The pressure tool from the top must not only exert the necessary force on the weld seam, but also allow the laser to pass through.
Ideal is the pressing with a clamping glass, because it does not obstruct the laser beam nor the heat radiation for pyrometry.
However, if the upper part has protrusions, a flat glass plate can no longer be applied. A possible solution is a mechanically machined clamping glass.
As such a machined glass is relatively expensive and tricky because of possible breakouts of the glass edges. An alternative solution is to insert a machined acrylic glass as an intermediate plate between the upper part and the clamping glass.