-spectral regions which are later amplified and coherently combined.

Stress compensation with antireflection coatings for ultrafast laser applications: from theory to practice.

Each complicated coating, in particular, a dispersive mirror consists of dozens of layers. Thin films layers have mechanical stresses. After summing up stresses from all layers, the resulting stress is high enough to bend even a relatively thick substrate. To avoid this effect we suggest depositing an antireflection coating (AR) at the back-side of the substrate which together with suppression of unwanted reflections from the back side will also compensate this stress. We demonstrate unique, extremely thick and sophisticated AR coating consisting of 71 layers with the total physical thickness of 7.5 µm. This AR coating completely compensates stress from the dispersive mirror coated on the front side and minimizes unwanted reflections.