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Femtosecond laser pulse nanostructuring of sodium silicate glasses

Name
Sergey
Surname
Fedotov
Scientific organization
Mendeleyev University of Chemical Technology of Russia
Academic degree
No degree
Position
Engineer
Scientific discipline
New materials, Manufacturing technologies & Processes
Topic
Femtosecond laser pulse nanostructuring of sodium silicate glasses
Abstract
Self-assembled birefringent periodical nanostructures known as nanogratings were induced by a femtosecond laser beam in R2O-SiO2 glasses with 5, 10 and 15 mol.% R2O (R=Na, K) and compared with those in fused silica. Obtained nanostructures possess similar period but number of laser pulses required to form nanograting grew substantially with alkaline oxide content that is presumably results from relatively slow migration of alkaline cations required to induce birefringence.
Keywords
nanograting, femtosecond laser, alkali silicate glass, birefringence
Summary

           

Femtosecond laser pulse nanostructuring of sodium silicate glasses

S.S. Fedotov, A.S. Lipatiev, S.V. Lotarev, V.N. Sigaev, P.G. Kazansky

 

Interaction between femtosecond laser pulses and oxide glasses provide different types of space-selective modification. Among them, self-assembled periodic nanostructures also known as nanogratings draw much attention due to their form birefringence similar to that of uniaxial negative crystals as they consist of periodic nanolayers with various density [1].Importantly, retardance and orientation of these birefringent structures depends on the pulse energy or number and orientation of polarization of the laser beam, respectively, and therefore can be controlled and predetermined optically. This feature together with the excellent thermal stability of nanogratings opens up the way to numerous applications requiring smart and durable patterning of microbirefringence inside the glass including polarization converters, holography and "everlasting" optical 5D-memory [2]. Several possible mechanisms of nanograting formation have been proposed [1,3,4] but this issue is still under debate.

            Most of studies performed were focused on obtaining nanogratings inside fused silica. Recently, evidence for femtosecond laser-induced nanogratings has been observed in glasses other than SiO2 including reports on nanogratings in GeO2 glass [5], binary titanium silica glass (ULE, Corning) [6], and several multicomponent borosilicate glasses (BK7, Borofloat, Schott) [6]. However influence of chemical composition of glass on nanogratings formation is still unknown.

            In the present work self-assembled nanostructures written by femtosecond laser beam (Light Conversion PHAROS SP regenerative amplifier, 1030 nm, 600 fs) are demonstrated in binary alkali-silicate glasses. Laser writing of nanogratings in R2O-SiO2 glasses with 5, 10 and 15 mol.% R2O (R=Na, K) is shown in comparison with fused silica. A period of nanostructures in alkalisilicate glasses is about 0.2-0.3 μm and is similar to a typical nanograting period in silica glass. On the contrary, a number of pulses giving rise to nanogratings grows with increasing alkali oxides content reaching ~105 pulses which is a few orders of magnitude higher than in pure fused silica. Still the final retardance corresponding to the prolonged laser treatment when process of nanograting formation is close to saturation approaches to that of the silica glass obtained by laser pulses with the same parameters. Local chemical analysis performed by means of energy-dispersive X-ray spectroscopy detected that alkaline cations partially move outside the area directly exposed to the focused femtosecond laser beam. Thus rise of birefringence presumably correlates to migration of alkaline ions and a long time required to form a nanograting as compared to that in fused silica may be related to the time which it takes to complete their migration.

            This study was financially supported by the ministry of Education and Science of the Russian Federation (grant 14.Z50.31.0009) and Russian Foundation for Basic Research (grant 16-03-00541).

References:

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