M.Sc. Malte Sander | RWTH Aachen University | Germany
Felix Schmidt | RWTH Aachen University | Germany
Prof. Christian Roos | RWTH Aachen University | Germany
In the material sciences glass ceramics are well known for their wide range of adjustable properties e.g. coefficient of thermal expansion, strength, optical properties. Usually, commercially used glass ceramics have isotropic properties due to the initially isotropic properties of the glass and the crystallization process which typically generates statistically oriented crystals. Nowadays, downstream processes, like the ion exchange process, exist to produce glass ceramics with anisotropic properties so-called functionalized glass ceramics. To reduce the production time as well as to widen the field of functionalized glass ceramics new methods have to be developed which are capable to induce anisotropic properties to the glass during the usual crystallization process.
In this study, the influence of electric fields on the crystallization of Li2O-Al2O3-SiO2 glass ceramics was examined to produce functionalized glass ceramics during the two-step crystallization process. Therefore, a plate capacitor with a voltage between 0.1 kV and 5 kV was installed in a crystallization furnace and samples with a diameter of 30 mm were crystallized. Possible effects from the electric field e.g. crystal orientations, differences in the degree of crystallization, crystal chemistry and structure were analyzed using XRD and SEM.
Creation and orientation by femtosecond laser irradiation of polar nanocrystals in silica-based glasses.
Prof. Bertrand Poumellec | UPSud - University of Paris Sud | France
PhD Jing CAO | Peking University | China
Dr.-Ing. François Brisset | UPSud - University of Paris Sud | France
Dr. rer. nat. Matthieu Lancry | UPSud - University of Paris Sud | France
We study the local crystallization produced by focused irradiation of femtosecond lasers in silica based glasses. We have pointed out that the following glass 33Li2O-33Nb2O5-34SiO2 exhibits the potentiality to precipitate LiNbO3 crystals that are optically non-linear active (e.g. second harmonic generation), when the laser pulse repetition rate is above 100-200kHz. We have shown that when the crystals are nanosized (low pulse energy), it is possible to orient them easily with the laser polarization.
During the presentation, I will make a short review on previous published results that used CW laser and the progress introduced by using femtosecond laser. I will suggest mechanisms showing the control of the crystallization and of the microstructure in the same time (phase separation distribution).
The important fundamental aspect here is that light polarization appears to be a new “button” that we can adjust in solid phase in order to control and orient a transformation, in short the immaterial acts on the material.
In the field of applications (integrated optics), the creation and control of the direction of the birefringence and of the second order optical properties open unprecedented possibilities.
For larger pulse energy, crystallites are larger (even if the scanning speed is low, it can be unique), but they are no more orientable. Nevertheless, the laser polarization continues to play an unexpected role on the microstructure.