Ultrafast welding joins glass to glass without adhesive or an interlayer
Focusing inside the interface between two transparent parts melts a small volume locally. The join is hermetic and the surrounding material stays cold.
Joining glass components has traditionally meant adhesive, optical contacting or frit bonding with a furnace cycle. Each has drawbacks: adhesives outgas and age, optical contacting demands extreme surface quality, and furnace processes heat the whole assembly.
Ultrafast laser welding provides a fourth option that is local, hermetic and adhesive-free.
How it works
The laser wavelength passes through the transparent material without absorption. Focused tightly at the interface between two parts in contact, intensity becomes high enough for non-linear absorption — multiphoton and avalanche ionisation — to deposit energy in a small volume.
That volume melts and, on cooling, forms a solid joint between the two parts. Scanning the focus traces a weld seam.
Because absorption only occurs where intensity is extreme, material outside the focal volume is unaffected. Components millimetres away stay at room temperature.
What the requirement is
Contact. The two surfaces must be in intimate optical contact at the weld location, because the process cannot bridge a gap. Surface flatness and clamping determine whether it works, and this is the dominant practical constraint.
Some approaches use burst-mode pulses to generate a larger melt volume that tolerates a small gap, which relaxes the requirement somewhat.
Where it is used
Microfluidic devices. Sealing channels in glass chips without adhesive that could contaminate samples or block channels.
Optical assemblies. Joining components where adhesive outgassing or index mismatch is unacceptable.
Hermetic packaging. Sealing sensors and MEMS devices where a true hermetic seal is required and the contents cannot survive a furnace.
Dissimilar joins. Glass to silicon, and glass to some metals, where thermal expansion mismatch would break a furnace-bonded joint.
The constraints
Joint strength is good but the weld is narrow, so seam layout determines assembly strength. Throughput is set by scanning speed over the seam. And the clamping fixture is often the hardest part of the engineering, since it must hold optical contact across the entire weld path without distorting the parts.
It remains a specialist process for applications where the alternatives genuinely do not work — which is a smaller set than the technique's flexibility might suggest, but a set where it has no competition.
This article was produced by the LasersNews AI desk and reviewed by our editors.
Related reading
Ultrafast lasers solved the quality problem. Throughput is the remaining one
Beam splitting, polygon scanning and higher repetition rates are the levers turning femtosecond precision int…
"Cold ablation" is a useful simplification that hides where the heat goes
Femtosecond pulses remove material before heat diffuses. Repeat them at high rates and heat accumulates anywa…
Filamentation cutting made thin glass a manufacturable material
Self-focusing inside the glass creates a column of modified material through the full thickness. The glass th…