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Femtosecond laser induced thermophoretic writing of waveguides in silicate glass  
Femtosecond laser induced thermophoretic writing of waveguides in silicate glass

Femtosecond laser


Ultrashort pulse lasers have proven to be unique and tremendously versatile tools for processing and modifying materials at a micrometer scale that surpasses conventional techniques.
Femtosecond lasers such as those used in the Institute of Optics applied to a material modify its structure, achieving modifications that are already being applied in fields such as 3D processing of materials with optical applications, micro / nano-surgery, nano-texturing. surface or the manufacture of micro-devices.

In this work, the thermophoretic redistribution of lattice modifiers in silicate glasses when worked with a femtosecond laser has been studied. When a femtosecond laser beam is focused into glass, a large amount of energy is absorbed, causing a local temperature rise of the order of 10,000 K.

thermophoresis


The thermophoretic distribution consists in that when the laser is applied, part of the glass melts, generating a temperature gradient around the point where the laser is applied that moves the particles out according to their weight and thus creating an organization in the structure of the material. which would be very expensive to obtain otherwise.

The mechanism of glass modification resembles the elemental thermal diffusion that occurs in the basaltic liquids of the Earth's mantle, but on a much shorter time scale (10 8 times faster) and over a well defined micrometric volume.
Since the optical properties of a glass, such as the index of refraction or the absorption of light, are highly dependent on its composition, controlling thermophoretic migration will allow the design of optically adjustable materials. This possibility has fostered research on the fundamentals of this phenomenon and its application in the field of photonics through local modifications of the composition of the treated material.

The silicate glasses used have been specifically designed to serve as wave guides in the infrared.
A common feature in femtosecond laser-induced static redistribution studies is the use of standard or commercial glasses.
Although these glasses are abundant and inexpensive, their composition makes it difficult to create high-performance photonic devices. For this reason, researchers have started a long-term research project to design and manufacture phosphate, borate, and now silicate glasses that can be written with a femtosecond laser.
A key feature is the modification of the glass composition by adding small amounts of heavy oxides, such as BaO, a naturally abundant and profitable material. The combination of these heavy oxides with other lighter modifiers (eg Na2O, K2O) allows them to produce positive local increases in refractive index after laser irradiation. Furthermore, scanning the sample perpendicular to the beam leads to the creation of continuous and smooth linear structures with high performance as infrared optical waveguides (the analogs to copper wires in electronics).

The work is a collaboration between the Institute of Optics, the Institute of ceramics and glass of the CSIC and the departments of physics of materials and of optics of the university Complutense of Madrid
 
Investigación financiada por el Ministerio de Ciencia e Innovación y la Agencia Estatal de Investigación
Instituto de Óptica "Daza de Valdés"
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