Ultrashort pulsed laser welding of bulk zinc selenide (ZnSe) to structural materials for optical applications.

Ultrashort pulsed laser welding of dissimilar materials has become an attractive alternative technique to commonly-used adhesive bonding for joining optics to metal mounts / assemblies in the manufacturing of optical and laser systems [1]. The laser welding process relies on very high peak intensities from a laser beam which is tightly focused through the top of a transmissive optical component, providing a focal spot in the vicinity of the optic-metal interface. Non-linear multi photon absorption in the optic and linear absorption in the metal results in a highly localised & contained plasma that rapidly cools to form a bond. For successful welding, the laser pulse repetition rate must be sufficiently high to provide thermal accumulation, resulting in a localised melt volume (the affected zone (HAZ)) surrounding the small plasma. The size of this HAZ is dependent on the laser processing parameters and material combinations used during the process and is typically on the ~100µm scale. As the laser spot translates across the material, this highly localised melt zone rapidly solidifies behind the beam and forms a strong bond (micro weld) between the two surfaces.
In this presentation, we present recent results on welding ZnSe, an important IR optical material. ZnSe is a semiconductor with a yellow tinge, with a wide transmission range from ~0.45µm to 21.5µm. It is commonly used as a window material for CO2 lasers emitting at 10.6µm. When doped with chromium (ZnSe:Cr) it can operate as an infrared laser at about 2.4µm. In our work polycrystalline ZnSe is welded to Aluminium alloy (Al6082) and Copper (C106). The influence of laser processing parameters such as pulse duration and repetition rate are presented alongside shear strength tests and accelerated lifetime tests on the ultrashort laser pulse welded components.