Digital processing of shadowgraph images taking into account the diffraction of light at a shock front

The aim of the study is to determine the shock wave position in experimental shadowgraph images and to evaluate the accuracy by digital image processing. The experimental images were obtained with the shock tube with a rectangular channel. The shadowgraph optical system formed a parallel light beam. It passed through the plane-parallel quartz glasses of the shock tube test section. The process synchronization system at the facility allows registering the shadowgraph images of unsteady flows with shock waves with a high-speed camera or with a single frame camera. The obtained spatial intensity profiles were used to determine the coordinates of gas-dynamic discontinuities at different stages of the flow evolution. shadowgraph patterns were analysed taking into account diffraction at the shock front in case of a laser light source.

Radiation hardening and optical properties of materials based on SiO2

Preliminary studies have shown that the optical absorption spectra of radiation-colored glasses correspond to the spectral behavior of the scattering losses of an optically inhomogeneous medium. The reasons for the same optical changes in glasses of different compositions are the radiation-induced electric charge separation in the structurally nano-inhomogeneous glass volume, polarization and formation of nanometer optical inhomogeneities. The authors of this work prove that the radiation changes in the mechanical and optical properties of silicate glasses are of the same nature. The performed estimates indicate that the electric charge separation in the glasses occurs up to absorbed doses of about 1 MGy. The local electric charge separation due to the appearance of Coulomb forces leads to radiation hardening of the glasses. The estimated Coulomb hardening of the quartz glasses was ~ 107 Pa. The theoretical results were experimentally confirmed by measuring the mechanical properties of the glasses under high intensity proton irradiation as well as by testing the mechanical strength of a composite material based on quartz glass. Under proton irradiation with a dose rate of 5×103 Gy/s (energy of 8 MeV) up to threshold doses of ~ (1 – 5) ×106 Gy in the KU-1 quartz glasses, the decrement of acoustic vibrations decreased due to Coulomb hardening. After gamma irradiation with 1.34×105 Gy, the tensile strength of the composite material based on quartz glass increased by up to 20 MPa. This value is in the range of estimates of Coulomb hardening of quartz glasses. It is also shown that ionizing radiation does not affect the elastic modulus of materials based on SiO2.

Ammonia Room Temperature Gas Sensor Using Different TiO2 Nano-structure

In this study, TiO2 Nano-structure were synthesized by three different processes including nanowires, nanoparticles and thin- films. The morphology and crystal structure of the three different TiO2 structures deposited on quartz glasses were characterized by XRD, SEM and FTIR. It has been found that nanowires and nanoparticles showed only the anatase phase while the thin-film exhibited both anatase and rutile phases. The three TiO2 Nano-structures were then used to fabricate gas sensors for ammonia (NH3) detection at different concentrations and various conditions. The samples fabricated with thin-film TiO2 towards 50 ppm NH3 showed a response value of 5% at room temperature, whereas the other two samples exhibited much higher values towards similar condition NH3 at room temperature. Samples with nanowires showed a three-fold increase and samples with nanoparticles exhibit a two-fold increase in response value. We have found that the response of all samples increases with elevating the operating temperature up to 200°C. Increasing the operating temperature improved the nanoparticle sensing conditions more than the other two samples. The samples using nanoparticles showed a 33% increase in response towards 50 ppm NH3 at 200°C compared to the samples with thin films at similar conditions. Further, response and recovery time were investigated and reported in this study.

Pre-heating by defocusation of the CO2-Laser polishing beam: an experimental report from the lab-floor -INVITED

The laser beam polishing for glass and plastics is a purely thermal process and melts the ground or lapped structures to a depth of limited extent. This results in a smoothing of the surface, whereby the 1st - 4th order shape deviations can be corrected very well and transparent surfaces are created. The process is excellently suited for quartz glasses and other optical glasses with a low coefficient of expansion α. Furthermore, thermoplastics or metallic molds for injection molding and precision molding applications can also be polished with the laser beam. On the other hand, special measures are required for glasses with a high α, e.g. preheating of the component. For the investigations, a defocused laser beam was used for the defined preheating of glasses with high linear expansion coefficients. After reaching the material-specific preheating temperature, the laser beam was focused and the polishing process started. A defined cooling process follows again with a defocused beam. In this way, a ground biconvex lens made of boron crown glass was successfully polished. The laser-polished surfaces have an RMS value of 1- 3 nm. The polishing process can be used very flexibly. Likewise, very differently shaped optical components can be polished. The newly developed polishing regime is transferable to other optical glasses with high linear expansion coefficients.