A new ceramic welding technology developed by engineers at the University of California, San Diego and the University of California, Riverside uses a series of short, ultrafast laser pulses to melt ceramic materials along the interface between two ceramic parts and fuse them together. Heat builds up only at the interface, so the melting is localized. The researchers call their method “ultrafast pulsed laser welding.” Laser-welded ceramic assembly consisting of a transparent cylindrical cap joined to a ceramic tube. Courtesy of Garay lab/UC San Diego Jacobs School of Engineering. To make this approach work, the researchers had to optimize the laser parameters (exposure time, number of laser pulses, and duration of pulses) and the transparency of the ceramic material. When these two aspects of the process are combined for optimal results, the laser energy couples strongly to the ceramic, allowing welds to be made using low laser power (less than 50 watts) at room temperature. Professor Guillermo Aguilar said that the “sweet spot” for the ultrafast pulses was two picoseconds, at the high repetition rate of one megahertz, along with a moderate total number of pulses. “This maximized the melt diameter, minimized material ablation, and timed cooling just right for the best weld possible,” he said. By focusing the energy of the laser precisely, the researchers were able to prevent temperature gradients from being set up throughout the ceramic, professor Javier E. Garay said. This allowed the researchers to encase temperature-sensitive materials without damaging them. Laser setup used to test and measure the transparency of ceramic materials. Courtesy of David Baillot/UC San Diego Jacobs School of Engineering. As a proof of concept, the researchers welded a transparent cylindrical cap to the inside of a ceramic tube. Tests showed that the welds were strong enough to hold vacuum. “The vacuum tests we used on our welds are the same tests that are used in industry to validate seals on electronic and optoelectronic devices,” said researcher Elias Penilla. The researchers said that until now there has been no way to encase or seal electronic components inside ceramics because the entire assembly would need to be put in a furnace, which would burn the electronics. Optical transmission through a transparent ceramic (left) versus a traditional opaque ceramic (right). Courtesy of David Baillot/UC San Diego Jacobs School of Engineering. The ultrafast pulsed laser welding process has so far been used only to weld small ceramic parts that are less than two centimeters in size. In the future, the team plans to optimize the method for larger scales, as well as for different types of materials and geometries. This new approach to laser welding could ultimately make ceramics integral components in devices for harsh environments as well as in optoelectronic or electronic packages that need visible-radio frequency transparency. The research was published in Science (https://doi.org/10.1126/science.aaw6699).