No abstract

In this work, the influence of using ion beam sputtered mixtures instead of pure materials and the impact of applied post deposition annealing to residual stress is investigated. Single layer pure films and mixtures of Nb 2 O 5 / SiO 2 as well as multilayer coatings are examined by the means of residual stress. High residual compressive stress was measured for all as-deposited samples. Pure and mixed monolayer samples were annealed at various temperatures and residual stress was determined after each annealing routine. Residual changes in optical constants, layer thickness and surface roughness upon annealing are examined to explain stress behavior. Obtained data was used to make optimization of high reflectivity structures with completely eliminated residual stress. The proposed method can be used to coat very thin substrates where flatness requirements are essential.

Spintronic metal thin films excited by femtosecond laser pulses have recently emerged as excellent broadband sources of terahertz (THz) radiation. Unfortunately, these emitters transmit a significant proportion of the incident excitation laser, which causes two issues: first, the transmitted light can interfere with measurements and so must be attenuated; second, the transmitted light is effectively wasted as it does not drive further THz generation. Here, we address both issues with the inclusion of a high-reflectivity (HR) coating made from alternating layers of SiO2 and Ta2O5. Emitters with the HR coating transmit less than 0.1% of the incident excitation pulse. Additionally, we find that the HR coating increases the peak THz signal by roughly 35%, whereas alternative attenuating elements, such as cellulose nitrate films, reduce the THz signal. To further improve the emission, we study the inclusion of an anti-reflective coating to the HR-coated emitters and find the peak THz signal is enhanced by a further 4%.

In this paper, the relation between the laser-induced damage threshold (LIDT) and the electric field intensity (EFI) distribution inside a CM is investigated experimentally. We show that it is possible to increase the LIDT values by slightly modifying the electric field of a standing wave distribution without loss of spectral and dispersion performance. Suggested CM design improvement could increase reliability and LIDT performance of both CM elements and high-power systems they are used in.

Zero incidence angle spatial filters of a compact design can be very useful, among others, for intracavity spatial filtering in high-power micro-lasers. Typically, micro-lasers, especially in high-power operation regimes, emit beams of low spatial quality due to the large aspect ratio of the laser resonator. A promising proposal for compact spatial filtering is the integration of the Photonic Crystals structures into the micro-resonator of the laser. Here, we report efficient spatial filters with desired filtering properties engineered by the inverse design. Such filters can be designed not only separately for both polarizations of the incident radiation but also simultaneously for both S and P polarizations. Moreover, we fabricate the inverse-designed structure by physical vapor deposition and highlight good correspondence of the angle-wavelength transmission map to the target one.