Light for the Welding of Glass

Ultrashort laserpulses as a new tool for the bonding of glass

Photo: IAP

The processing of glass using mechanical methods such as cutting, lapping or polishing has been established worldwide. Nevertheless it is still a challenge to realize stable and reliable glass bonds. The often used glue or adhesive shows aging and outgassing. Alternative methods are usually based on thermal treatment processes, a fact which makes the joining of materials with different thermal expansion coefficients impossible.

Scientists explore how light can be used to realize stable and reliable bonds between transparent materials like glass. Extremely short laser pulses – so called ultrashort pulses – with a duration of merely 0.000000000001 s are essential for this work. Those pulses have to be focused to a tiny point with a diameter of less than a tenth of a human hair. This leads to such enormous intensities that atoms are torn apart and even transparent materials start to absorb. As a consequence the temperature of the glass is enhanced locally. If the time between the individual laser pulses is short enough the subsequent pulses can further increase the temperature and eventually lead to melting. The ultrashort laser pulses act in this case as a thermal point source. By placing the laser focus directly at the interface between two glass samples, they can be locally molten and welded.

Based on this idea, a process has been developed to realize stable and reliable glass bonds even between dissimilar glass. The achieved breaking strength of the laser welded glass very closely matches the one of the standard bulk glass sample. The field of application is very broad, ranging from the sealing of probes or endoscopes in medicine to the joining of lens systems or fiber components in optics, for example. Additional applications can be found in aerospace engineering, e.g. for the realization of ultra-light optical mirrors and lenses.

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