Laser and optical technologies

This group deals for a long time with advanced approaches and applications focused on various areas of applied optics. The main focus has been on proposals, analyses, designs and production of non-standard optical elements and systems (both imaging and non-imaging), e.g., optical systems of fluorescent detectors determined for cosmic rays research. Optical technologies (innovation of classical technologies for processing of hard and very hard materials, especially of glass) – rough and fine grinding, polishing, novel approach to surface glass processing using the subaperture method have been developed and employed. Related development has been performed in the area of optical layers and the methods of their analysis. 
The ability to manufacture ultra-lightweight mirror surfaces of large dimensions is a group specialty employed for instance in the Pierre Auger Observatory (PAO) located in Argentina (see, e.g., Nucl. Instrum. Meth. Phys. Res. Sec. A 2010, 620, 227). The success of PAO resulted in involvement in the international collaboration CTA – Cherenkov Telescope Array – where the subgroup develops measurement systems and methods for quality evaluation of production and service wear of mirror samples, supplied by different potential producers and intended for using in optical telescopes as detectors of cosmic rays (Astropart. Phys. 2013, 43, 3). Since both these projects rely on observation of secondary phenomena in the atmosphere, the fluorescence properties of the atmosphere have been of particular interest (Astropart. Phys. 2013, 42, 90). The need for long-time observation of the cloud-coverage and optical background of the night sky resulted in the design and construction of a specialized autonomous all-sky camera. The cameras have been in the possible locations of CTA observatories (four cameras are already installed in the USA and Argentina, one in Chile, Namibia, Canary Islands and Mexico), and are also included in Pierre Auger Observatory in Argentina as a part of observatory control system.
The subgroup contributes also to other tasks applicable in the industry (e.g., device controlling in real-time color markings of coil springs produced at production line for automotive industry, or research and optimization of optical systems for yarn quality management during its production). The involvement of the team in Pierre Auger and CTA collaborations resulted in contribution to more than 40 publications in Web-of-Science-registered journals. In these collaborations, the team closely cooperates with the Astroparticle physics group of the Institute of Physics of AS CR. 

In the area of material properties, the group was focused primarily on the experimental analysis of mechanical and tribological properties at small scales using the state of the art equipment and methods. In most cases the work was driven by both the scientific curiosity and the technological interest. Various types of materials were tested including thin films and coatings (ceramics, metals, nanocomposites) (Surf. Coat. Technol. 2011, 205, 3372, Surf. Coat. Technol. 2011, 205, 4052, Surf. Coat. Technol. 2012, 206, 3580), plasma sprayed coatings (Ceramics Int. 2010, 36, 2155), single crystals (Appl. Phys. Lett. 2014, 105, 082906) and other bulks. Depth sensing nanoindentation and scratch tests were performed at room temperature and at elevated temperatures up to 500 °C. It should be noted that this subgroup is the only one in the Czech Republic experienced in the high temperature measurements at nano/micro scale and belongs to a limited number of groups worldwide capable to explore nanomechanical properties at elevated temperatures. In case of thin films and plasma sprayed coatings the mechanical characteristics were correlated with the structure and with the parameters of the deposition process providing a comprehensive description of the studied material. Besides, the temperature stability of the films’ structure and mechanical properties was explored. Especially the potential of hard SiCN (Surf. Coat. Technol. 2014, 240, 76) and superhard B4C films were systematically studied. The research works dealing with thin films and coatings were mainly performed under the cooperation with the Institute for Problems of Materials Science, Academy of Sciences of Ukraine. In cooperation with the Virginia Polytechnic Institute and State University, a modified nonisothermal nanoindentation method was developed to directly detect the negative stiffness of ferroelectric material at its Curie point and to quantify the negative stiffness without the need for embedding it into a matrix. The feasibility of this in-situ method was demonstrated on the triglycine sulfate single crystal.

