Glass - Back to the Future!

Presenting Author:
Efstratios I. Kamitsos

article posted 6 April 2016

Efstratios Kamitsos has a degree in chemistry from the University of Athens, Greece. In 1983 he gained a PhD in physical-inorganic chemistry from Brown University, USA. In 1984 he joined the Theoretical and Physical Chemistry Institute (TPCI) of the National Hellenic Research Foundation in Athens, and is serving as the Director of TPCI since 1997. His research interests include structure and properties of glasses, and studies of the effects of electric fields, laser light and pressure on glasses. He was co-chairman of the Seventh ESG – 2004 (April 25–28, 2004, Athens, Greece).

Vibrational study of femtosecond laser-irradiated ULE glass

I. Efthimiopoulos1, S. Richter2,3, D. Möncke4, L. Wondraczek4, S. Nolte2,5 & E. I. Kamitsos1,*

Titania silicate glass with 7·5 wt% TiO2 is known as Ultra Low Expansion (ULE) glass, because of its very low thermal expansion coefficient near room temperature. This is a unique property for applications requiring geometrical stability like in substrates and mirror blanks. Recently, efficient nanograting formation in ULE glass was demonstrated by femtosecond laser processing which, in combination with light-induced darkening, make this glass ideal for future data storage applications [1]. Study of laser-induced structures in ULE glass by Raman, UV-Vis, and ESR spectroscopy showed the formation of hollow cavities containing molecular oxygen and surrounded by a compressed shell of glass, while photo-darkening was attributed to reduction of Ti4+ to Ti3+ [2]. The Ti3+ ions were suggested to form isolated tetrahedral and disordered octahedral sites with oxygen atoms. In this work we use infrared reflectance (Figure 1) and Raman spectroscopy (Figure 2) to investigate further the laser-processing effects in ULE glass. Key results include the reorganization of the silicate network in favour of four- and three-member silicate rings, a process leading to densification, and the arrangement of Ti3+–O sites into disordered Ti2O3-type clusters in the areas of glass exposed to the laser beam. Also, there is evidence for partial transformation of Ti2O3 clusters into polycrystalline Ti2O3.

Figure 1. IR reflectance spectra of pristine and laser-processed (grey and black) ULE glasses

Figure 2. Normalized Raman spectra of pristine and laser-processed ULE glasses

[1] S. Richter, C. Miese, S. Döring, F. Zimmermann, M.J. Withford, A. Tunnermann, and S. Nolte, Opt. Mater. Express 3, 1161 (2013).
[2] S. Richter, D. Möncke, F. Zimmermann, E.I. Kamitsos, L. Wondraczek, A. Tünnermann, and S. Nolte, Opt. Mater. Express 5, 1834 (2015).

The program DAAD-IKYDA 2015 is acknowledged for support.

1 Theoretical and Physical Chemistry Institute, NHRF, Athens, Greece
2 Institute of Applied Physics, Abbe School of Photonics, Friedrich-Schiller-Universität Jena, Germany
3 TRUMPE Lasertechnik GmbH, Ditzingen, Germany
4 Otto Schott Institute of Materials Research, Friedrich-Schiller-Universität Jena, Germany
5 Fraunhofer Institute for Applied Optics and Precision Engineering, Jena, Germany