A process for joining optical materials by direct bonding reinforced by femtosecond laser welding is presented. It is
suitable for assembly of components for aerospace and high power laser applications where adhesives must be avoided.
Joining is realized in two steps. Firstly, materials are direct bonded so as to achieve a state of optical contact preferably
over the whole area between bonded surfaces. The second step consists in sealing the direct bonded region by writing
weld lines by femtosecond laser pulses at the outskirts of the bonding surface. The bond, applicable to both similar and
dissimilar material combinations, is resistant to important mechanical and thermal constraints and does not alter the
assembly’s optical transmission properties inside the sealed area. Most importantly, the drawbacks of common joining
methods are avoided, such as premature aging, degassing, photo-bleaching and limited applicable material combinations.
Previous work on welding of optical materials with ultrashort laser pulses demonstrated that the ability to
achieve good contact between components limits the applicability of the technology to only very small components. We
have overcome this limitation and demonstrated the capability to weld similar and dissimilar materials using
femtosecond laser pulses over several mm<sup>2</sup> areas between intimately contacted surfaces. Our joining process is realised
in two steps. Firstly, the two pieces which must be joined are direct bonded, thereby inducing optical contact throughout
the whole potentially bondable surface. Subsequently, the direct bond is reinforced by the inscription of femtosecond
laser weld seams in a sealing pattern in order to enclose the central region of the direct bond. We demonstrated the
applicability of this process to identical glass, dissimilar glass and glass-semiconductor. We also measured a mean
threefold increase in joint strength for such bonds between fused silica windows with only a few welding seams. The
final assembly is free from macroscopic surface deformations. Furthermore, by optimizing the laser exposure
parameters, we can avoid microscopic defects inside and around weld seams. Finally, the bonding method does not alter
the optical transmission properties at the center of the sealed region. As opposed to the use of adhesives, such bonds
resist to important thermal constraints and are free from chemical contaminants, degassing and ageing. Potential
applications may be considered in the fields of aerospace, laser manufacturing, semiconductor industry, solar cell
protection, precision manufacturing and many more.
We present a novel method for cutting thin borosilicate glass slides, as well as other results pertaining to laser
welding related to an existing technique. Based on the concept of stealth dicing for semiconductor wafers, we have
demonstrated that by giving our samples an initial stress and by creating optically induced defects inside the glass, it is
possible to efficiently cut a thin glass substrate. The edges are sharp along the whole length of the cut and exempt from
debris deposition and deformations. We have also perfected a femtosecond laser welding technique to join borosilicate
glass samples with very distinct welded regions.