In the area of laser technologies, the overlap welding of thin stainless steel sheets was performed by means of the pulsed Nd:YAG laser system with variable laser parameters, that influence was investigated on the samples cross-sections by laser scanning microscopy. Numerical model of the pulsed welding was created by software SYSWELD with the goal to estimate the amount of the absorbed energy (Metallurg. Mater. Trans. B 2010, 41, 1108; Metallurg. Mater. Trans. B 2014, 45, 1116). The possibility of the on-line monitoring of the welding process was investigated both on our own Nd:YAG pulsed laser system and on industrial continual CO2 laser in LAMBRO 92 a.s. facility. UV – spectrometer or UV – photodiode data were collected and evaluated by the developed software LWM – Laser welding monitor (J. Mater Eng. Perf. 2012, 21, 764). Numerical model of the overlapped laser surface melting was created to demonstrate the influence of delay between the following spot application, spot axis stand-off and the processing speed on the resulting microstructure in the remelted region. Real samples were processed on high power diode laser in MATEX PM Facility in Plzeň and surface modification was evaluated by contact stylus profilometry. Besides these main tasks, laser liquid-assisted scribing of silicon, indirect backside glass marking, and laser interaction with nano-particles were performed. Also the research of propagation and shaping of extremely powerful light beams (in collaboration with ELI project and industrial environment) has been pursued.

Latest publications of the group

  • Azamat, DV; Badalyan, AG; Baranov, PG; Trepakov, VA; Hrabovsky, M; Jastrabik, L; Dejneka, A: EPR and ENDOR in manganese doped SrTiO3: Electric quadrupole interaction and local disorder, J. Appl. Phys. 124 (12) 124101 (2018).
  • Simurka, L; Ctvrtlik, R; Tomastik, J; Bektas, G; Svoboda, J; Bange, K: Mechanical and optical properties of SiO2 thin films deposited on glass, Chem. Pap. 72 (9) , 2143 - 2151 (2018).
  • Kmentova, H; Kment, S; Hubicka, Z; Remes, Z; Olejnicek, J; Cada, M; Krysa, J; Zboril, R: Thermal sulfidation of alpha-Fe2O3 hematite to FeS2 pyrite thin electrodes: Correlation between surface morphology and photoelectrochemical functionality, Catal. Today 313 , 224 - 230 (2018).
  • Tomastik, J; Ctvrtlik, R; Ingr, T; Manak, J; Opletalova, A: Effect of Nitrogen Doping and Temperature on Mechanical Durability of Silicon Carbide Thin Films, Sci Rep 8 10428 (2018).
  • Simurka, L; Ctvrtlik, R; Roch, T; Turutoglu, T; Erkan, S; Tomastik, J; Bange, K: Effect of deposition conditions on physical properties of sputtered silicon oxynitride thin films on float glass, Int. J. Appl. Glass Sci. 9 (3) , 403 - 412 (2018).

Latest publications of the Pierre Auger Collaboration (including JLO members)

  • Aab, A et al. (Chytka, L.; Horvath, P.; Hrabovsky, M.; Michal, S.; Nozka, L.; Supik, J.): Measurement of the average shape of longitudinal profiles of cosmic-ray air showers at the Pierre Auger Observatory, J. Cosmol. Astropart. Phys. (3) 18 (2019).
  • Aab, A et al. (Chytka, L.; Horvath, P.; Hrabovsky, M.; Michal, S.; Nozka, L.; Supik, J.): Large-scale Cosmic-Ray Anisotropies above 4 EeV Measured by the Pierre Auger Observatory, Astrophys. J. 868 (1) 4 (2018).
  • Aab, A et al. (Chytka, L.; Horvath, P.; Hrabovsky, M.; Michal, S.; Nozka, L.; Supik, J.): Observation of inclined EeV air showers with the radio detector of the Pierre Auger Observatory, J. Cosmol. Astropart. Phys. (10) 26 (2018).
  • Aab, A et al. (Horvath, P.; Hrabovsky, M.; Nozka, H.): Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory (vol 4, 038, 2017), J. Cosmol. Astropart. Phys. (3) E02 (2018).
  • Aab, A et al. (Horvath, P.; Hrabovsky, M.; Michal, S.; Nozka, L.; Supik, J.): An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources, Astrophys. J. Lett. 853 (2) L29 (2018).